Final Report for LS99-100
On-farm/ranch, rain fed alfalfa production was sustainable for at least four years on selected Coastal Plain soils. Estimated average annual hay yield ranged from 3.8 to 5.2 tons/acre. Net income at $135/ton of 12% moisture hay ranged from $130 to $302/acre/year with two intermediate income sites averaging $236. Continuous grazing of alfalfa in the Udic moisture region of the western Coastal Plain resulted in near complete stand loss in three years. Weight gains of beef cattle in an intensive put-and-take grazing system approximated weight gains of cattle continuously grazing common bermudagrass. Significant reduction of phytotoxic levels of subsoil aluminum using gypsum was not attained in three years. Biochemical analysis of alfalfa samples from these gypsum-treated sites indicated that gypsum and low rates of boron were beneficial for alfalfa growth. Alfalfa protein, hexose, and chlorophyll contents responded inconsistently to the amendment treatments.
Develop a soil amendment and nutrient management plan to enhance establishment and sustainability of alfalfa on acid, Coastal Plain soils.
Develop multi-option defoliation strategies using hay, silage, green chop, and/or grazing to improve stand survival and sustainability of alfalfa.
Develop risk assessment models to project economic benefits from alfalfa production on Coastal Plain soils.
Use a variety of the latest technologies to transfer best management practices to stakeholders in the southern US.
Stakeholders on Coastal Plain soils in the southern U.S. have not had sustained success in maintaining a dependable, high nutritive value, perennial forage legume for livestock production. Alfalfa serves this purpose in northern, Midwestern, and western states, but it has not become a reliable forage crop on Coastal Plain soils due to its intolerance to excessively wet and poorly aerated soils, inadequate soil fertility, root-growth sensitivity to soil acidity, and to the humid conditions that restrict efficient hay curing. Studies were needed to fine-tune site selection and soil management for reliable establishment and sustainable production of alfalfa, and to evaluate alternative mechanical harvesting and livestock grazing schemes in the southern region of the US to develop production risk management guidelines.
Cash receipts from beef, dairy, horse, and hay production, estimated recently at $636 million in eastern Texas, account for 42% of the state’s income from basic agricultural production. Nearly 2.7 million head of beef cattle thrive on 6.5 million acres of forage. Of Texas’ 373,000 dairy cows, 40% are located on Coastal Plain soils. Currently, perennial grass pastures are the foundation for these livestock industries throughout the southern US Coastal Plain. Because of its nutritive value, alfalfa is excellent forage for livestock production. Alfalfa hay fed to dairy animals in Texas is valued at $45 million annually, and that fed to beef cattle and horses increases this value to about $70 million. However, only a small fraction of this alfalfa is produced in Texas, with most being imported from states to the north and west of Texas. A similar situation exists in Arkansas and across the South.
Precipitation averages more than 45 inches across the Coastal Plain. Ultisols, the primary soil order on the Coastal Plain, are highly leached, acid, and have a sandy texture in the A-horizon. ‘Coastal’ bermudagrass, a warm-season perennial, has been the primary improved forage of choice in this region for more than 40 years. To achieve the genetic potential for quality hay, Coastal bermudagrass requires approximately 100 lb of N/acre for each of four or more cuttings, and for grazing, about 60 lb of N/acre usually are applied to bermudagrass pastures three or more times during the grazing season. High N rates rapidly acidify low-buffer-capacity soils and elevate the need for limestone when an ammonium source of N is used. Legumes metabolize atmospheric N fixed by rhizobia in a symbiotic relationship with plant roots. Alfalfa production on Coastal Plain farms and ranches would provide a warm-season perennial forage with greatly improved nutrient content and feeding value for livestock without the use of fertilizer N and, as an additional benefit, would decrease the rate of soil acidification.
Aluminum solubilizes from soil minerals at pH levels below 5.5 and solubilization exponentially increases as pH declines below 5.0. In strongly acid soils, Al toxicity inhibits root growth in sensitive plants, thereby limiting uptake of water and nutrients. Acidity in surface soils can be neutralized by incorporation of limestone. However, neutralization of subsoil acidity using limestone is a long-term process. Successful reduction of toxic levels of Al in subsoils would allow producers to grow alfalfa on a wider range of soils throughout the Coastal Plain.
Rainfall across the Coastal Plain is generally adequate and timely for production of five or more tons of alfalfa/acre. Economic estimates based on our small-plot experiments indicated that farmers could net from $200/acre the seedling year to about $325/acre in succeeding years by producing alfalfa for hay (Clary and Haby, 1998a). The cost of lime to raise soil pH to 7.0 is offset by the savings from curtailed use of N fertilizer since Rhizobia on alfalfa roots fix atmospheric N for plant use. Under simulated haying conditions, we maintained alfalfa stand density for six years in research plots before significant stand reduction occurred. Diseases were minimal and cotton root rot is not prevalent on acid sandy soils.
Commercial alfalfa production on Coastal Plain soils can be a reality. Alfalfa has the potential to generate more income without supplemental irrigation than most field crops grown in the southern and southeastern US. Various harvesting methodologies such as wrapping high-moisture hay bales in plastic, green chopping, ensiling in plastic bags or bunkers, and grazing are potential alternative harvesting strategies for producers in the Coastal Plain region. The environmental and economic benefits of alfalfa production are positive. Curtailing N fertilization on Coastal Plain soils slows the increase in soil acidity that occurs in grass production systems that require high rates of N to produce high nutritive value forage. Decreased nitrification lowers the potential for nitrate leaching into ground and surface waters. Plant nutrient uptake and use efficiency of fertilizers is improved at soil pH levels near neutrality. Improved milk production and weight gains have been demonstrated for livestock fed alfalfa hay compared to bermudagrass hay.
Some questions concerning alfalfa production systems on Coastal Plain soils remain unanswered. We have shown that subsoil Al at phytotoxic levels decreases yield of alfalfa (Beedy, 2000). Production declines more rapidly when phytotoxic levels of Al are nearer to the soil surface compared to when they are at deeper depths, particularly during drought conditions. Selection of the appropriate harvest technique according to expected and prevailing climatic conditions and livestock grazing management on alfalfa need refinement in the Coastal Plain region. Finding a solution to these problems would enhance the production of alfalfa as part of a holistic approach to forage management on livestock farms in the South and southeastern US.
Livestock and forage grower-stakeholders are interested in growing alfalfa on their farms after historically being told that alfalfa could not be grown on Coastal Plain soils. The five stakeholders were chosen based on their commitment to forage agriculture, their willingness to collaborate in the development of a “new industry” for the southern region, and their dedication to adhering to research guidelines and protocols. They were all keenly aware of the need to develop alternative, locally grown high nutritive value roughage for livestock.
The development of grazing-tolerant, dual-purpose varieties of alfalfa, such as Alfagraze in Georgia (Bouton et al., 1991), has increased the potential for successful and economical (Clary and Haby, 1998b) production of alfalfa on the US Coastal Plain where humid conditions make curing difficult for this crop. Soils of the Coastal Plain predominantly are Ultisols (Buol et al., 1973). Ultisols are acid, sandy soils that have a low buffer capacity and need limestone to reduce surface soil acidity for growth of acid-sensitive crops such as alfalfa. Phytotoxic levels of Al in subsoil horizons also can hinder alfalfa production (Beedy et al., 1995). Neutralization of toxic levels of Al in subsoil will allow alfalfa to grow on a wider range of soils throughout the Coastal Plain. There are conflicting reports on the efficacy of surface-applied limestone in neutralizing subsoil acidity (Sumner, 1995). Movement of the alkalinity to the subsoil from surface-incorporated limestone is slow. Plant-available soil boron becomes unavailable when low organic matter, acid sandy soils are limed to pH 7.0 (Haby et al., 1995). Under these conditions, B rates up to 3.75 lb/acre were economical for production of alfalfa (Haby et al, 1998).
Gypsum (CaSO4∙2H2O), a neutral salt, detoxifies subsoil Al (Pavin et al., 1984; Oats and Caldwell, 1985; and Sumner et al., 1986). Yield responses were obtained in Brazil, South Africa, and the southeastern US to applications of both mined and by-product gypsum applied at rates of 0.5 to 4.5 tons per acre (Sumner, 1993). When gypsum, which is slowly soluble (Budavari et al., 1989), is applied to the surface horizon of a soil that has acid subsoil, solubilized calcium (Ca) and sulfate (SO42-) are moved into the subsoil through a series of adsorption, fixation, and exchanges aided by gravitational water flow. The leaching of these ions supplies Ca and S, increases soil ionic strength, reduces the percentage Al saturation of the exchange complex, and, in gypsum-responsive soils, slightly raises subsoil pH (Sumner, 1995) allowing roots of acid-sensitive plants to proliferate and extract water and plant nutrients in previously unavailable zones.
Gypsum is also a co-product of electricity production at coal and lignite fired generators. Flue gas is scrubbed through lime slurry to remove sulfur dioxide (SO2) and form calcium sulfite (CaSO3‾). Calcium sulfite is purged with air using a catalyst to oxidize the sulfite to sulfate (Pasluk-Bronlkowska et al., 1992). At some generating plants the purging step is omitted, leaving co-product CaSO3‾ that is disposed as a waste product. Calcium sulfite, which is slightly soluble in water, is thermodynamically unstable in air and slowly oxidizes to CaSO4 (Windholz, 1976). Ritchey et al. (1995) evaluated the effects of CaSO3‾ on plant growth in laboratory conditions and stated that additional testing was needed to determine crop response under field conditions.
In the South, alfalfa yields in research trials were comparable to hybrid bermudagrass fertilized with 178 lb of N/acre, but the alfalfa crop contained almost twice as much crude protein (Brown and Byrd, 1990). Alfagraze alfalfa persisted for three years under continuous grazing for 120-day periods on Piedmont soils in Georgia (C. S. Hoveland, Personal Commun.). Over the past eight years, we have evaluated soil series, soil fertility, and other production requirements for alfalfa, and successfully grew ‘Alfagraze’ under simulated haying conditions on ten Coastal Plain soils (Haby et al., 1997). Alfagraze direct-drilled into a Coastal bermudagrass pasture persisted only two seasons under rotational grazing on an upland, sandy Coastal Plain soil (Rouquette and Haby, 1996). To maintain highest yields of crude protein, grazing cycles on bermudagrass have been set at 21 to 28 days (Aiken et al., 1991); whereas, alfalfa needs longer than a 30-day interval between grazing cycles to allow recovery (Van Keuren and Matches, 1988).
Bermudagrass is the standard summer pasture for cattle in much of the southern US, but yields, forage quality, and animal performance have been poor during the hot, dry, midsummer weather (Utley at al., 1974). Stocker cattle average daily gain (ADG) during that period generally is low (Utley at al., 1974; Greene et al., 1990). New alfalfa varieties with improved grazing tolerance (Counce et al., 1984; Smith et al., 1989) have increased interest in alfalfa as a pasture forage. Alfalfa has produced ADG of 0.79 to 1.94 lb/ day over the grazing season and annual calf gains of 217 to 496 lb/acre in the Coastal plain region (Hoveland et al., 1988; Bates at al., 1996).
However, persistence of alfalfa stands in the Coastal Plain region tends to be poor under limitations of pests, low soil pH and fertility, and inadequate drainage (Haby et al., 1997). Fertility and pH limitations of Coastal Plain soils are manageable and alfalfa can be grown on soils with water tables as close as 1.5 ft below the soil surface (Haby et al., 1997). Because alfalfa is deep-rooted, we hypothesized that it would be more drought-tolerant than bermudagrass during summer dry periods, and possibly able to sustain higher cattle gains. Therefore, we compared performance of stocker calves grazing each type of pasture in summer for two years on a Coastal Plain soil. Objectives were to determine if alfalfa could persist under grazing conditions in the hot, humid southeast and to determine animal performance when compared to the performance of cattle grazing bermudagrass pastures.
Alfalfa regrowth potential after serial harvests, and persistence after livestock grazing have been studied extensively (Volenec et al. 1996; Tesar and Yager 1985), but the biochemical determinants of sustainability (Dhont et al. 2002) on amended soils have not been investigated. Studies are needed on the responses of alfalfa metabolism to holistic best management practices that embody the neutralization of soil acidity and Al toxicity, nutrient management, and multiple-option serial harvesting strategies so that risk assessment models can be developed that may be applied to specific farm situations to quantify the biological efficiencies and sustainability of alfalfa production on the Coastal Plain soils.
However, the response of plants to Al is monitored in the root exudates (Ma et al. 1997; Osawa et al. 1997) there being no direct plant enzyme assay for assessing Al toxicity. Similarly, the response of plant metabolism to B deficiency is usually monitored as B-complexing polyols in phloem exudates (Hu et al. 1997). There are only a few studies on the responses of photosynthesis, and protein contents to the combination of gypsum, limestone and/or B amendments of soil (Dixit et al. 2002, Mahboobi and Yucel 2000, Brown and Hu 1997); the lack of interest being due in part to the complexity of the metabolic antagonism between Al toxicity and B deficiency (Yau 2000, Camacho-Cristobal and Gonzalez-Fontes 1999, Yang and Zhang 1998). This is because Al in acid soil inhibits Ca uptake by blocking Ca channels in the plasma membrane (Huang et al. 1992, Horst et al. 1999) thereby causing Al-induced Ca deficiency. Boron deficiency, like Al toxicity causes cessation of root growth (Heyes et al. 1991, Bohnsack and Albert 1977). On the other hand, Al3+ retards senescence and stabilizes plant protein and chlorophyll contents (Subhan and Murthy 2000). The antagonistic responses of plant metabolism to Al, B, and Ca could render the biochemical results of such projects of little or no practical utility for the management of soil acidity for sustainable crop production. In order to avoid possible contradictory experimental data, we analyzed the alfalfa glutamate dehydrogenase (GDH) activities since the enzyme isomerizes by discriminating and integrating metabolic signals and in that way synthesizes some RNA (Osuji et al. 2003), regulates not only biomass (Osuji et al. 2003/4; Ameziane et al. 2000; Osuji and Braithwaite 1999) but also tissue differentiation (Osuji and Madu 1997). In addition, in order to explain possible contradictory experimental data, fructose 1,6-bisphosphatase (FBPase) activities were analyzed. FBPase is the Calvin cycle enzyme that hydrolyzes fructose-1,6-bisphosphate to fructose-6-phosphate in the regeneration of ribulose-5-phosphate from triose-phosphate (Leegood 1990). The enzyme is important in the study of sustainable forage production on amended soils because of its role in the fixation of CO2 and its activation by Ca2+ (Kreimer et al. 1988). Because B forms complexes with ribose, it interferes with nucleotide, NADH, and nucleic acid metabolism (Johnson and Smith 1976). Nucleoside triphosphates are the substrates of GHD besides being the strongest inducers of the enzyme=s isomerization (Osuji et al. 2003/4). Therefore, the effect of B on nucleotide metabolism might illuminate the antagonistic response of carbohydrate metabolism to B and Ca amendments of soil. ATP that is a major product of photosynthesis is known to regulate the Calvin cycle. In this paper, we report that amendments of soil with combinations of gypsum, boron, and limestone decreased the FBPase activity, the nucleoside monophosphate concentration, and the RNA synthetic activity of GDH with or without changes in the protein, chlorophyll, and hexose contents. The electrophoretic profiles of the RNAs synthesized by GDH were representative of the sum total effects of the soil amendments and serial harvesting on the sustainability of alfalfa production on the Coastal Plain soils.
Objective 1. Field Study. Two Coastal Plain soils were selected that have good drainage and phytotoxic levels of subsoil Al determined by increment sampling to 48 inches and analyzing for 0.01 M CaCl2 pH and Al (Hoyt and Nyborg, 1972). These sites were located on university lands near Overton and Nacogdoches. Limestone to raise pH to 7.0 was incorporated by disking 6-inches deep in early spring. Gypsum at rates of 0, 2.27, 4.54, and 6.81 tons/acre and calcium sulfite at rates equivalent to the Ca in gypsum were applied to 200 ft2 plots in four replications in a randomize complete block design and incorporated with the limestone.
All plots were sampled at depths of 0 to 6, 6 to 12, 12 to 24, 24 to 36, and 36 to 48 inches before treatment and semi-annually to monitor treatment effects. Samples were analyzed for sulfur and Mehlich-III extractable P, plant nutrient cations and any heavy metals determined by analysis (Soltanpour et al., 1996) to be in excess in the calcium sulfite. Soil pH was determined in a 2:1 suspension of soil to water and in 0.01 N CaCl2. Aluminum extractable in 1.0 M KCl and exchangeable in 0.01 M CaCl2 was determined.
Before seeding in fall, each site was fertilized based on soil analysis for alfalfa production. A grazing-tolerant variety of alfalfa (dormancy rating of 4) was planted at 20 lb of treated, inoculated seed/acre on each field site the fall following soil amendments and treatments. Yield data were collected at approximately 30- to 35-day intervals for two seasons using a Hege 211-B forage harvester. Oven-dried plant samples were analyzed for P, K, Mg, Ca, Mn, Na, Fe, Cu, and Zn using ICP. Plant biochemical responses to treatment including chlorophyll (Isaac, 1990), fructose 1, 6-bisphosphatase (Leegood, 1990), stored carbohydrate (Isaac, 1990), glutamate dehydrogenase activity (GDH) (Loyola-Bargas and Jimenez, 1984; Osuji and Madu, 1995; and Garland and Dennis, 1997) and GDH amination activity (Osuji and Madu, 1997) were determined on freeze-dried samples.
Glasshouse study. A soil containing phytotoxic levels of exchangeable Al was excavated homogenized by depth, and placed into 4-inch-diameter by 50-inch-deep PVC pots in the same order that depths occurred in the field. A PVC cap was sealed to the bottom of the pot and fitted with a tube to transfer leachate to collection bottles. The surface 6-inch depth of soil was treated with ECCE 100 limestone to raise pH to 7.0 and fertilized for alfalfa. Four replications of gypsum treatments equivalent to 0, 2.25, and 4.5 tons per acre were applied and mixed into the surface 1-inch depth. One calcium sulfite treatment was applied at a rate of Ca comparable to the Ca level in the high rate of gypsum. Deionized water was applied to leach the gypsum into the subsoil. Leachate was analyzed for Ca, Al, and S. Inoculated alfalfa seed was planted when evidence of gypsum occurred in leachate. Seedlings were thinned to five per pot. Adequate deionized water was applied to the alfalfa to continue the gypsum leaching process. Five harvests of alfalfa were made under optimum moisture conditions. A moderate drought stress was imposed during additional growth periods to evaluate the effect of gypsum on alfalfa rooting depth. At the end of this experiment, the PVC pots were sectioned by depth for root mass and length determinations. Soil at each depth was analyzed for pH and exchangeable Al, Ca, Mg, SO4-S, and K. Alfalfa yield estimates, root mass and length, alfalfa nutrient content, photosynthetic rate estimates, carbohydrate content, and glutamate dehydrogenase enzyme activity, and soil nutrient content were analyzed to determine the success of treatments for reducing Al toxicity. Data resulting from these studies were evaluated using SAS (1994) to determine the effectiveness of treatments on alfalfa yield, nutrient content, rooting depth, plant biochemical responses, nutrient leaching, and reduction in Al toxicity. Plant growth, nutrient content, and biochemical responses were related to soil responses to amendment treatments.
Objective 2. This phase of the project was three dimensional and incorporated farmer (stakeholder) alfalfa establishment, production evaluation, and economic assessment; research assessment of alfalfa variety stand maintenance to grazing pressures; and a grazing experiment to document animal performance on grazed alfalfa compared to grazing bermudagrass.
Stakeholders. Five stakeholders whose farms represent an array of soil types, size of operation, and management expertise were involved with scientists to demonstrate proper selection of sites for adequate drainage, aeration, and favorable acidity levels, and to learn site preparation and alfalfa production from soil amendment to establishment through production and marketing. Sites on stakeholder’s farms were sampled to 48 inches by one-foot depths for analysis of pH. Sites with subsoil pH above 5.5 and with good drainage were selected for alfalfa establishment. The level of exchangeable aluminum (Al) was determined in subsoils with pH <5.5. If 0.01 M CaCl2 Al levels in the subsoil depths were greater than 1.5 ppm, an alternate site was selected, or gypsum applied to reduce the phytotoxic effect of the Al. Chosen sites were sampled to the 6-inch depth and the samples were analyzed for pH and lime requirement. Limestone was applied to raise soil pH to 7 and incorporated by disking the top 6 inches of soil in late winter-early spring. Limed sites were resampled in late summer and analyzed for fertility level and pH change in the 6-inch depth. If needed, additional limestone was applied. A blended fertilizer containing recommended rates of P, K, Mg, S, and B was applied before seeding alfalfa. Preplan fertilization included 120 lb P2O5, 150 lb K2O, 40 lb S, 20 lb Mg, and 4 lb B. After light disking, fields were planted at 25 lb of treated seed per acre when sufficient rainfall occurred in late November to establish the alfalfa. Potash was reapplied at the rate of 100 lb K2O per acre after the second cutting. Additional potash was reapplied after the fourth cutting at the rate of 100 lb K2O with additional sulfur and magnesium at rates of 40 and 20 lb per acre, respectively. Half of each field was seeded to Amerigraze 702 and half was seeded to GrazeKing. Insect and weed infestations were monitored and appropriate controls applied as needed. Alfalfa weevil was an annual problem. Weevil control was accomplished by spraying with Sevin XLR Plus or Fury. Occasional infestations of alfalfa leafhopper were controlled using these same insecticides or Malathion. Aphids annually attacked the alfalfa, but these were biologically controlled by lady beetle populations that occurred naturally. Grass weeds including ryegrass were controlled using Poast. Common bermudagrass that gradually increased in the alfalfa was difficult to control. Broadleaf weeds were controlled using Pursuit. Pigweed and dock were difficult to control. A meter-square quadrat was used to sample regrowth of alfalfa within each variety in of each stakeholder’s alfalfa field using a 4-blocked component. Sustainability of alfalfa stand was quantified by stand density ratings at the end of four production years. Varieties X Grazing Pressure. Six alfalfa varieties with varying dormancy ratings ranging from 2 to 7 and reported to have tolerance to grazing were planted at the Texas A&M University Agricultural Research and Extension Center at Overton in the autumn of 1997. ‘Alfagraze’, ‘Amerigraze 401+Z’, ‘Amerigraze 702’, ‘Cimarron 3I’, ‘GrazeKing’, and ‘HayGrazer’ were drilled (7-inch centers) in 21-foot wide x 150 foot long grazable plots. Each variety was randomly included three times in each of two 1.5 acre blocks; thus, each variety was represented six times (reps). Each of the 1.5 acre blocks was sub-divided longitudinally into three strips for stocking treatments that were 50-foot wide x 450’ long. Each 50-foot wide strip was randomly assigned to the following stocking treatments: Continuous stocking with yearling, 650-lb calves during the summer months and regulated so that stubble height was about 3 inches. Although this management scenario allowed for removal of animals for short durations, it was not rotational stocking; Rotational stocking in which grazing was initiated when most varieties were at Stage 3 (prebud) and stocking continued until an approximate 3-inch stubble height was prevalent; Rotational stocking in which grazing was initiated when most varieties were at Stage 5 (10% bloom) and stocking continued until an approximate 3-inch stubble was prevalent. The duration of stocking on all rotational treatments was usually less than three days. Thus, the primary stocking objective was to mimic “rapid” grazing systems that may be implemented in a commercial dairy or beef operation. The two 1.5 acre blocks planted to alfalfa were treated with Roundup during the summer of 1997 to eradicate bermudagrass. Both areas were disked several times and 3 tons/ac ECCE-100 limestone were incorporated via disking to buffer soil pH from 5.2 to approximately 7.0. The area was roller-packed during late summer and varieties were seeded on November 4, 1997. Pre-plant fertilizer of 0-100-100-50-25-1 lbs/ac, respectively, N-P2O5-K2O-S-Mg-B was applied. Thereafter, alfalfa was fertilized at this rate during late winter-early spring of each year. During 1998, alfalfa was not grazed but rather was harvested as hay on April 29, 1998. In 1999, all alfalfa was harvested as hay on March 23 and again on May 25. For each hay harvest, sub-samples for DM yield were taken from each variety using a Hege 211B self-propelled Forage Harvester. After these hay harvests, all plots were grazed at one of three stocking methods through beginning 6-19-99 and terminating after the 2001 grazing season. One June 16, 1999, each plot (n=108) was identified with a permanent marker at two locations/plot for pre- and post-experiment measurement of alfalfa stand sustainability. At the June 16 initial measurement date, two measurements per plot were made at two separate locations and by different individuals (sets) to assess plant height, number of plants, and number of stems inside a 21” x 24” quadrat (3.5 ft2) Plants were counted in-place (non-destructive) and stems were counted by clipping plants to a 3-inch stubble inside the quadrat. On November 5, 2001, the exact location for each variety x stocking method plot was relocated and again measured for height, number of plants, and number of stems at two locations and by separate individuals. In addition, the entire plot area (21’ x 50’) was visually scored by two people for percent stand using canopy cover as the assessment criteria. Sustainability attributable to variety and stocking method were based on differences between the initial and final measurements in addition to the final assessment of visual percent stand. During the grazing season for each year, each plot (variety x stocking method) was measured for stand height at initiation and at termination of stocking. In addition, for rotational stocked plots, stage of growth was recorded at initiation of each grazing cycle. Nutritive value assessments for neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein were taken from each variety x stocking method treatment at approximate 2-week intervals throughout the initial (1999) and final (2001) year of evaluations. Animal Performance. A grazing trial comparing alfalfa to bermudagrass was initiated at the Southwest Research and Extension Center at Hope, Arkansas to quantify livestock performance. Four replicate pastures of each forage were assigned in a completely randomized design. An alfalfa variety having a low to medium dormancy rating and having proven grazing tolerance, was fall seeded (1999) on a clean-tilled site. The trial was conducted on an Ora fine sandy loam (fine-loamy, siliceous, thermic Typic Fragiudults) at the Southwest Research and Extension Center, University of Arkansas, Hope, AR. All pastures were two acres in size and were in common bermudagrass managed for grazing prior to division into treatments. Pastures were assigned to forage treatments based upon drainage characteristics and initial subsoil pH and aluminum concentrations following soil profile testing to a depth of four feet. Four pastures remained in common bermudagrass (average initial pH and Al to the two-foot depth, 5.4 and 2.0 ppm, respectively) and four were renovated in 1999 to pure stands of alfalfa (average initial pH and Al to the two-foot depth were 5.7 and 0.7 ppm, respectively). Renovation to alfalfa was accomplished after killing existing bermudagrass sod with glyphosate. Soil amendments (lime, gypsum, K, P, S, Mg, and B) were applied according to recommendations of Haby et al. (1997) for Coastal Plain soil. Limestone was applied to correct topsoil pH and gypsum was used to ameliorate possible aluminum toxicity in the subsoil (Sumner, 1995). Pastures were disked to a 15-cm depth four times between June 15 and Sept. 15 to incorporate soil amendments and break up the sod. After the final disking, soil was smoothed, cultipacked, and left as a fallow seedbed for one month prior to planting. Alfalfa (‘Graze King’, grazing–tolerant, fall dormancy rating 4 to 5) was inoculated with Rhizobium meliloti and drilled into the undisturbed seedbed at a depth of 0.25 in and a row spacing of 6.0 in on October 21, 1999. Seedling-year alfalfa pastures were hayed twice prior to grazing in spring 2000 (April 18 and May 23) in order to give seedlings maximum time for root development. Alfalfa stand density was measured in March of each year and in October 2001 by counting crowns and stems in six randomly selected 1-ft2 quadrats per pasture. Pastures were located on a well-drained, sandy loam site suitable for alfalfa. Alfalfa and bermudagrass were managed to optimize forage production throughout the experiment using best management soil treatments developed by scientists at the Texas Agricultural Experiment Station at Overton. Proposed alfalfa pastures were limed to pH 7.0 in late winter-early spring 1999. Lime was incorporated by disking into the top six inches of soil. Existing common bermudagrass swards were eradicated with Round-Up (glyphosate, 5 qt/acre) in spring 1999, and an annual warm-season grass was planted for a hay crop. In October 1999, alfalfa was no-till drilled (20 lb PLS/acre at 10-inch row spacing). Appropriate herbicides were applied to control annual grasses and broadleaf weeds during establishment. The first growth of alfalfa in spring 2000 was harvested as hay prior to the initiation of grazing. Zorial (norflurazon, 1.25 lb/acre) was applied to control emerging weeds in established alfalfa stands during the non-grazing season. Insects, primarily the alfalfa weevil in late winter, were controlled as needed. Pastures were rotationally grazed beginning in 2000. Each 2-acre pasture was subdivided into six 0.33-acre paddocks. Each pasture was initially stocked with two calves per acre. Bermudagrass was rotationally grazed at approximate 21 to 28-day rest cycles to maintain highest yields of crude protein (Aiken et al., 1991). Alfalfa was rotationally grazed on a schedule to accommodate a 30 to 60-day recovery period between grazings (Van Keuren and Matches, 1988). Graze-rest cycles were adjusted based on stubble height and forage mass as forage growth varies with climatic conditions. Stocking rates were adjusted using the put-and-take method as needed to control forage utilization (mass). Forage mass was measured using a rising plate meter and clipping. Forage samples were collected once a month from a pre-graze and a post-graze paddock from each pasture for analysis of crude protein, neutral and acid detergent fiber, and in vitro dry matter digestibility. Alfalfa stand counts (stems per square foot) were obtained prior to the start of grazing each year. Alfalfa stands were scored each month for evidence of disease. Uniform sets of preconditioned (weaned, immunized, castrated, wormed, dehorned) English/ Brahman cross (less than 25% Brahman) calves (approximately 450 lb initial weight) grazed from May to late September as adequate forage was available. Two pounds per day per head of a supplement containing corn, minerals, and Rumensin were fed to all calves. Poloxalene was added to the supplement for calves on alfalfa pastures to control bloat. Extra calves for put-and-take stocking were grazed on bermudagrass pastures and fed the same supplement as calves in treatment pastures until needed. Weather data (maximum and minimum air and soil temperature, precipitation) were recorded at the site daily. Soil samples were collected from each pasture paddock prior to planting of the treatment forages and again at the conclusion of the trial. Soil samples were analyzed for organic matter, NO3, K, P, Mg, S, and pH to evaluate changes in soil nutrient concentrations under the different forages. Records of all production-related costs (equipment, fertilizer, pesticides, feed, and labor) incurred on the two forage systems were kept for comparison with income (value of beef weight gain). Objective 3. Economic Projections. Economic decision models and operational budgets were modified based on actual on-farm inputs and returns generated from field-scale, on-farm alfalfa production. These economic models will serve as guidelines to establish a new hay industry for communities and clientele in the southeastern U.S. The current stored forage demands are being met with either grass hay or silage and/or imported alfalfa from northern, western, and Midwestern states. Objective 4. During the course of this study, multi-county field days and tours were conducted to view, examine, and discuss holistic, sustainable management practices for alfalfa on acid soils. These events were held at state Research and Extension Centers as well as on individual stakeholder properties. Research and Extension personnel and stakeholders shared their experiences and management expertise with local producers and on-farm production was encouraged. Publications, video materials, Internet, radio agricultural programs, and related communication methods were used to educate scientists and stakeholders on successful management principles, utilization strategies, and risks associated with alfalfa production. Technologies used and developed in this study should be applicable across the Coastal Plain of the southern US and will be valuable components of related discipline research endeavors.
Reduction of subsoil aluminum for alfalfa production.
Strongly acid soils solubilize aluminum (Al), thereby limiting the growth of Al-sensitive crops such as alfalfa (Medicago sativa L.). Management of acid subsoils can be difficult due to physical and economic constraints. Field experiments were conducted on Coastal Plain soils at two locations in east Texas to evaluate the effectiveness of surface-applied gypsum and a flue gas desulfurization by-product for reducing the toxic effects of acid subsoils on alfalfa. A Cuthbert fine sandy loam (clayey, mixed thermic Typic Hapludult) in Rusk County and a Sacul fine sandy loam (clayey, mixed, thermic Aquic Hapludult) in Nacogdoches County were selected because pH was low and soluble Al high in the subsoils. The materials were applied at rates of 0, 5, 10, and 15 Mg ha-1. In addition, a glasshouse experiment was conducted that used 0, 2.25, and 4.5 tons of gypsum per acre. Field soils were sampled to 48 inches prior to treatment. Samples were separated by depth at zero to 6, 6 to 12, 12 to 24, 24 to 36, and 36 to 48 inches. Soils at both sites were sampled four additional times during the study. However, the sampling two months after treatment was only to 24 inches at both sites. The Mehlich-3 extraction procedure was used to remove exchangeable bases in addition to P, S, Al, Fe, Mn, Cu, and Zn. Extractable Al was determined using normal KCl. Aluminum and manganese exchangeable in 0.01 M CaCl2 were also determined. Filtrates of all extractions were analyzed using ICAP. In addition, pH in a 1:2 soil to water suspension, and 1:2 soil to 0.01 M CaCl2 was measured on all samples. Electrical conductivity was measured beginning with the samples collected in the year 2000 at both sites. Field studies were concluded 41 and 45 months after treatment at the two locations. No significant effect of material on alfalfa yield or tissue mineral concentration was observed. In addition, amendment application rate did not affect yield. However, there were rate-related differences in nutrient concentrations in plant tissue in several harvests. Analysis for Ca and S indicated these elements moved into the soil profile to depths of 24 and 48 inches, respectively, by the conclusion of the study. Subsoil pHH2O and pHCaCl2 were not affected by treatment. Movement of Ca and S into the soil did not reduce M KCl extractable and 0.01 M CaCl2 exchangeable Al. In the glasshouse study, alfalfa yields and root growth were not affected by gypsum rate. As gypsum rate increased, plant tissue S increased, but K and Mg decreased. Alfalfa roots did not grow below 24 inches, even though there was evidence of material movement to 36 inches in the soil. Although sulfur moved to 30 inches, no effect on soil Al was observed. Leachate collected from the bottoms of columns indicated that soil cations were leached as a result of gypsum application. The applied rates of gypsum and a flue gas desulfurization by-product did not significantly affect the acid soils used in these studies, or improve alfalfa growth or plant nutrient concentration in the greenhouse leaching experiment or in three years of field research evaluations.
Alfalfa production on stakeholder field sites.
This study was funded for three years. Site location, preparation, and seeding to establish the stands of alfalfa used the first nine months of the funded period. After the following two seasons of production, alfalfa was managed for an additional two years to evaluate its stand sustainability over four years. Alfalfa continued to produce acceptable hay yields during these four production seasons, demonstrating that, with proper site selection and treatment, it is a viable forage crop on Coastal Plain soils.
Alfalfa production evaluations were located on stakeholder ranches in Gregg, Cherokee, Anderson, and Smith counties on the Griffin, Taylor (now owned by Threlkeld), Riley, and 7P Ranches, respectively. Alfalfa established on the Kilgore College Farm in Rusk County succumbed to wet soil the second season.
Alfalfa weevil infestations were an annual occurrence. Normally, scouting for weevil larva chewing damage began about mid-February. During one unusually mild winter, weevil infestations occurred in late December and had to be controlled using labeled insecticides. Weevil was easily controlled using Sevin XLR Plus (Carbaryl) or Fury insecticides. During normal winters, chemical controls were applied when chewing damage occurred on 40% of stems. Mild bleaching of leaves occurred due to use of Sevin XLR Plus for weevil control on alfalfa seedlings. Aphids invaded the alfalfa in early spring but chemical controls were not needed because ladybeetle larva and adults kept them under control. The larval stage of the ladybeetle helped control late emerging weevil larva. Varying intensities of alfalfa leafhopper infestations occurred in late spring to early summer, but needed control on only one stakeholder ranch. The alfalfa leafhopper was easily controlled using Carbaryl, although Malathion also would control these insects.
Four-year total yield was highest on the 7P Ranch where the average was slightly more than 5 tons/acre/year for both varieties. Alfalfa yield on the Griffin Ranch followed closely averaging 4.8 tons/acre for Amerigraze 702 and 4.5 tons/acre for GrazeKing. Yield was similar between varieties on the Taylor and Riley Ranches. When averaged over all sites and years, the four-year total hay yield for GrazeKing was 17.9 tons/acre and for Amerigraze 702 was 18.2 tons/acre.
After four years in production, the Amerigraze 702 variety consistently maintained a better stand than did GrazeKing. The percentage cover near harvest time on the Taylor and Riley ranches and the percent of crowns touching a 300 foot tape at 20 foot intervals on the 7P and Griffin ranches indicated approximately 50%, or greater, stand remaining for Amerigraze 702 with a range of 47% stand on the Griffin ranch to 76% on the Taylor ranch. The percentage stand remaining for GrazeKing ranged from a low of 13% on a wetter side of the field on the Griffin ranch to 64% on the Taylor ranch. Amerigraze 702 has a dormancy rating of 7 and GrazeKing is a dormancy rating 5. Both varieties appear to be well adapted to conditions around Overton, TX, and should do well across the Coastal Plain.
The Bowie soil (loamy, siliceous, semiactive, thermic Plinthic Paleudult) on the Taylor and Seven-P ranches is an excellent soil for alfalfa production. The Kirvin soil (mixed, semiactive, thermic Typic Hapludult) on the Griffin Ranch also produced good yields because the subsoil pH levels were well above 5.5 to 4-ft deep. Kirvin is a more highly leached soil than is the Trawick (mixed, active, thermic Mollic Hapludalf) on the Riley ranch. The Trawick is a red, well-drained soil with higher clay content and base saturation than other soils in this study. The Trawick subsoil pH was marginal near 5.4 to 5.5. This site was adequate, but did not produce alfalfa as well as the Bowie and Kirvin soils, primarily due to delays in harvesting and several extended grazing periods that limited the number of harvests.
The 7P Ranch continued to have the best, most weed-free stand of alfalfa after four production seasons. This was primarily due to timely removal of the previous grass crop during the summer preceding alfalfa planting in fall. At locations where less than adequate termination of the grass was accomplished, bermudagrass invasion of the alfalfa stand during the second and following production seasons was a problem that could not be overcome by use of herbicides currently labeled for grass control in standing alfalfa. Other weeds that were difficult to control in alfalfa included dock and pigweed. Poast used at label rates for control of other broadleaf weeds in late winter did not control dock, and the pigweed emerged over an extended period.
Evaluation of grazing-tolerant alfalfa varieties.
The initial DM evaluations of the six selected alfalfa varieties were as hay production. The total DM yields from one harvest in 1998 and two in 1999 showed a significant (P<.05) hay production advantage for Cimarron 3I over all other varieties with the exception of GrazeKing during the initial establishment period. The total DM production from Cimarron 3I represented about 4 tons/ac on a hay-equivalent basis. Stand of all varieties was rated as good to excellent at initiation of grazing. The height of alfalfa after about 3 week’s regrowth (5-25 to 6-16) was about 9 inches and ranged from 10-inches for Amerigraze 702 to 7.8-inches for Alfagraze. Before initiation of the stocking treatments, there was a relatively uniform stand across the varieties at about 3.8 plants per ft2 with nearly 12 stems (tillers) per plant. At the time of these 3-week regrowth measurements, estimates of forage mass ranged from about 660 lbs/ac for Alfagraze to about 900 lbs/ac for Amerigraze 401+Z and Hay Grazer.
On Nov. 5 and 6, 2001, final plot readings for plant count, stems per plant, stand height, and percent stand were conducted. The effect of stocking treatment averaged across varieties showed a near complete loss of stand with 1.3% survival when alfalfa was continuous stocked. Rotational stocking when plants reached Stage 3 resulted in 9% stand survival and rotational stocking when plants reached Stage 5 resulted in a 37% stand survival after three years grazing. The Stage 5 – Rotational stocking which mimicked hay harvest defoliation frequencies was the most conducive stocking method for sustainable alfalfa stands on Coastal Plains soils. The variability among varieties and replications allowed for moderately large standard deviations for all measurement parameters. Other plant descriptive data taken from the exact location at initiation of the experiment was also indicative of stand loss differences in stocking method. When alfalfa varieties were evaluated for percent stand, plant height, plant density, and tillering across stocking treatments, less than 25% stand was recorded for all varieties when averaged across stocking methods. Variation among measurement sites was again responsible for the magnitude of standard deviation for all measured parameters.
An examination of percent stand and plant descriptors for alfalfa varieties by stocking method provided a more detailed examination of sustainability of alfalfa under stocking regimens. Alfalfa varieties that were continuously stocked during the 3-year period, showed less than a 3% stand remaining across all varieties. Percent stand of each plot was appraised visually by two individuals, whereas all plant descriptors were taken from the exact location as the initial, pre-stocking, measurements. Plant descriptive information showed a complete loss of stand for both Amerigraze 401+Z and Cimarron 3I. However, with the very low percent stand and plants per square foot, continuous stocking led to complete destruction of all alfalfa varieties on the sandy, Coastal Plains soils.
When the selected alfalfa varieties were rotationally stocked as plants attained Stage 3 regrowth, percent stand was substantially improved and ranged from 2.7% for HayGrazer to 21.9% for Amerigraze 702. This stand survival for Amerigraze 702 was equivalent to 0.7 plants per ft2 or about 1 plant per 1.4 ft2. Alfagraze with 11% stand was second ranked in terms of sustainability under Stage 3 – Rotational stocked, and was followed by Amerigraze 401+Z and Cimarron 3I with 7% survival. GrazeKing had less than 5% stand remaining and ranked next to last among the six varieties.
Sustainability and percent stand of alfalfa was significantly improved using a Stage 5 – Rotational stocking method of defoliation via grazing. All six varieties had at least one-third stand remaining with relatively similar sustainability among all except for Amerigraze 702 with a 46% stand survival. Plant descriptor data showed about 1 plant per ft2 for both Alfagraze and Amerigraze 702, 0.7 plants per ft2 for both GrazeKing and HayGrazer, and 0.5 plants per ft2 for both Amerigraze 401+Z and Cimarron 3I. Standard deviation indicated substantial variability among plots, reps, and blocks.
The most detrimental factors contributing to significant stand loss during this grazing experiment were lack of tolerance to defoliation severity, summer drought, and the invasion of common bermudagrass. By nature of the graze-deferred treatment of rotational stocking when plants reached Stage 5, the alfalfa canopy reduced the extent of plot invasion by bermudagrass. In addition, root development was likely enhanced and stimulated plant survival. However, with the best survival rate of 50% for Amerigraze 702 under Stage 5 – Rotational stocked, forage removal via exclusive grazing is likely not the best choice for sustainable alfalfa on these soil types.
Beef cattle performance on grazed alfalfa.
Weather was near ideal for establishment of alfalfa in the winter of 1999/2000, which was unusually dry for the region. The following winter was unusually wet, which probably contributed to steady linear decline of alfalfa stands over time as measured by both crown and stem counts. The proportion of alfalfa in the available forage was 100% in 2000 and before rotation began in 2001, but averaged only 73.5% across the rotationally stocked period in 2001, with a low of 47.0% in mid-July. The balance of available forage was bermudagrass, annual ryegrass (Lolium multiflorum Lam.), and palatable weeds. Large areas of total stand loss were visually estimated at 40 to 50% of total pasture area by the end of the 2001 grazing season, primarily in low spots where water pooled or where subsurface water seepage occurred on slopes.
Alfalfa stands thinned quickly. After two years of grazing, both crown and stem densities were lower than in previous reports of grazed alfalfa (Hoveland et al., 1988; Smith et al., 1989; Bouton and Gates, 2003). Proponents have stated that that alfalfa can produce acceptable beef cattle gains at plant densities as low as 1 crown/ft2. The study pastures would be below this density by the projected start date of a third grazing season if stand thinning were to continue at the linear rate measured through the first two seasons. Smith et al. (1989) suggested that stem density is a better indicator of alfalfa productivity for grazing than is crown density. Stem density decreased more sharply across our study period than did crown density and reached a low of 26/ft2 after two seasons of grazing. This occurred despite our use of rotational stocking for most of the alfalfa-grazing period, which should improve stand survival over continuous stocking (Bouton and Gates, 2003). Others also have reported short stand life of alfalfa in the Southern plains region (Morris et al., 1992).
Available forage DMY and forage allowance per calf per day were higher for bermudagrass than for alfalfa throughout the 2000 grazing period, with an interaction between treatment and time (P < 0.001) related primarily to changes in the magnitude of the difference. In 2001, a crossover interaction occurred between treatment and time (P < 0.001), in which forage DMY and allowance were greater for alfalfa than bermudagrass up to the initiation of rotational stocking during the week of May 7, but usually less than bermudagrass after July 1. Cumulative forage yield over the entire season was much greater for bermudagrass than for alfalfa. Maximum IGR was similar for both pasture species, but alfalfa had more of its growth early in the season than bermudagrass. The inflection point at which IGR began to decline was earlier for alfalfa than for bermudagrass in both years. Alfalfa went dormant due to dry periods during August in both years, necessitating cattle removal from pastures due to lack of forage. Alfalfa broke summer dormancy when cool fall weather and rain returned, but did not accumulate useable amounts of forage in fall 2000. In 2001, alfalfa pasture accumulated 6012 lb/acre of available forage by Nov. 14, allowing a post-frost grazing for 10 days at 6.5 animal units/acre (1000 lb live weight).
Alfalfa DM available for grazing was similar to yields reported for alfalfa cut at four to six week intervals in Georgia (Hoveland et al., 1996). In addition to summer forage, alfalfa provided two hay cuttings in spring the seedling year and 65 animal unit grazing days/acre on frost aftermath in 2001. Alfalfa produced most of its growth earlier in the season than bermudagrass. The good spring growth potential of alfalfa was expected, but its poor late summer growth was not. Alfalfa went dormant in August each year exactly at the time it was hypothesized its deeper root system would give it a competitive advantage over more shallow- rooted bermudagrass. When alfalfa went dormant in summer, it dropped its leaves and presented no useful stockpiled forage. Unusually wet conditions throughout much of the study period coupled with subsoil acidity, Al toxicity, or presence of a fragipan may have contributed to a shallow root system that prevented alfalfa from demonstrating the drought tolerance expected. Hoveland et al. (1988) reported that the alfalfa-grazing season could be truncated by drought in Georgia. The predominantly wet soil conditions probably contributed a great deal to stand decline.
Patterns of DMY followed expected trends for bermudagrass, which as a warm-season plant, should reach maximum IGR later in the season than cool-season plants (Belesky et al., 2002). Bermudagrass pastures accumulated a great amount of standing biomass in summer, especially in 2001. This was attributed to the tendency of bermudagrass to regrow primarily from upper nodes on grazed stubble and the refusal of calves to graze below this upper leafy layer, resulting in accumulation of ungrazed stemmy material with each rotation. Wilkinson et al. (1970) reported that bermudagrass swards were higher in quality in top layers, but that most of the DMY was in the lower layers. In a different management system, this problem might be remedied by following the initial grazing of stocker calves with grazing by adult cattle to clean up the low-quality stubble. The accumulated stubble did provide “stockpiled,” albeit low quality, forage that held calves through periods of slow bermudagrass growth in August without the need for supplementation, but ADG was low during these periods.
Interactions between forage treatment and time within grazing season were observed for NDF, ADF, and CP in both years (P < 0.001). These were related to changing rank of treatments in 2000 and to treatments differences in the rate of change over time in 2001. Alfalfa was consistently the same or higher in CP than bermudagrass throughout the trial. Alfalfa was lower in NDF than bermudagrass in both years. Forage ADF levels were similar for both treatments in 2000, but greater for alfalfa than for bermudagrass in 2001.
Regression analysis revealed no pattern to forage quality values across the short 2000 grazing season. In 2001, alfalfa forage quality dropped across the early part of the grazing season as pastures were gradually being subdivided into rotation paddocks. During the rotational management time period, NDF and ADF increased while CP decreased linearly over time. Bermudagrass pastures exhibited the same general trend, but with a curvilinear pattern for fiber components. Bermudagrass CP decreased linearly over the season, with small imbedded peaks corresponding to N fertilization events in May and June.
In general, fluctuations in forage quality from week to week were less for bermudagrass than for alfalfa, and bermudagrass changed less in quality over the entire season. While alfalfa was consistently higher in CP than bermudagrass, it was also always higher in NDF and often higher in ADF than bermudagrass. Hermann et al. (2002) reported similar NDF concentrations for grazed alfalfa in Iowa, but our maximum season CP concentrations were 30% compared to their 22%. Hermann et al. (2002) also reported that NDF content increased over the grazing season while CP and in vitro DM degradability (IVDMD) decreased, but they did not find an effect of time on ADF concentration. Bermudagrass NDF and ADF were within reported ranges for clipped (Mandebvu et al., 1999) or grazed forage (Mathews et al., 1994), while bermudagrass CP was generally similar to (Mathews et al., 1994; Mandebvu et al., 1999) or greater than (Griffin and Watson, 1982) reported values. Relatively high levels of CP in bermudagrass were likely related to the N fertilization program, since patterns in the CP concentration over the grazing season reflect fertilization dates. In a review, Van Keuren and Matches (1988) stated that energy is more likely than CP to limit animal performance on alfalfa pasture. Similar statements have been made regarding warm-season grass pastures. Forage ADF is generally accepted as an indicator of forage digestibility and energy content, so the relatively high ADF content of alfalfa compared to bermudagrass suggests energy may have been more limiting on alfalfa pastures.
There was little difference in end-of-season calf performance between pasture treatments. In 2000, pasture treatment did not significantly influence heifer final weight, average daily gain (ADG), or gain per acre. In 2001, calves grazing alfalfa tended (P < 0.06) to have higher ADG than calves grazing bermudagrass, but this was not reflected in better total gain per acre. No calves bloated at any time during the trial, nor was there mortality from other causes on either treatment. The pattern of calf performance across the grazing season was different between treatments. Calf full body weight (FBW) was higher for calves pastured on alfalfa than on bermudagrass at every measurement date in 2000, but only on one date in 2001. However, cumulative gain per acre was higher on alfalfa than on bermudagrass on every date except one over both years, despite negative ADG by cattle on both treatments from mid May to mid-June 2001 and on bermudagrass in August 2001.
Individual animal ADG on alfalfa was within the range of 0.79 to 1.94 lb/day reported in Georgia (Hoveland et al., 1988; Bates et al., 1996), but less than ADG reported in Michigan (Schlegel et al., 2000). Gain per acre on alfalfa was similar to the Georgia results (Hoveland et al., 1988; Bates et al., 1996) in 2000 but greater in 2001. On bermudagrass, gain per acre and ADG were lower than reported values (Utley et al., 1974; Greene et al., 1990). Forage allowances on alfalfa were similar to those reported by Hoveland et al (1988). During the rotational stocking periods, forage allowance per calf per day averaged 32 lb DM for alfalfa and 51 lb DM for bermudagrass in 2000, and 19 and 31 lb DM in 2001. Allowances were higher during continuously stocked periods. The relatively lower forage allowance for alfalfa in 2001 was the result of high stocking densities used in an effort to encourage calves to graze alfalfa to the target stubble height of 2 inches. Stocker calves readily grazed alfalfa to the target height during the spring when stands were leafy and lush, but refused to eat stems in summer, resulting in wastage of a large part of the forage allowance. The problem was exacerbated with each rotation cycle because the tall stubble allowed alfalfa regrowth to originate from stem rather than crown buds, a situation that is detrimental to both alfalfa DMY and stand persistence. Because calves trampled the stems flush to the ground, the problem could not be remedied by mowing of exit paddocks.
The most noticeable difference between forages was in grazing days. Bermudagrass pastures provided a longer grazing season for stocker calves (days on pasture), more grazing days, and more calf-grazing days than alfalfa pastures in both years. There were more hay feeding days for alfalfa pastures in 2000 and more for bermudagrass pastures in 2001. Because calves grazing alfalfa had to be removed from pastures several times per season due to muddy conditions, pesticide withdrawal periods, or brief periods of forage shortage, bermudagrass pastures provided more calendar days of grazing, more animal grazing days, and an uninterrupted grazing period once calves were turned onto pastures, even though bermudagrass grazing began three weeks later in 2001 than for alfalfa. However, total gain per acre for the season was not different between pasture types, indicating that calves grazed on alfalfa could make the same amount of gain in less time than calves grazing bermudagrass.
Direct comparison of the two pasture systems was difficult because they were very different in management requirements. In general, alfalfa pastures required more frequent management attention and were less tolerant of disruptions in the grazing rotation. Such disruptions were caused by pesticide grazing restrictions and muddy conditions that forced cattle to be removed from pastures to prevent excessive trampling damage. Because of the rapid maturation of alfalfa and its tendency to drop its leaves in summer once flowering began, delays in grazing paddocks resulted in stemmy forage with poor acceptability to the calves. In contrast, bermudagrass rotations were never interrupted for any reason once grazing commenced each season.
Summer weed control was the most troublesome of the management concerns that interfered with timely utilization of alfalfa paddocks. Spiny pigweed and horse nettle formed dense patches that were not consumed to any great extent by calves even under heavy grazing pressure. Poor residual control of pigweed seedlings that emerged continuously during the summer limited the usefulness of imazethpyr, and its long grazing restriction resulted in over-maturation of paddocks before cattle could re-enter. Mowing alfalfa paddocks after grazing provided some weed control, but was required after every occupation period because weeds exhibited vigorous regrowth after clipping. Horse nettle and pigweed also occurred in the bermudagrass pastures but were readily controlled with 2,4-D plus picloram, which do not have a grazing restriction for beef cattle.
Scouting for insect pests was the most time-consuming management activity throughout the alfalfa-growing season. Pea aphids and alfalfa weevils were present each spring, but did not require chemical control. However, three-cornered alfalfa leafhopper caused substantial yield and forage quality loss each summer by girdling stems and causing alfalfa to drop its lower leaves. Insecticide provided only short-term relief and grazing restrictions interfered with timely use of paddocks in the same way. Three-cornered leafhoppers have caused extensive alfalfa crop loss in southern regions (Sorenson et al., 1988). Insect pests were not a concern on bermudagrass pastures.
Biochemical analyses of gypsum treated and fertilized alfalfa
Effects of amendments on hexose and protein contents. In the absence of B, gypsum treatments progressively decreased the alfalfa total protein but increased the hexose content. In the absence of gypsum, B at 0.15 g m-2 increased the hexose content, but decreased the hexose content at the higher rate without affecting the protein contents. Boron at 0.15 g m-2 without gypsum increased the hexose by about 15%, but addition of gypsum decreased the hexose level. The 0.15 g B decreased the total protein with or without gypsum treatment thereby demonstrating the independent ability of B to detoxify the soil Al. Boron at 0.3 g m-2 together with 0.5 kg gypsum m-2 decreased the alfalfa total protein level, but together with 1 kg m-2 gypsum, it increased the protein by about 4% compared with the control (without B and gypsum). Boron at 0.45 g m-2 together with 0.5 kg m-2 of gypsum did not affect the alfalfa protein level, but with or without 1 kg of gypsum, it induced a 14% decrease in the protein level thereby suggesting that B and Ca did not synergistically detoxify the Al. Gypsum without B and limestone decreased the alfalfa protein content by about 25% thus confirming its independent ability to detoxify the soil Al. Therefore, B and gypsum exerted independent effects on the alfalfa protein contents but antagonistic effects on the hexose contents thereby making it difficult to identify the endpoint of the neutralization of Al toxicity through the combined application of B and Ca.
Effects of serial harvesting on hexose contents. Neither the sludge, nor the gypsum treatments significantly changed the hexose contents of the harvest 1 as compared to the control alfalfa. However, in harvest 2, the high sludge treatment increased the hexose content by about 7%, while the high gypsum treatment decreased the hexose content by about14% relative to the control.
Effects of serial harvesting on protein contents. Neither the calcium sulfite sludge nor the gypsum amendments significantly reduce the soluble protein contents of the alfalfa. This is similar to the response of the hexose level to the soil amendments. In the second harvest, the protein levels of the treated alfalfa were 10-69% higher than the control. On the sustainability of alfalfa production, the protein levels of the second harvest were 24-54% lower than in the first harvest. Alfalfa forage nitrogen declined yearly in a 5-year harvest study (Raun et al. 1999), and the root nitrogen reserve similarly declined after the first harvest (Dhont et al. 2003). However, the protein levels of the third harvest with and without soil amendments then increased (32-154%) although the trends in the increases did not correspond to the rates of the amendments applied to the soil. Therefore, the demonstrated sustainability and re-growth persistence on the acid soil was not due to the amendments. However, in the fourth harvest, the protein levels of the gypsum-amended alfalfa declined (6.4-11.5%) while those of the sludge amendments and the control continued to increase (5.1-95.4%).
Effects of amendments on chlorophyll contents. Increases in gypsum rates at fixed B rates generally increased the chlorophyll (chl) contents. Boron at 0.45 g m-2, and gypsum at 0.5 kg m-2 gave the highest increase (about 30%) in chl as compared to the control.
Effects of serial harvesting on chlorophyll contents. The control alfalfa had 35.7 mg chl/g, but the low sludge, medium sludge, and high gypsum amendments decreased the total chl contents by up to 27.8% in the first harvest. The medium gypsum treatment increased the chl content by about 27%, whilst the other treatments did not induce significant changes in the chl contents. The changes in the chl contents were accompanied by moderate changes ranging from 5-8 in the chl a to chl b ratios. In the second harvest, the physiological effects of the amendments had become visible because all the treatments induced higher chl contents (up to about 69% increase).
Effects of amendments on GDH oxidoreductase activity. GDH oxidation: reduction ratios were generally less than 1 except in the 1 kg gypsum treatment without B. The alfalfa with the high (1.71) GDH oxidation: reduction ratio also had about 25% higher chl content (17.6 g/kg) and correspondingly about 20% higher hexose content (1.13 g kg-1), but about 36% lower protein content (24.3 g kg-1) than the control alfalfa. These results show that the oxidative and reductive components of GDH are functionally interdependent, in agreement with the roles ascribed to its oxidative activity in carbon metabolism (Aubert et al. 2001, Robinson et al. 1991, Srivastava and Singh 1987).
Effects of serial harvesting on GDH oxidoreductase activity. GDH oxidation: reduction ratios were less than 1 in the first alfalfa harvest. However, the trends in the oxidoreductase activity did not correspond with the trend in the quantities of amendments applied to the soil. Thereafter the oxidoreductase activity progressively increased and in the third harvest, most of the activity had exceeded 1. Therefore, the enzyme became more oxidative in response to the successive harvests. These results show that the oxidative and reductive components of GDH are functionally interdependent, in agreement with the roles ascribed to its oxidative activity in carbon metabolism (Aubert et al. 2001; Robinson et al. 1991; Srivastava and Singh 1987).
Effects of amendments on fructose 1,6-Bisphosphatase activity. Boron at 0.15 g m-2 in the absence of gypsum induced a good (96%) increase in the FBPase activity. However, increasing the rates of B in the absence of gypsum and also at 0.5 kg m-2 gypsum decreased the FBPase activity by about 37% and 69%, respectively. Similarly, increasing the rates of gypsum at fixed moderate rates of 0.15 and 0.3 g m-2 B decreased the FBPase activity by 53% and about 31% respectively. However, increasing the rates of B at higher fixed gypsum (1 kg m-2) rate alleviated the Ca-B antagonism because the FBPase activity increased (about 91%).
Effects of amendments on the RNA synthetic activity of GDH. Gypsum at 0.5 kg m-2 in the absence of B increased the RNA synthetic activity of GDH by about 25%. Also in the absence of gypsum, increasing the rates of B to 0.45 g m-2 increased the RNA synthetic activity of GDH. However, increasing the rates of B at fixed rates of 0.5 and 1.0 kg m-2 gypsum decreased the RNA synthetic activity of GDH by about 48%, and 55%, respectively. This contrasted the FBPase activity that increased in the 1.0 kg m-2 fixed gypsum with increasing B rates. In addition, increasing the rates of gypsum at fixed rates of 0.3 and 0.45 g m-2 B decreased the RNA synthetic activity of GDH by about 41%, and 63% respectively. In the absence of B, 1.0 kg m-2 gypsum increased the RNA synthetic activity of GDH by about 32% when limestone was withheld, thus showing that excessive Ca is detrimental to RNA synthetic activity of GDH when B is deficient. Therefore, by responding systematically to the full spectrum of the multi-factorial B, and gypsum amendments of soil, the RNA synthetic activity of GDH was more robust than the FBPase activity (Osuji et al. 2004).
Effects of serial harvesting on the RNA synthetic activity of GDH. The low sludge amendment increased the RNA synthetic activity of GDH by about 27% in the first harvest. All the other amendments decreased the RNA synthetic activity of GDH in the first harvest, the higher the rate of the amendment the lower was the activity of the enzyme. Therefore, GDH systematically responded to the effects of the amendments even as early as in the first harvest. The hexose, protein, and chl levels were insensitive to the effects of the amendments at the first harvest.
Effect of amendments on free nucleotides. Boron at 0.15 g m-2 in the absence of gypsum, or gypsum at 0.5 kg m-2 in the absence of B decreased the free nucleotide concentration by 40% and 57%, respectively. In addition, increasing the rates of B in the presence of 0.5 kg m-2 gypsum decreased the concentrations of free nucleotides. However, increasing the rates of B at higher fixed gypsum (1.0 kg m-2) rate increased the concentration of the free nucleotides. Therefore the free nucleotides and the FBPase activity responded similarly to the soil amendments thereby confirming that the point of inflection at 1.0 kg m-2 gypsum marked the endpoint of the neutralization of the soil acidity by the gypsum and limestone.
Effects of serial harvesting on fructose 1,6-bisphosphatase activity. Apart from a few exceptions, there was a general trend of decline in FBPase activity in the successive harvests. There was no change in activity in the harvests from the medium sludge amendment. Similarly, there were no significant changes from the first to the second harvest thus suggesting that the enzyme was initially insensitive to the soil amendments. But from the second to the third harvest in the high gypsum amendment, the FBPase suffered about 29% loss in activity even though the total chlorophyll increased by only 9%. From the third to the fourth harvest in the high sludge amendment, the FBPase suffered about12% loss in activity even though there was no change in total chlorophyll content. Therefore, the FBPase reacted adversely to the serial harvesting of alfalfa unlike the RNA synthetic activity of GDH that robustly persisted and differentially increased in activity during the serial harvests. FBPase catalyzes the irreversible hydrolysis of fructose 1,6-bisphosphate to fructose 6-phosphate and Pi in the synthesis of sucrose, and in so doing it transduces light energy in the Calvin cycle at the interface between electron transport and product synthesis (Buchanan 1980). It is regulated by Ca2+ (Kreimer et al. 1988). It was therefore possible that the FBPase suffered from the Ca-Al antagonism arising from the soil Al and the Ca contents of the sludge, limestone, and gypsum. FBPase was therefore inadequate for assessing the sustainability of alfalfa production on the Ca-amended Coastal Plain soil.
Educational & Outreach Activities
A planning meeting with stakeholder cooperators was held at the beginning of this project to discuss alfalfa establishment and production on field sites. Annual field days were conducted on producer alfalfa sites to discuss alfalfa production on Coastal Plain soils. Results of field trials were printed in the Texas Agricultural Experiment Station 1992 and 19994 field day reports published and released at Texas A&M-Overton. Presentations on alfalfa production continue to be requested by clientele groups. Two journal papers are in process from the biochemical analysis studies. Other journal papers are planned for the field studies. Abstracts and poster papers have been presented and others are planned for presentation at ASA, CSSA, and SSSA annual meetings and at the International Grassland Congress. A refereed journal paper was presented on site selection, soil testing, and fertilization for alfalfa production on Coastal Plain soils at the International Symposium on Soil and Plant Analysis held in South Africa. This paper is in press for a special issue of Communications in Soil and Plant Analysis. A paper on animal response to grazing alfalfa was presented at the American Forage and Grassland Council annual meeting and was published in the proceedings of this meeting. Guidelines for production of alfalfa on Coastal Plain soils are available at http://overton.tamu.edu or http://soils.tamu.edu
The multiple studies funded in this USDA-SARE project greatly increased the knowledge gathering needed for determining successful production of alfalfa on the US Coastal Plain. The neutralization of phytotoxic levels of subsoil aluminum in strongly acidic soils by use of gypsum will be a lengthy process in Coastal Plain soils. Beef cattle weight gains were increased by grazing alfalfa compared to common bermudagrass, but the level of management required for a grazing alfalfa is greatly increased compared to common bermudagrass.
Alfalfa production on stakeholder ranches on three selected Coastal Plain soils was sustainable over four growing seasons, and some sites had sufficient stand densities to continue into a fifth hay production season. This verified the site selection criteria developed in our small-plot research studies on differing Coastal Plain soil types. Economic analysis of stakeholder alfalfa production verified economic projections made for alfalfa production on small plots. Alfalfa on the 7P ranch produced a net return of over $1,200 for the four seasons of production. The next highest net return was $247 per acre annually for the four years of production. Even the lowest annual net return of $129 per acre exceeds the net return of Coastal Bermudagrass hay production estimated to range from $30 to $60 per acre annually.
Perhaps the most valuable biological and economic impact of the stocking experiment is that alfalfa should not be continuous stocked on Coastal Plain soils in the southeastern US. Further, continuous stocking of alfalfa is likely not the best management practice for commercial grazing operations irrespective of climatic-geographical region in the US. Van Keuren and Matches (1988) suggested that alfalfa production is best under defoliation regimens that allow for periods of deferment such as hay making or rotational grazing. In addition, Bouton and Smith (1998) submitted a standard test that relies on continuous stocking to evaluate alfalfa cultivars for grazing tolerance. However, they pointed out that this research methodology was not intended to be used in commercial stocking-livestock production ventures. Bouton and Gates (2003) suggested that under both grazing and hay defoliation regimens, commercial ventures should select grazing tolerant alfalfa cultivars for enhanced sustainability and production.
Demonstrable impacts for the future from this stocking experiment on alfalfa will be targeted at commercial operations that incorporate multi-use harvesting of alfalfa via rotational stocking during spring and fall with hay harvests as warranted during the summer months. In addition, additional alfalfa germplasm evaluations under stocking conditions will be necessary to release a cultivar with extended persistence and sustainability on coastal Plain soils in the southern US.
Records of all production inputs, farm operations, and yield estimates from alfalfa production on stakeholder ranches were maintained for economic analysis. The largest input cost was for limestone on sites where an adequate liming program previously had been poorly maintained. Expenses for establishment included soil sample analysis of the surface 6-in depth for pH and residual available plant nutrients and one-foot depths from the surface to 48 inches for pH and exchangeable aluminum. Other included expenses were for fertilizer, disking to remove existing vegetation, to incorporate limestone and fertilizer, and for seedbed preparation, rolling to pack the soil surface and create a smooth seedbed, fencing, and pest control. Establishment costs on a per acre basis were $232.28 on the Griffin ranch, $252.63 on the 7P ranch, $326.13 on the Taylor ranch, $352.65 on the Riley ranch, and $251 on the Kilgore College Farm. For the annual economic evaluations, establishment costs were prorated over four years.
Production expenses included blended fertilizer and its application, pesticides and application costs, machinery maintenance, custom hay harvesting and hauling, interest on production capital, and overhead on machinery and equipment and land. Over four years these production expenses were $1,358.70 on the Griffin ranch, $1,406.11 on the 7P ranch, $1,336.35 on the Taylor ranch, and $1,395.04 on the Riley ranch. For two years, the production expenses on the Kilgore College farm amounted to $800.31.
Alfalfa yield estimates were based on the one meter-square quadrat samples collected just prior to hay harvest or grazing of the alfalfa regrowth occurred. These yield samples were oven dried, weighed, and adjusted to 12% moisture. Yield estimates collected in this manner proved to be very close to the actual yields obtained by these stakeholders when they baled the alfalfa for hay. The four-year net return per acre on alfalfa valued at $135 per ton was $988.91 on the Griffin ranch, $1,206.04 on the 7P ranch, $894.66 on the Taylor ranch, and $517.68 on the Riley ranch. Even with stand termination on the Kilgore College farm in the second season, net income was $124.44 per acre. On ranches where alfalfa production continued through four years, annual net income per acre was $247.23 on the Griffin ranch, $301.51 on the 7P ranch, $223.67 on the Taylor ranch, and $129.42 on the Riley ranch. Alfalfa stands on the four-year sites were adequate for hay production to continue for a fifth year except for the GrazeKing variety on the Griffin ranch. These results indicate the increased income potential from alfalfa hay production on Coastal Plain soils.
Production of alfalfa, whether for hay or for grazing, requires more intensive attention to management than production of bermudagrass. Many of the stakeholders on the Coastal Plain work another job to support their income from farm or ranch operations. This limits the time they have to manage production of alfalfa. Other full-time producers no longer have the necessary equipment to drill-seed alfalfa or the spraying equipment needed for pest control. The acceptance of alfalfa as a viable crop on the Coastal Plain is going to be slow, but it eventually will become a more commonly produced forage in this region. Alfalfa produced for hay is one of the most profitable agricultural crops that can be grown on Coastal Plain soils and, in addition, has the potential to pay for agricultural land.
Areas needing additional study
Weed control, especially control of common bermudagrass, dock, and pigweed needs additional study in alfalfa stands on Coastal Plain soils. More rapid methods for reducing phytotoxic levels of subsoil aluminum need to be determined. Alternative and more rapid methods for curing first-harvest alfalfa during the high rainfall, high humidity season need further study.
Aiken, G. E., S. E. Sladden, and D. I. Bransby. 1991. Yield and forage quality responses for bermudagrass mowed at different intervals and heights. Proc. Amer. Forage and Grassland Council, Columbia, MO.
Ameziane, R., K. Bernhard, and D. Lightfoot. 2000. Expression of bacterial gdhA gene encoding a NADPH glutamate dehydrogenase in tobacco affects plant growth and development. - Plant and Soil 221: 47-57.
Aubert, S., R. Bligny, R. Douce, E. Gout, R. G. Ratcliffe, and J. K. M. Roberts. 2001. Contributions of glutamate dehydrogenase to mitochondrial glutamate metabolism studied by o;C and ;oP magnetic resonance. J. Exp. Bot. 52: 37 B 45, 2001.
Bates, G.E., C.S. Hoveland, M.A. McCann, J.H. Bouton, and N.S. Hill. 1996. Plant persistence and animal performance for continuously stocked alfalfa pastures at three forage allowances. J. Prod. Agric. 9:418-429.
Beedy, T. L. 2000. Phosphorus fertilization of alfalfa on Coastal Plain soils. M.S. thesis. Texas A&M University, College Station.
Belesky, D.P., J.M. Fedders, J.M. Ruckle, and K.E. Turner. 2002. Bermudagrass-white clover-bluegrass sward production and botanical dynamics. Agron. J. 94:575-584.
Bohnsack, C. W. and L. S. Albert. 1977. The effect of boron deficiency on indoleacetic acid oxidase levels of squash root tips. Plant Physiol. 59:1047-1050.
Beedy, T. L, V. A. Haby, F. M. Hons, J. V. Davis, and A. T. Leonard. 1995. Phosphorus fertilization of alfalfa on Coastal Plain soils. Agron. Abstracts 87:252.
Bouton, J. H. and R. N. Gates. 2003. Grazing-tolerant alfalfa cultivars perform well under rotational Stocking and hay management. Agron. J. 95:1461-1464.
Bouton, J. H., S. R. Smith, Jr., D. T. Wood, C. S. Hoveland, and E. C. Brummer. 1991. Registration of ‘Alfagraze’ alfalfa. Crop Sci. 31:479.
Brown, R. H. and G. T. Byrd. 1990. Yield and botanical composition of alfalfa-bermudagrass mixtures. Agron. J. 88:573-577.
Brown, P.H., and H. Hu. 1997. Does boron play only a structural role in the growing tissues of higher plants? In: Ando, T., K. Fujita, T. Mae, H. Matsumoto, S. Mori, and J. Sekiya (ed.): Plant nutrition for sustainable food production and environment. Pp 63-67. Kluwer Academic Publishers, Dordrecht.
Buchanan, B.B. 1980. Role of light in the regulation of chloroplast enzymes. Ann. Rev. Plant Physiol. 31: 341-374.
Budavari, S. (Ed.) 1989. The Merck Index. Merck & Co., Inc. Rahway, NJ, USA.
Buol, S. W., F. D. Hole, and R. J. McCracken. 1973. Soil genesis and classification. The Iowa State University Press, Ames, Iowa.
Camacho-Cristobal, J.J., and A. Gonzalez-Fontes. 1999. Boron deficiency causes a drastic decrease in nitrate content and nitrate reductase activity, and increases the content of carbohydrates in leaves from tobacco plants. Planta 209: 528-536.
Clary, G. M. and V. A. Haby. 1998a. Potential for profits from alfalfa in East Texas. Texas Agric. Exp. Stn. Research Cntr. Tech. Rep. 1:117-118.
Clary, G. M. and V. A. Haby. 1998b. Comparison of net returns from alternative production systems for alfalfa grown on acid humid-region soils. Southern Branch Am. Soc. Agron. Abst. 25:9.
Counce, P.A., J.H. Bouton, and R.H. Brown. 1984. Screening and characterizing alfalfa for persistence under mowing and continuous grazing. Crop Sci. 24:282-285.
Dhont, C., Y. Castonguary, P. Nadeau, G. Belanger, and F. Chalifour. 2002. Alfalfa root carbohydrates and regrowth potential in response to fall harvests. Crop Sci. 42:754-765.
Dixit, D., N. K. Srivastava, and S. Sharma. 2002. Boron deficiency induced changes in translocation of 14CO2- photosynthate into primary metabolites in relation to essential oil and curcumin accumulation in turmeric (Curcuma longa L.). B Photosynthetica 40:109 -113.
Garland, W. J. and D. T. Dennis. 1977. Steady-state kinetics of glutamate dehydrogenase from P. sativum mitochondria. Arch. Biochem. Biophys. 182:614-627.
Greene, B. B., M. M. Eichhorn, W. M. Oliver, B. D. Nelson, and W. A. Young. 1990. Comparison of four hybrid bermudagrass cultivars for stocker steer production. J. Prod. Agric. 3:253-252.
Griffin, J.L., and V.H. Watson. 1982. Production and quality of four bermudagrasses as influenced by rainfall patterns. Agron. J. 74:1044-1047.
Haby, V. A., J. V. Davis, and A. T. Leonard. 1998. Alfalfa response to boron at variable soil pH on Coastal Plain soils. Better Crops with Plant Food No. 1:22-23.
Haby, V. A., R. H. Loeppert, R. Villavicencio, A. T. Leonard, and J. V. Davis. 1995. Limestone efficiency and boron effects on forage yield and soil properties. p. 505-510. In R. A. Date et al., (Eds.) Plant Soil Interactions at Low pH. Kluwer Publishers.
Haby, V. A., F. M. Rouquette, Jr., J. V. Davis, A. T. Leonard, G. W. Evers, F. M. Hons, and S. A. Reeves. 1997. Alfalfa production on acid humid-region soils. Amer. Forage and Grassland Council Proceedings 6:64-67.
Havlin, J. L. and P. N. Soltanpour. 1980. A nitric acid plant tissue digest method for use with inductively coupled plasma spectrometry. Commun. Soil Sci. Plant Anal. 11(10):969-980.
Hermann, M. L., J. R. Russell, and S.K. Barnhart. 2002. Evaluation of hay-type and grazing-tolerant alfalfa cultivars in season-long or complementary rotational stocking systems for beef cows. J. Anim. Sci. 80:768-779.
Heyes, J.A., P. J. White, and B. C. Loughman. 1991. The role of boron in some membrane characteristics of plant cells and protoplasts. In: Randall, D.D., Blevins, D.G., Miles, C.D. (ed.): Current topics in plant biochemistry and physiology. 10:179 -194. University of Missouri interdisciplinary plant biochemistry and physiology program, Columbia.
Horst, W.J., N. Schmohl, M. Kollmeier, F. Baluska, and M. Sivaguru. 1999. Does aluminum affect root growth of maize through interaction with the cell wall – plasma membrane – cytoskeleton? Plant Soil 215:163-174.
Hoveland, C.S., R.G. Durham, and J.H. Bouton. 1996. Weed encroachment in established alfalfa as affected by cutting frequency. J. Prod . Agric. 9:399-402.
Hoveland, C. S., N. S. Hill, R. S. Lowrey Jr., S. L. Fales, M. E. McCormick, and A. E. Smith Jr. 1988. Steer performance on birdsfoot trefoil and alfalfa pasture in central Georgia USA. J. Prod. Agric. 1:343-346.
Hoyt, P. B. and M. Nyborg. 1972. Use of dilute calcium chloride for the extraction of plant-available aluminum and manganese from acid soil. Can. J. Soil Sci. 52:163-167.
Hu, H., S. G. Penn, C. B. Lebrilla, and P. H. Brown. 1997. Isolation and characterization of soluble boron complexes in higher plants. Plant Physiol. 113:649-655.
Huang, J.W., J. E. Shaff, D. L. Grunes, and L. V. Kochian. 1992. Aluminum effects on calcium fluxes at the root apex of aluminum-tolerant and aluminum-sensitive wheat cultivars. Plant Physiol. 98: 230-237.
Isaac, R.A. 1990. Plants. In: Helrich, K. (ed.): Official Methods of Analysis AOAC. Pp. 40-68. AOAC Publishers, Arlington, VA.
Johnson, S. L. and K. W. Smith. 1976. The interaction of borate and sulfite with pyridine nucleotides. Biochemistry 15: 553-559.
Kreimer, G., M. Melkonian, M., J. A. M. Holtum, and E. Latzko. 1988. Stromal free calcium concentration and light- mediated activation of chloroplast fructose-1,6-bisphosphatase.- Plant Physiol. 86: 423 B 428.
Leegood, R. C. 1990. Enzymes of the Calvin cycle. In Methods in Plant Biochemistry. Lea, P. J. (Eds.) Vol 3. p. 15-37. Academic Press, New York.
Loyola-Vargas, V. M. and E. S. De Jimenez. Differential role of glutamate dehydrogenase in nitrogen metabolism of maize tissues. Plant Physiol. 76:536-540.
Ma, J. F., S. J. Zheng, and H. Matsumoto. 1997. Secretion of citric acid as an aluminium-resistant mechanism in Cassia tora L. In: Ando, T., K. Fujita, T. Mae, H. Matsumoto, S. Mori, and J. Sekiya, 1997. (ed.). Plant nutrition for sustainable food production and environment. Pp. 449-450. Kluwer Academic Publishers, Dordrecht.
Mahboobi, H. and M. Yucel. 2002. Changes in total protein profiles of barley cultivars in response to toxic boron concentration. J. Plant Nutr. 23:391-399.
Mandebvu, P., J.W. West, G.M. Hill, R.N. Gates, R.D. Hatfield, B.G. Mullinix, A.H. Parks, and A.B. Caudle. 1999. Comparison of Tifton 85 and Coastal bermudagrasses for yield, nutrient traits, intake, and digestion by growing beef steers. J. Anim. Sci. 77:1572-1586.
Mathews, B.W., L.E. Sollenberger, and C.R. Staples. 1994. Dairy heifer and bermudagrass pasture response to rotational and continuous stocking. J. Dairy Sci. 77:244-252.
Mehlich, A. 1984. Mehlich 3 soil test extractant: a modification of the Mehlich 2 extractant. Commun. Soil Sci. Plant Anal. 15(12):1409-1416.
Morris, D.E., A.G. Caldwell, and D.L. Corker. 1992. Irrigating and liming alfalfa on Coastal Plain soil. Agron. J. 84:951-955.
Oats, K. M. and A. G. Caldwell. 1985. Use of by-product gypsum to alleviate soil acidity. Soil Sci. Soc. Am. J. 49:915-918.
Osawa, H., K. Kojima, and S. Sasaki. 1997. Excretion of citrate as an aluminium-tolerance mechanism in tropical leguminous trees. In: Ando, T., K. Fujita, T. Mae, H. Matsumoto, S. Mori, and J. Sekiya. (ed.): Plant nutrition for sustainable food production and environment. Pp. 455-456. Kluwer, Academic Publishers, Dordrecht.
Osuji, G.O. and C. Braithwaite. 1999. Signaling by glutamate dehydrogenase in response to pesticide treatment and nitrogen fertilization of peanut (Arachis hypogaea L.). - J. Agric. Food Chem. 47: 3332-3344.
Osuji, G.O., C. Braithwaite, K. Fordjour, W. C. Madu, A. Beyene, P. S. Roberts, and V. Wright. 2003a. Purification of glutamate dehydrogenase isoenzymes and characterization of their substrate specificities. Prep. Biochem. Biotech. 33: 13-28.
Osuji, G. O., R. G. Cuero, and A. C. Washington. 1991. Effect of alpha-ketoglutarate on the activities of glutamate synthase, glutamate dehydrogenase, and aspertate transaminase of sweetpotato, yam tuber, and cream pea. J. Agric. Food Chem. 39:1590-1596.
Osuji, G. O., V. A. Haby, A. Beyene, W. C. Madu, and A. S. Mangaroo. 1997. The isomerization of glutamate dehydrogenase in response to lead toxicity in maize. Biol. Plant. 40:389-398.
Osuji, G. O. and W. C. Madu. 1995. Ammonium ion-dependent isomerization of glutamate dehydrogenase in relation to glutamate synthesis in maize. Phytochemistry 39:495-503.
Osuji, G. O. and W. G. Madu. 1997. Regulation of peanut glutamate dehydrogenase by methionine sulphoximine. Phytochemistry 46:817-825.
Osuji, G.O., W. C. Madu, C. Braithwaite, A. Beyene, P. S. Roberts, A. Bulgin, and V. Wright. 2003/4 Nucleotide-dependent isomerization of glutamate dehydrogenase in relation to total RNA contents of peanut. Biol. Plant. 47: 195-202.
Pasluk-Bronlkowska, W., T. Bronlkowski, and M. Ulejczyk. 1992. Mechanism and kinetics of autoxidation of calcium sulfite slurries. Environ. Sci. Technol. 26:1976-1981.
Pavin, M. A., F. T. Bingham, and P. F. Pratt. 1984. Redistribution of exchangeable calcium, magnesium, and aluminum following lime or gypsum applications to a Brazilian Oxisol. Soil Sci. Soc. Am. J. 48:33-38.
Ritchey, K. D., T. B. Kinraide, and R. R. Wendell. 1995. Interactions of calcium sulfite with soils and plants. Plant and Soil 173:329-335.
Robinson, S.A., A. Slade, G. G. Fox, R. Phillips, R. G. Ratcliffe, and G. R. Stewart. 1991. The role of glutamate dehydrogenase in plant nitrogen metabolism. Plant Physiol. 95: 509-516, 1991.
Rouquette, F. M., Jr. and V. A. Haby. 1996. Stand maintenance of ‘Alfagraze’ alfalfa seeded into bermudagrass and rotationally grazed. Agron. Abstracts 88:126.
Raun, W.R., G. V. Johnson, S. B. Phillips, W. E. Thomason, J. L. Dennis, and D. A. Cossey. 1999. Alfalfa yield response to nitrogen applied after each cutting. Soil Sci. Soc. Am. J. 65:1237-1243.
SAS Institute. 1994. SAS User's Guide: Statistics. Version 6 ed. SAS Institute, Inc., Cary, NC.
Smith, S.R.J., J. H. Bouton, and C.S. Hoveland. 1989. Alfalfa persistence and regrowth potential under continuous grazing. Agron. J. 81:960-965.
Soltanpour, P. N., G. W. Johnson, S. M. Workman, J. B. Jones, Jr., and R. O. Miller. 1996. Inductively coupled plasma emission spectrometry and inductively coupled plasma-mass spectrometry. p. 91-139 in Methods of Soil Analysis. Part 3. Chemical Methods – SSSA Book Series No. 5.
Srivastava, H.S. and R. P. Singh. 1987. Role and regulation of L-glutamate dehydrogenase in higher plants. Phytochemistry 26: 597-610.
Sorenson, E.L., R.A. Byers, and E.K. Horner. 1988. Breeding for insect resistance. In A. A. Hansen et al. (Eds.) Alfalfa and Alfalfa Improvement. American Soc. Agron., Madison, WI.
Subhan, D. and S. D. S Murthy. 2000. Synergistic effect of AlCl3 and kinetin on chlorophyll and protein contents and photochemical activities in detached wheat primary leaves during dark incubation. Photosynthetica 38: 211-214.
Sumner, M. E. 1993. Gypsum and Acid Soils: The World Scene. In: Sparks, D. L. (Ed.). Advances in Agronomy 51:1-32. Academic Press, Inc. San Diego, CA.
Sumner, M. E. 1995. Amelioration of subsoil acidity with minimum disturbance. In: Jayawardane, N. S. and B. A. Stewart (Eds.) Subsoil Management Techniques. Advances in Soil Science. Lewis Publishers. Boca Raton, FL.
Sumner, M. E., H. Shahandeh, J. Bouton, and J. Hammel. 1986. Amelioration of an acid soil profile through deep liming and surface application of gypsum. Soil Sci. Soc. Am. J. 50:1254-1258.
Tesar, M. B. and J. L. Yager, J.L. 1985. Fall cutting of alfalfa in the North Central USA. Agron. J. 77: 774-778.
Utley, P. R., H. D. Chapman, W. G. Monson, W. H. Marchant, and W. C. McCormick. 1974. Coastcross-1 bermudagrass, Coastal bermudagrass, and Pensacola bahiagrass as summer pasture for steers. J. Anim. Sci. 38:490-495.
Van Keuren, R. W. and A. G. Matches. 1988. Pasture production and utilization. p. 515-538. In A. A. Hanson, D. K. Barnes, and R. R. Hill, Jr. (ed). Alfalfa and alfalfa improvement. Agron. Monogr. 29. ASA, CSSA, and SSSA, Madison, WI.
Volenec, J.J., A. Ourry, and B.C. Joern. 1996. A role for nitrogen reserves in forage regrowth and stress tolerance. Physiol. Plant. 97:185-193.
Wilkinson, S.R., W.E. Adams, and W.A. Jackson. 1970. Chemical composition and in vitro digestibility of vertical layers of Coastal bermudagrass (Cynodon dactylon L.). Agron. J. 62:39-43.
Windholz, M. (Ed.) 1976. The Merck Index, 9th Ed., Merck & Co., Inc. Rahway, NJ. p. 216.
Yang, Y.H., and H. Y. Zhang. 1998. Boron amelioration of aluminum toxicity in mungbean seedlings. J. Plant Nutr. 21:1045-1054.
Yau, S.K. 2000. Soil-boron affects straw quality and other agronomic traits in two cultivars of barley. Commun. Soil Sci. Plant Anal. 31: 591-604.