Three experiments were established to evaluate incorporating rhizoma peanut (RP) into low-input pasture systems in Florida. An establishment study illustrated that Florigraze and Ecoturf RP have the greatest potential for incorporation into strip-planted bahiagrass systems. Evaluation of new RP genotypes indicates that while total herbage accumulation was not affected by grazing management in Year 1, changes in above and below-ground sward characteristics suggest that RP genotypes may favor a 6- vs. a 3-wk regrowth interval. In the forage systems study, the greater productivity of bermudagrass compared with RP and use of grazing vs. hay harvest increased plant litter pools and the potential for C and N contribution.
The purpose of this project is to develop strategies that facilitate legume incorporation into grass-based livestock production systems in the USA Gulf Coast Region and to quantify the effect of this practice on soil quality. This technology is needed because current production systems are based on nitrogen (N)-fertilized grasses and are increasingly vulnerable to high fertilizer cost.
In the USA Gulf Coast Region, warm-season perennial grasses such as bahiagrass (Paspalum notatum Flügge) and bermudagrass [Cynodon dactylon (L.) Pers.] form the basis for grazing systems (Ball et al., 2007). Fluctuating costs of inputs to these systems, especially fuel and fertilizer, have made incorporation of legumes increasingly necessary for pasture-based livestock production. Legumes are high in nutritive value and fix N2, decreasing the need for commercial N fertilizer, an input that has become too expensive for some producers. Rhizoma peanut (RP; Arachis glabrata Benth.) is a warm-season perennial legume that is well adapted to the region and has potential for incorporation into grazing systems. Unlike most warm-climate legumes, RP has well-documented persistence and ability to spread in grass pastures (Ortega-S. et al., 1992). Some existing pastures have persisted for 30 years (L.E. Sollenberger, personal communication, 2011).
High cost of establishment of pure stands of RP (~ $550/acre) has made it uneconomical for use in livestock enterprises with relatively low return, e.g., beef cow-calf systems, and limited its use primarily to a high value hay crop for horses or dairy cattle. Lower-cost, alternative establishment strategies are needed if RP is to make significant contributions to grazing systems for livestock. One approach for lower-cost incorporation of RP into grass pastures is strip-planting. Because RP is a long-lived perennial with ability to move laterally via an extensive rhizome system, it has potential to spread into the surrounding grass areas over time and form a mixed pasture. Recently-released cultivars of RP range in growth habit from decumbent to upright, and these differences likely will affect their ability to spread in grass pastures (Quesenberry et al., 2010). Plants with varying growth habits also will likely respond differently to a range of grazing management strategies. No research has evaluated responses of RP cultivars with varying growth habits to strip-planting or to grazing management. The success of the strip-planting approach is dependent upon selecting RP cultivars that spread vigorously in grass pastures and tolerate grazing. The proposed research is designed to identify these cultivars.
Finally, increasing emphasis is being placed on the ability of grasslands to provide ecosystem services, and conversion to RP-based systems has potential to contribute significantly (French et al., 2006). Tropical and temperate grasslands play a major role in the global C cycle and serve as an important C sink. Management of grass-based forage systems, e.g., N fertilization, haying vs. grazing, and grazing at a range of stocking rates, affects their potential to store C (Franzluebbers and Stuedemann, 2009), but little attention has been given to perennial legume-based pasture systems. This information is needed, and the proposed research will be an important step toward providing it.
- To quantify the effects of growth habit of rhizoma peanut (RP) and defoliation management during the establishment year on ground cover and rate of spread of RP cultivars following strip planting into bahiagrass pasture
- To measure the effect of grazing intensity and frequency on forage accumulation, persistence, and nutritive value of four RP cultivars differing in plant growth habit
- To quantify the effect on soil organic carbon and nitrogen accumulation of forage systems based on RP or nitrogen-fertilized bermudagrass
Objective 1: Rhizoma peanut cultivars (UF Peace, Ecoturf, Florigraze, and Arblick) were strip-planted in bahiagrass sods in 2011 and 2012 at the University of Florida Beef Research Unit. A critical question for producers is whether and how the undisturbed grass strips can be utilized during peanut establishment. Thus, treatments include all factorial combinations of two levels of defoliation management during the establishment year (main plots) and four RP cultivars (subplots). The eight treatments were replicated three times in a split-plot arrangement of a randomized complete block design. Two defoliation treatments were selected based on preliminary data from a previous strip-planting study with Florigraze RP (Castillo et al., 2013) which showed that continuous stocking is not a viable option. Defoliation treatments were imposed starting ~ 10 wk after planting (when sprout emergence was complete) and included:
1.) Hay production management – plot area harvested mechanically every 28 d to a 10-cm stubble height.
2.) Rotational stocking management – plot area grazed every 28 d to a 15-cm bahiagrass stubble height (preliminary research showed that cattle graze peanut strips preferentially, thus the taller height for grazed than clipped bahiagrass)
Sprout emergence was determined weekly after first-sprout emergence was observed (starting ~3 wk after planting) until 10 wk after emergence by counting the number of sprouts within four, 20- by 50-cm quadrats per plot.
Percent RP ground cover was estimated visually every 28 d. A 0.5- × 2-m quadrat was placed in the center of the RP strip at two marked locations along the length of the strip so that ground cover was estimated each time from the same area. The quadrat was divided into 100, 10- by 10-cm squares to facilitate estimations. Percent ground cover was estimated visually in twenty of the squares and averaged across squares and quadrats.
Frequency of RP occurrence in the planted strip was calculated as the proportion of total quadrats sampled within an experimental unit in which RP is present. Measurements were taken every 28 d. Presence of RP was determined in twenty stratified 10- by 10-cm squares per quadrat placement (total of 40 per plot). Frequency was calculated as: Frequency (%) = [# of quadrats where RP is present/40] × 100.
Finally, RP spread was measured at four locations per plot as the distance from the center of the planted strip (a transect) to edges where distinguishable RP plant parts were found (along lines perpendicular to the transect).
Objective 2: A 2-yr experiment was conducted at the University of Florida Beef Research Unit to assess the performance under grazing of established stands of three new and one industry standard RP cultivar. The experiment included 16 treatments, consisting of the factorial combinations of four RP cultivars and four grazing management regimes, arranged in two replicates of a randomized complete block design. Plot size is 9-m2. Treatments included:
1) Rhizoma peanut cultivar (growth habit)
- Florigraze (intermediate)
- UF Peace (upright)
- UF Tito (upright)
- Ecoturf (decumbent)
2) Defoliation management
- Grazing frequency – 3- and 6-wk intervals
- Grazing intensity– 50 and 75% removal of pregraze herbage (based on canopy height, not mass; widely varying growth habits preclude use of a standard postgraze stubble height)
Herbage mass was measured using a calibrated rising plate meter before and after each grazing event. Herbage accumulation was measured as the change in herbage mass between sampling after a grazing event and immediately prior to the next event. Crude protein and in vitro digestion were determined from samples taken to represent animal diets. Pregraze herbage mass samples were separated to determine percentage of RP, grass, and weeds at the beginning and end of each grazing season as an indicator of RP persistence. Other measures of persistence included percent cover of peanut, weed frequency, and rhizome total non-structural carbohydrate reserves. To assess the effect of grazing treatment on regrowth and regrowth potential, light interception was measured before, and residual leaf area after, a grazing event.
Objective 3: Five forage systems based on either FlorigrazeRP or Tifton 85 bermudagrass were established in 2011, and management effects on soil organic carbon and total soil N were evaluated in 2012 and 2013. Treatments were replicated three times in a split-plot arrangement of a randomized complete block design. Perennial forage species (RP or bermudagrass) were considered the main plot. Within each main plot there were five production systems for a total of 10 treatments. The systems evaluated included:
- Hay production of the warm-season (WS) forage; no overseeded cool-season (CS) forage
- Hay production of the WS forage during summer and of overseeded rye during winter
- Grazing of the WS forage during summer; no overseeded CS forage
- Grazing of the WS forage during summer and of overseeded rye during winter
- Hay production of the WS forage during summer followed by grazing of overseeded rye during winter
Soil cores were taken prior to treatments being imposed and at the end of the second experimental year to a depth of 100 cm using a Giddings soil probe, and the soil profile sampled in layers including 0 to 10, 10 to 20, 20 to 40, 40 to 70, and 70 to 100 cm. Samples from layers were dried at 55º C and bulk density determined. Total organic C and total N of each soil layer was determined by dry combustion using a Carlo Erba NA-1500 C/N/S analyzer. Soil samples were collected to a depth of 20-cm and separated into 0 to 10 and 10 to 20 cm layers at the end of one year of management. Because changes in soil C occur slowly and this was a relatively short study period, soil organic matter of surface soil layers (0 to 10 cm and 10 to 20 cm) will be fractionated by particle size and analyzed for C and N (Six et al., 2000; Dubeux et al., 2006). These analyses provided an early indication of changes due to treatment.
A 2-yr establishment study (2011 and 2012) was conducted at the UF/IFAS Beef Research Unit in Gainesville, FL to quantify establishment success, spread, and grazing tolerance of RP genotypes within the context of strip planting. Total sprout emergence (# sprouts m-2) was measured weekly beginning 3 wk after planting until defoliation was initiated on 15 June 2011 and 14 June 2012, respectively. Percentage of RP cover and frequency of occurrence were measured prior to each defoliation event. Spread was measured at the end of the season in October of each year. Total sprout emergence was greatest for Florigraze compared with all other entries (79 sprouts m-2). Percentage cover and frequency of Florigraze (26% cover and 59% freq) and Ecoturf (25% cover and 59% freq) was greater than Peace (11% cover and 34% freq), but was not different from Arblick (19% cover and 47% freq). Although defoliation management of RP did not affect cover and frequency as much as did RP genotype, spread potential was reduced by grazing (0 m) compared with haying (0.24 m) treatments. Results of this experiment suggest that selection of RP and management during the establishment year affect the rate and success of establishment of RP–grass associations in the southeastern USA. When strip-planted, Florigraze and Ecoturf RP had favorable sprout emergence, ground cover, frequency, and spread during the year of planting compared with Arblick and Peace RP. Rotational stocking of establishing pastures every 28 d decreased establishment success compared with a hay production system.
Recently released genotypes of rhizoma peanut (Arachis glabrata; RP) represent a range of growth habits which may affect their persistence under grazing. Their response to grazing, however, has not yet been evaluated and optimal management practices have not been defined. The objective of this study was to quantify sward canopy responses to grazing frequency and intensity in order to assess relative grazing tolerance among RP genotypes. Treatments were the factorial combinations of four RP genotypes [Florigraze, UF Peace, UF Tito, and Ecoturf], two grazing intensities (50 and 75% canopy removal), and two grazing frequencies (3 or 6 wk), arranged in two replications of a randomized complete block design. Herbage accumulation (HA) was estimated throughout the grazing season from June to October 2012. Greater HA was associated with the 6-wk grazing frequency compared to the 3-wk frequency (6,630 vs. 5,290 kg ha-1, respectively). Percentage RP ground cover and weed frequency were measured at the beginning and end of the grazing season in June and October 2012. Mean ground cover across the season was greater for Ecoturf (95%) compared with all other genotypes, and less weed frequency was associated with the 6-wk than 3-wk grazing frequency (34% vs. 45%, respectively). Pregraze light interception (LI) and leaf-to-stem ratio, and postgraze residual leaf area index (RLAI) were quantified during July and August 2012. Grazing frequency affected LI, with the 6-wk treatment having greater LI (91%) compared with the 3-wk interval (85.0%). A genotype effect was observed for postgraze RLAI where Ecoturf had greater RLAI than Florigraze and UF Tito (1.2 vs. 0.81 and 1.05, respectively). UF Peace was not different from Ecoturf and UF Tito, but had greater RLAI (1.19) than Florigraze. Residual leaf area was less for 75 than 50% canopy removal (0.89 vs. 1.23, respectively). Pregraze leaf-to-stem ratio was greater for Ecoturf (1.75) compared with UF Peace, Florigraze, and UF Tito (1.34, 1.47, 1.44, respectively). The 3-wk grazing frequency resulted in lesser leaf-to-stem ratio compared to the 6-wk frequency (1.41 and 1.59, respectively). These data suggest that the prostrate growth habit of Ecoturf is associated with greater ground cover and leaf-to-stem ratio before grazing and RLAI following defoliation events. Greater pregraze LI with the 6- vs. 3-wk grazing frequency and greater RLAI with 50 vs. 75% removal suggest that these levels of the treatment factors likely favor RP persistence and these data are supported by observational data collected in Year 2. A second year of this study was conducted from June to October 2013. Results from Year 2 are being summarized for publication.
Lastly, RP was used as the base forage in various production systems to determine its effect on herbage and soil quality compared with a grass-nitrogen system. Bermudagrass-based systems had greater herbage harvested and litter mass deposition than management systems associated with RP following one year of management. However, the litter C:N ratio of RP suggested a greater potential for mineralization than BG. Overseeding RP and BG with an early-maturing rye in this study did not negatively impact production of the warm-season perennials, indicating its utility as a winter forage option for producers in Florida, although total herbage harvested was lower than presented in the regional literature (Day et al., 2013). Following 1 yr of imposing management treatments on the year-round forage systems (summer and winter haying vs. grazing), soil C had increased in the macroaggregate (2000-250 µm) fraction, which best reflects short-term contributions of organic matter inputs from the systems. These data are supported by a decrease in the mass of ≤ 53 µm aggregate size fraction (silt + clay sized particles; g kg-1 total soil) from planting in 2011 to the end of the 2012 management season. A second year of data was collected during the 2013 winter and summer management season. Plant and soil data are currently being analyzed and will form the basis for a forage and soil management publication, respectively.
Educational & Outreach Activities
These projects formed the basis for the dissertation research of Kim Mullenix that was completed and defended in October 2013.
Mullenix, M. K. 2013. Strategies for increasing rhizoma peanut contribution to productivity and ecosystem services of low input pasture systems. Ph.D. Dissertation. University of Florida, Gainesville, FL.
- Peer-Reviewed Journal Articles in Development
Mullenix, M. K., L. E. Sollenberger, A. R. Blount, J. M. B. Vendramini, M. L. Silveira, and M. S. Castillo. 2014. Growth habit of rhizoma peanut affects establishment and spread when strip-planted in bahiagrass pastures. Crop Sci. (in review).
Three additional publications are expected from the work of this proposal. The second year of data for the RP grazing trial and the ecosystem services study are being summarized by Kim Mullenix and incorporated into the framework of the chapters from the dissertation. It is anticipated that one forage management paper will emerge from the rhizoma peanut cultivar grazing evaluation trial, and two papers from the management systems study.
Sollenberger, L. E., A. R. Blount, J. M. B. Vendramini, K. H. Quesenberry, M. S. Castillo, M. K. Mullenix, and M. O. Wallau. 2013. UF Beef Cattle Short Course: Agronomy Forage Research Update.
Mullenix, M. K., L. E. Sollenberger, A. R. Blount, M. S. Castillo, J. M. B. Vendramini, and M. L. Silveira. 2013. Growth habit of rhizoma peanut cultivars affects establishment and spread when strip-planted in bahiagrass sods. Proceedings of the American Forage and Grassland Council Meeting. Jan. 6-9, 2013. Covington, KY.
When planted in strips, Florigraze and Ecoturf generally had the greatest mean cover and frequency of occurrence throughout the study. Ground cover differences due to defoliation regime were more apparent during the year after establishment and early in the third year, with grazed plots having less RP cover compared with those under hay production. Spread of RP entries was reduced under grazing every 28 d compared with the hay production treatment during the establishment year, but differences were less pronounced in the year after establishment. Greater rhizome-root mass was associated with entries with greater above-ground cover and may play a role in rate of RP establishment. These results indicate that differences exist among commercially available RP entries in their ability to establish in strip-planted swards, with these results favoring Ecoturf and Florigraze. Selection of defoliation management strategy is an important consideration that can impact the success of RP establishment during the year of planting and in subsequent growing seasons. Hay production following strip-planting is a more favorable option for utilizing the grass component during the establishment phase while reducing removal of RP in the planted strip.
Grazing management strategies were observed to impact sward characteristics of RP genotypes during Year 1 of the RP grazing study. Although there were no differences among grazing treatments for total HA in Year 1, similar or greater leaf-to-stem ratio and pre-grazing light interception, and maintenance of a high percentage of ground cover with the 6-wk frequency suggest an advantage for longer regrowth intervals. Greater RLAI, less WF, and trends for greater pre-grazing sward height associated with the 50 vs. 75% removal level may favor RP persistence. Increased cover for the 3-wk frequency at the end of Year 1 may be associated with canopy structural adaptation of RP genotypes under short regrowth cycles. A second year of evaluation was conducted through summer 2013 to quantify continuing changes in sward canopy characteristics of entries under these strategies and data is currently being analyzed. The results indicate that while total HA was not affected by grazing management strategy in Year 1, changes in other above and below-ground sward characteristics suggest that RP genotypes may favor a 6- vs. a 3-wk regrowth interval and that these differences may become more pronounced over time. Selection of RP genotypes that exhibit grazing tolerance through increased production, persistence, and nutritive value will likely increase the use of these entries in pastures by producers.
Year-round forage production system affected the amount of herbage harvested and contribution of herbage to residual plant litter following one year of management. The greater inherent productivity of BG compared with RP and use of grazing vs. hay harvest increased plant litter pools and the potential for C and N contribution. The greater C:N ratio of plant residue from RP-based systems favored mineralization over that from BG systems, which may more readily impact short-term soil C and N pools. Overseeding RP and BG with an early-maturing rye did not influence subsequent herbage production of the warm-season perennials during Year 1 of the study. Interseeding cool-season annuals into these systems may provide an additional winter forage option for producers when planting in clean-tilled soils is not an option. Although there was a decrease in soil C for the < 53 μm fraction, the increase or maintenance of C in larger soil fractions illustrates newly added organic material in the soil, and suggests that production systems used in the present study were contributing to the accumulation of soil C and N. Greater C accumulation in the > 250 µm fraction for the summer-winter grazing management system compared with year-round hay production illustrates the short-term contribution of nutrient return from plant litter and excreta from livestock.
Scientific and Extension-Related Presentations (All Given by M. K. Mullenix)
Mullenix, M. K., L. E. Sollenberger, A. R. Blount, M. O. Wallau, J. M. B. Vendramini, M. L. Silveira. 2013. Effects of grazing management strategies on sward responses of rhizoma peanut genotypes. ASA-CSSA-SSSA International Annual Meeting. Nov. 3-6, 2013. Tampa, FL.
Mullenix, M. K., L. E. Sollenberger, A. R. Blount, M.S. Castillo, J.M.B. Vendramini, and M. L. Silveira. 2013. Establishment and spread of rhizoma peanut genotypes strip-planted in bahiagrass swards. ASA-CSSA-SSSA International Annual Meeting. Nov. 3-6, 2013. Tampa, FL.
Mullenix, M. K., M. Castillo, and L. E. Sollenberger. 2013. Improving warm-season pastures with perennial peanut. Georgia Cattlemen’s Convention. April 4, 2013. Perry, GA.
Mullenix, M. K., L. E. Sollenberger, D. L. Rowland, J. M. B. Vendramini, A. R. Blount, M. L. Silveira, A. Vaccarro. 2013. Sward responses of rhizoma peanut cultivars under a range of grazing management strategies. ASAS Southern Section Meeting, Feb 4, 2013. Orlando, FL.
Mullenix, M. K., L. E. Sollenberger, A. R. Blount, M. Castillo, J. M. B. Vendramini, and M. L. Silveira. 2012. Growth habit of rhizoma peanut cultivars affects establishment and spread when strip-planted in bahiagrass sods.ASA-CSSA-SSSA Annual Meeting. Oct 20-24, 2012. Cincinnati, OH.
Mullenix, M. K. 2012. Growth habit of perennial peanut affects spread into bahiagrass sod. 12th Annual Perennial Peanut Producer’s Association Field Day. Gainesville, FL.
Scientific and Extension-Related Presentations (Given by Co-Investigators)
Sollenberger, L.E., M. S. Castillo, and M. K. Mullenix. Establishment and grazing management of perennial peanut. 13th Annual Perennial Peanut Producer’s Association Field Day. Quincy, FL. June 2013.
Sollenberger, L.E., M.K. Mullenix, M.S. Castillo, and M.O. Wallau. UF-Agronomy forage research update. Florida Forage Workers Tour. Citra, FL. August 2013.
Data from the RP experiments at the Beef Research Unit were a key focus of a producer-based Perennial Peanut Field Day in Gainesville, FL in July 2012 and one held in Quincy, FL in June 2013. In Gainesville, seventy-five attendees viewed the experiments that were designed to provide systems recommendations for management of RP in pastures. A post workshop evaluation suggested that 97% of the surveyed population planned to utilize the information presented during the field day. One hundred and thirty participants heard presentations of the results of these experiments at the 2013 Perennial Peanut Field Day. A request was made at that time for producers interested in using the technology to contact the investigators. This lead the cooperators in the current project to develop a SARE on-farm research grant proposal in late 2013. This grant was awarded and on-farm work evaluating technologies developed in these experiments will be initiated on four farms starting in 2014.
Areas needing additional study
Identification of alternative grazing management strategies are needed if RP entries are to be grazed during the establishment phase without negatively impacting stand establishment. Evaluation of strip-planting into warm-season perennial grass pastures other than bahiagrass would provide needed information to beef cattle producers considering the adoption of this technology. Identifying complementary growth habits of both the grass and legume component in these systems will likely be needed to achieve successful stand establishment.
A third year of the RP grazing study may illustrate more long-term impacts of grazing management strategies on stand persistence. Hernández-Garay et al. (2004) showed that the percentage of Arbrook and Florigraze RP in pasture herbage mass was similar under 2 yr of continuous stocking ; however, the percentage of Arbrook decreased during year 3 of the study (89 to 66% from Year 1 to Year 3). This study suggests that RP responses to grazing management may become more prevalent over time, and subsequent years of management may more clearly illustrate grazing tolerance of new cultivars.
Continuing evaluation of forage management practices is necessary to determine the long-term effects of grazing and hay production on soil quality and the capacity of Florida soils to retain C within different particle size classes. The soil-focused study initiated under this grant is being continued for at least three additional years to assess longer-term impact of the management treatments on soil C dynamics.