Final Report for LS02-136
Project Information
Subproject 1: A pecan (Carya illinoensis Koch.) -cotton (Gossypium hirsutum L.) alley cropping system was established in northwestern Florida in Spring 2001 to assess the ecological, environmental and economic benefits of alley cropping. Polyethylene root barriers were used to prevent belowground interaction between pecan and cotton in half the number of test plots, for the entire length of the study (3 years). The study first examined the effect of light on cotton production and associated production physiology. We hypothesized that growth and productivity of cotton, a C3 plant, planted under “mature” pecan trees would not be affected adversely by shading if belowground competition for water and nutrients was eliminated. Results indicated that despite shading, the absence of belowground competition for resources in the barrier treatment increased radiation use efficiency by 30% over the non-barrier treatment. Aboveground biomass of cotton in the barrier treatment was similar to those of cotton in monoculture, but higher than those in the non-barrier treatment. The results suggested that competition for light was not a major factor driving productivity. In an attempt to quantify belowground competition for water, we examined soil water dynamics, leaf expansion and cotton and pecan water uptake. Results indicated that competition for water was a major determinant of productivity of cotton. Cotton leaf area, water uptake, biomass and lint yield were affected negatively by competition from pecan. We also examined competition for nitrogen in the system. First we quantified the effects of tree roots on nitrogen transformations in soil. It was observed that temporal variations in net ammonification, nitrification and mineralization were driven primarily by environmental factors (such as soil moisture content and soil temperature), and by initial ammonium and nitrate levels. In general, greater nitrification and mineralization rates were observed in the non-barrier treatment due to higher soil nitrogen. In addition, source of N was found to have a significant effect on cotton yield, with inorganic fertilizer resulting in higher yields in the barrier treatment compared with organic poultry litter. The results also indicated that competition for fertilizer N was minimal because of differences in temporal patterns of pecan and cotton nitrogen demand, although NDF may have occurred in unstudied portions of pecan tree tissue. Nitrogen use efficiency of cotton in barrier treatment was shown to be higher, indicating a greater ability to utilize the available nitrogen.The study also examined the “safety net” hypothesis to determine whether tree roots were able to capture nitrate and ammonium leached below the crop root zone. In general, the presence of trees in the non-barrier treatment resulted in decreased soil solution nitrate concentrations and nitrate leaching rates, thus providing proof for one of the major environmental benefits of alley cropping.
Subproject 2: This study was conducted on a 16-ha Pinus palustris-Paspalum notatum silvopasture at Ona, FL. Available forage averaged 2450 kg/ha in all pastures at the start in June, but forage availability declined steadily over the grazing period in silvopasture because pasture growth could not keep up with animal demand. In the open pasture, available forage increased from June to July, and then declined through September. Cows lost an average 88 kg on the silvopasture compared with a loss of 20 kg for open pasture over the 107-day period. Forage production needs to be enhanced either through reduction in pine density and/or intensive fertilization regimes to make silvopasture sustainable.
Subproject 3: This study estimated the profitability of pecan-cotton alley cropping under three scenarios: a) pure cotton and pecan production (PCPP); b) pecan-cotton alley cropping (PCAC); and C) pecan-cotton alley cropping with trenches (PCACT). The last scenario was to see the marginal impact of controlling tree-crop root interaction. The results suggested that the net present value (NPV) of pecan-cotton alley cropping with trenches (PCACT) is higher than those of pure cotton and pecan production (PCPP) and pecan-cotton alley cropping (PCAC). The NPV of PCAC was found to be greater than that of PCPP.
Overall, this project reveals that alley cropping or silvopasture can be managed as sustainable systems, but intensive management interventions are necessary. Environmental benefits such as reduction in nitrate leaching is realized in alley cropping and silvopastoral systems. They provide an alternative option to monocultural cropping systems on environmentally sensitive land. Economic analysis has revealed that agroforestry systems such as alley cropping can be economically viable, especially when negative component interactions are alleviated.
Subproject 1:
1. Quantify competition for light, water and nitrogen between pecan and cotton in an alley cropping system
2. Determine the degree to which nutrient uptake in trees affects groundwater ammoinum and nitrate levels in this system
Subproject 2:
1. Quantify forage production and cattle performance in a silvopasture vs. pasture system
Subproject 3:
1. Quantify the economic viability of alley cropping
Individuals and institutions in the world’s temperate regions are increasingly taking notice of the science and art of agroforestry systems. This is due in part to growing concerns over the long-term sustainability of intensive monocultural systems. Alley cropping and silvopasture are two agroforestry systems with great potential for adoption in the Southeast. In the temperate context, alley cropping involves the planting of timber, fruit or nut trees in single or multiple rows on agricultural lands, with crops or forages cultivated in the alleyways (Nair, 1993; Garrett and McGraw, 2000). Major purposes of this type of agroforestry system include production of tree or wood products along with crops or forage; improvement of crop or forage quality and quantity by enhancement of microclimatic conditions; improved utilization and recycling of soil nutrients for crop or forage use; control of subsurface water levels; and provision of favorable habitats for plant, insect or animal species beneficial to crops or forage (USDA, 1996; Garrett and McGraw, 2000). Important crops for alley cropping in the southern United States include cotton (Gossypium spp.), peanut (Arachis hypogaea), maize (Zea mays L.), soybean (Glycine max. L. (Merr.)), wheat (Triticum spp.) and oats (Avena spp.), combined with trees such as pines (Pinus spp.) and pecan (Carya illinoensis K. Koch).
Silvopasture systems involving pine and cattle have been in existence for decades; however, have received little attention. Recent studies have shown that silvopasture can be a profitable practice for small landowners. There are still unanswered questions regarding the optimum density of trees, forage quality and cattle performance.
As an association of plant and or animal communities, agroforestry systems are deliberately designed to optimize use of spatial, temporal and physical resources, by maximizing positive interactions (facilitation) and minimizing negative ones (competition) between trees/crops and animals (Jose et al., 2000a). For example, trees in these systems are capable of improving soil nutrient status (Nair, 1993; Palm, 1995; Rowe et al., 1999), thereby improving overall system productivity. Trees are also capable of capturing and recycling lost soil nutrients and are thus a potential moderating factor in groundwater pollution caused by leaching of nitrates (Williams et al., 1997; Garrett and McGraw, 2000). In addition, trees on agricultural lands offer landowners the possibility of accruing carbon credits via the sequestration of stable carbon stock, an added incentive for adopting alley cropping (Dixon, 1995; Williams et al., 1997; Sampson, 2001; Nair and Nair, 2003). However, adoption of alley cropping and other agroforestry systems has been hampered by a lack of understanding of interspecific interactions involving system components and their impact on system productivity and sustainability. This is especially true for temperate agroforestry systems, where research efforts have gained momentum only in recent years.
Research
Subproject 1: Study area and configuration:
This study was conducted at the West Florida Research and Education Center Farm of the University of Florida, located near Jay in northwestern Florida, USA (30°89’ N Lat., 87°13’ W Long.). The climate is temperate with mild winters and hot, humid summers. The soil at this site is classified as a Red Bay sandy loam, which is a fine-loamy, siliceous, thermic Rhodic Paleudult, and the average water table depth at the site is 1.8 m. For this study, a pecan-cotton alley cropping system was initiated in Spring 2001 from an existing orchard of pecan trees that had been planted at a uniform spacing of 18.28 m in 1954 and that had remained under grass cover until the current study. Ten plots were established within the orchard and arranged into five blocks using a randomized complete block design. Each plot, which consisted of two rows of trees oriented in an E/W direction, was 27.43 m long and 18.28 m wide, with a practical cultivatable width of 16.24 m, and was separated from its adjacent plot by a border area of the same dimensions. To assess tree root competition for nitrogen fertilizer, each block was randomly divided into a ‘barrier’ plot and a ‘no barrier’ plot. ‘Barrier’ plots were subjected to a root pruning treatment in the spring of 2001 in which a trenching machine was used to dig a 1.2 m deep trench along both sides of the plot at a distance of 1 m from the trees. A double layer of 6-mil polyethylene sheeting was then used to line the ditch, after which the trench was backfilled. ‘No barrier’ plots did not receive this root pruning treatment. The ‘barrier’ plots thus served as the no-competition treatment, while the ‘no barrier’ plots served as the tree-crop competition treatment.
Methods:
Objective 1:For this study, cotton (DP 458 B/RR) was planted in rows 0.96 m apart, at 16 rows per alley, in a N/S orientation, in 2001,2002 and 2003 following disking of the alleys. Conventional insecticide and herbicide were applied during the growing season as recommended. In each plot, one microplot (2.60 m x 0.76 m), containing 8-10 plants, was established on the first, fourth and eighth rows of cotton, respectively (going west to east in each plot). Light was measured at 30 minute intervals through the day once every two weeks from May through October. Photosynthesis, transpiration and stomatal conductance were measured on a monthly basis. Leaf area expansion was measured bi-weekly. To quantify nutrient competition, 15N enriched fertilizer ((NH4)2SO4, 5% atom enrichment) was uniformly hand-applied to microplots at a rate of 89.6 kg N ha-1, on 19 June 2001, at the same time, rate and formulation as the regular fertilizer application. Each microplot was arranged so that one of the pecan trees in the tree row was in the center and could serve as the target tree for 15N sampling (Figure 1). Six plants (aboveground portions) from each microplot were sampled for 15N content in leaf, stem and boll components. Cotton leaf samples were collected prior to leaf senescence. The same plants were harvested at physiological maturity, and separated into stem and boll components. In addition, foliar samples from each associated tree were collected. For this purpose, the tree canopy was divided into an upper and lower half, and leaves were collected via shotgun harvest method from all four cardinal directions in both the halves, to provide one composite sample per tree. Following collection, all plant tissue samples were air dried at 65°C for 72 hours. In preparation for combustion analysis, all green plant tissue samples (cotton leaves and stems, and tree leaves) were ground with a model 4 Wiley Mill to pass through a 1 mm screen, and then re-ground using a burr coffee grinder. All grinders were thoroughly cleaned between samples to prevent cross-contamination of the 15N plant material. Cotton lint was de-seeded and manually shredded in preparation for analysis. Soil cores, measuring 120 cm in length and 5 cm in diameter, were collected in pairs at random points within each microplot, using a tractor-mounted hydraulic corer and polyethylene collection tubes. The cores were divided into 30 cm increments to a depth of 120 cm, composited for each microplot depth, air dried, and a subsample was fine-ground with a mortar and pestle. For determination of total N and 15N concentrations, subsamples of the ground plant material and soil samples were analyzed by the University of Florida Geological Sciences Department (Gainesville, FL) using a Finnigan-MAT DELTAplus isotope ratio mass spectrometer with a ConFlo III interface attached to a Costech ECS 4010 elemental analyzer (Schepers et al., 1989). Percent nitrogen derived from fertilizer, percent utilization of fertilizer nitrogen, and percent nitrogen recovery in soil, were calculated from the enrichment data to determine the degree of interspecific competition for nitrogen.
Objective 2: Soil solution (free soil water that is not in equilibrium with the soil matrix) (Weston and Attiwill, 1996) was sampled 1-2 times monthly over a 15-month period from ceramic cup lysimeters installed in pairs at depths of 0.3 and 0.9 m at specific distances of 1.5, 4.2 and 8.4 m from a reference tree in each plot (Figure 1). Lysimeters were fitted with a highly porous (~45% porosity) ceramic cup (Soil Moisture Equipment Corp., Santa Barbara, CA) that allowed for collection of soil solution 24-48 hr after application of a vacuum (30-50 kPa) (Talsma et al., 1979). Samples were collected in 20 ml scintillation vials and kept frozen until analysis. Samples were analyzed for NH4-N and NO3-N concentrations by the Analytical Research Laboratory of the University of Florida (Gainesville, FL) using spectrophotometric analysis. Data for each month were averaged across rows to produce one observation per plot at each depth since initial analysis revealed no row effect (van Miegroet et al., 1994). In addition, a Hydrosense (Decagon Devices, Pullman, WA) water content reflectometry soil moisture probe was used on a monthly basis to determine volumetric water content within a 12 cm surface layer.
Subproject 2: Study area and configuration:
The study was conducted on a 16-ha Pinus palustris-Paspalum notatum silvopasture at Ona, FL. Trees were established in December 1991 in a ‘Pensacola’ P. notatum pasture at 1120 trees/ha where trees were planted in double-rows spaced 2.4 m apart, 1.2 m between pines within the row, and 12.2 m between double-rows. The silvopasture was sown to Desmodium heterocarpon in 1994 and Vigna parkeri in 2001. During the first 11 years of grazing, an average of 2 cow-calf pair/ha was maintained from March to October. By 2002, tree density was reduced to 494 trees/ha (44% of original planting density).
Methods:
During the summer of 2003 and 2004, when the trees were 12- and 13-years old, respectively, we grazed the silvopasture and compared forage and livestock production to a 8-ha open pasture (no pines) that contained a similar grass-legume mixture. In 2003, we used mature Braford cows and calves (112-day-old at start) in the silvopasture and open pasture stocked at 2.5 cow-calf pair/ha for 107 days from 1 June to 15 September 2003 when the calves were weaned. In 2004, we reduced stocking rates (based on 2003 results) to 2 cow-calf pair/ha in open pasture and 1.5 cow-calf pair/ha in silvopasture and grazed from 15 May to 30 September 2003.
Subproject 3: Study area and configuration (same as under subproject 1)
Methods:
This study estimated the profitability of pecan-cotton alley cropping under three scenarios: a) pure cotton and pecan production (PCPP); b) pecan-cotton alley cropping (PCAC); and C) pecan-cotton alley cropping with trenches (PCACT). The last scenario was to see the marginal impact of controlling tree-crop root interaction.
A partial budget model was used to estimate the profitability under these scenarios (Brown and Campbell 2004; Franzel 2004; Grado and Husak 2004). The data on inputs used and output produced under each scenario were compiled from both primary and secondary sources. The data on prices of inputs and outputs were obtained from local and published sources. The analyses were conducted for a period of 50 years, which corresponds to the life-span of a productive pecan tree. Decision criteria including net present values (NPV), benefit-cost ratio (BCR); and internal rate of return (IRR) were calculated for all three scenarios. In order to assess the sensitivity of decision criteria to the discount rate, the model was run under different discount rates. Societal values for environmental services such as carbon sequestration and wildlife habitat were compiled from the literature and used in the analysis to assess their effect on decision criteria.
Objective 1:
Our results indicate that cotton plants are subject to competition for nitrogen and perhaps water. Light was not a major determinant of productivity if belowground competition was alleviated. Competition for water resulted in significant reduction in cotton leaf area index and water uptake. It also resulted in significant reduction in net photosynthesis and transpiration. Competition for nitrogen was alleviated to a great extent by the application of fertilizer nitrogen. Further, nitrogen uptake and allocation patterns in both pecan and cotton were influenced largely by temporal difference in N demand and the abundance of mineralized nitrogen in soil. We observed increases in nitrogen content of cotton in the presence of root barrier, although the barrier had no significant effect on pecan leaf nitrogen concentration or canopy nitrogen content. NDF was lower for cotton in ‘barrier’ plants, indicating that cotton in this treatment was taking up a higher percentage of its nitrogen from nitrogen already present in the soil. However, NDF in pecan was minimal, indicating an early and substantial uptake of N prior to the cotton season and fertilizer application. Total UFN was higher in ‘barrier’ cotton plants, indicating a greater ability to utilize the available fertilizer efficiently. In soil, depth was the primary factor influencing nitrogen recovery, although a slight trend was observed at lower depths in the ‘no barrier’ treatment, where N levels were somewhat lower than levels in ‘barrier’ treatment. Apparently, fertilizer nitrogen was taken up by tree roots from these deeper horizons.
Objective 2:
The results of our study indicate that the competitive presence of trees can be utilized to decrease soil ammonium and nitrate concentrations and reduce N leaching in alley cropping systems. The “barrier” treatment had the potential to leach 23.79 kg N ha-1 yr-1 down below 0.9 m depth. The “no barrier” treatment exhibited a significantly lower potential for leaching with only 8.21 kg N ha-1 yr-1 below 0.9 m. For both treatments NO3-N accounted for 99.9% of the total inorganic nitrogen. These findings will improve our understanding of nitrogen dynamics in temperate alley cropping systems, which in turn, will help in designing systems that can utilize the ‘safety net’ role to maximize fertilizer use efficiency while minimizing groundwater nutrient-pollution.
Subproject 2:
In 2003, available forage averaged 2450 kg/ha in all pastures at the start in June, but forage availability declined steadily over the grazing period in silvopasture because pasture growth could not keep up with animal demand. In the open pasture, available forage increased from June to July, and then declined through September. Cows lost an average 88 kg on the silvopasture compared with a loss of 20 kg for open pasture over the 107-day period. Body condition scores of the cows in September were 4.9 and 3.8 in open pasture and silvopasture, respectively. Calf weights at weaning (236 days of age) were 212 kg on open pasture compared with 179 kg on silvopasture. Calf weaning weight on the 12-year old silvopasture was 15% lower, and cow weight loss was 4 times more than that on open pasture. These represented drastic reductions in livestock production compared with production when the trees were younger.
Available forage during the 2004 grazing period averaged 1750 kg/ha in silvopasture and 2130 kg/ha in open pasture. In both open pasture and silvopasture, available forage increased from May to July, and then declined through September. Cows lost an average 3 kg on the silvopasture compared with a gain of 49 kg on open pasture over the 143-day period (Table 1). Body condition scores of the cows in September were 5.7 and 4.3 in open pasture and silvopasture, respectively. Calf weight at weaning (255 days of age) was 266 kg on open pasture compared with 214 kg on silvopasture. Calves on open pasture gained an average of 136 vs. 84 kg on silvopasture. This is equivalent to 322 kg of gain/ha on open pasture vs. 123 kg/ha on silvopasture.
Subproject 3:
The results suggested that the NPV of pecan-cotton alley cropping with trenches (PCACT) is higher than those of pure cotton and pecan production (PCPP) and pecan-cotton alley cropping (PCAC). The NPV of PCAC was found to be greater than that of PCPP. Results also indicated that the NPV of both PCACT and PCAC would be much higher than that of PCPP when societal values for carbon sequestration and wildlife habitat are incorporated into the analysis. An increase in the discount rate was found to decrease the NPV of all scenarios. Several conclusions and management implications were drawn from these results. First, farmers would be better-off, in terms of profitability, to switch from pure cotton and pecan production to some sort of alley cropping. Second, it would be beneficial for farmers to control the tree-crop root interaction, within alley cropping system, through small trenches or deep discing. Third, societal values for environmental services associated with alley cropping, if internalized, might stimulate more farmers to switch from pure cropping to alley cropping. In order to internalize these environmental services, however, appropriate institutions and government commitment are required.
This study can be extended in several different ways. First, a dynamic optimization procedure can be applied to estimate the land value and annual rent under three different scenarios (Stainback and Alavalapati 2004). Second, we conducted the analysis based on the inputs and outputs of one study site. Therefore, the results may not be applicable for a wider region. Data from more study sites would provide more robust estimates. Third, societal values for environmental services used in the analysis are drawn from secondary sources. It would be useful to obtain that data from contingent valuation surveys and incorporate into the analysis.
Educational & Outreach Activities
Participation Summary:
Book Chapters
1. Nair, P.K.R., Bannister, M.E., Nair, V.D., Alavalapati, J.R.R., Ellis, E., Jose, S., and Long A.J. 2005. Silvopasture in southeastern United States: More than just a new name for an old practice. Mosquera-Losada, M.R., McAdam, J., and Riguero-Rodriguez, A. (eds.), CABI Publishing, Wallingford, U.K. (invited).
2. Zamora D., Jose, S., Nair, P.K.R. 2005. Competition for light in a pecan-cotton alley cropping system. Ecological Interactions in Agroforestry. Jose, S,. and Gordon, A, (eds.). Springer, New York (in press)
3. Jose, S., Gillespie, A.R., and Pallardy S.G. Interspecific interactions in temperate agroforestry. In New Vistas in Agroforestry. Nair, P.K.R., Rao. M.R., and Buck, L.E. (ed.), Kulwer Academic Publishers, Dordrecht, The Netherlands. In press (invited).
3. Jose S., Allen S.*, and Nair P.K.R. 2004. Ecological interactions: Lessons from temperate alley cropping systems. In Agroforestry. Batish S. and Singh H.P. (eds). Haworth Press, New York. In press (invited)
Refereed Journal Articles:
1.Allen, S.*, Jose, S., Nair, P.K.R., Brecke, B.J., Nair, V.D., Graetz, D. and Ramsey, C.L. 2005. Nitrogen mineralization in a pecan (Carya illinoensis K. Koch)-cotton (Gossypium hirsutum L.) alley cropping system in the southern United States. Biology and Fertility of Soil 41: 28-37
2. Allen, S.*, Jose, S., Nair, P.K.R., and Brecke, B.J. 2004. Competition for 15N labeled nitrogen in a pecan-cotton alley cropping system in the southern United States. Plant and Soil 263: 151-164
3. Allen, S.*, Jose, S., Nair, P.K.R., Brecke, B.J., Nkedi-Kizza, P. 2004. Safety net role of tree roots: Experimental evidence from an alley cropping system. Forest Ecology and Management 192:395-407 [Media Coverage: Press Release by University of Florida on August 11, 2004; News and interviews appeared in several newspapers (e.g.; The Okeechobee News, Southeast Farm Press) and science magazines (e.g. SeedQuest) in FL and elsewhere]
4. Wanvestraut, R.*, Jose, S., Nair, P.K.R., and Brecke, B.J. 2004. Competition for water in a pecan-cotton alley cropping system in the southern United States. Agroforestry Systems 60:167-179.
5. Jose, S., Gillespie, A.R., and Pallardy S.G. 2004. Interspecific interactions in temperate agroforestry. Agroforestry Systems 61:237-255.
6. Lee, K.H.* and Jose, S. 2003. Soil respiration and microbial biomass in a pecan-cotton alley cropping system in southern USA. Agroforestry Systems 58:45-54.
Dissertation:
Zamora, D. 2005. Competitive Interactions Involving Light in a Pecan-cotton alley cropping system. Ph.D. dissertation, University of Florida, Gainesville, FL.
Allen, S. 2003. Nitrogen dynamics in a pecan-cotton alley cropping system. Ph.D. dissertation, University of Florida, Gainesville, FL.Conference
Theses:
Wanvesatraut R. 2003. Competition for water in a pecan-coptton alley cropping system in the southern United States. M.S. Thesis, University of Florida, Gainesville, FL.
Napolitano, K. 2005. Porduction dynamics in a loblolly pine-cotton alley cropping system (in progress)
Conference Presentations:
1. Jose, S. 2004. Interspecific interactions: Principles and applications in forestry and agroforestry. Department of Renewable Resources Seminar, University of Alberta, Edmonton, October 5, Alberta, Canada. (Invited).
2. Nair, P.K.R., Bannister, M.E., Nair, V.D., Alavalapati, J.R.R., Ellis, E., Jose, S., and Long A.J. 2004. Silvopasture in southeastern United States: More than just a new name for an old practice. International Congress on Silvopastoralism and Sustainable Management. April 18-24. Lugo, Spain (Keynote speech given by P.K. Nair)
3. Nair, V.D., Jose, S., Kalmbacher, R.S., Graetz, D.A., and Nair P.K.R. 2004. Reducing nutrient loss from Florida soils through agroforestry practices. 1st World Congress of Agroforestry. June 27-July 2. Orlando, FL (moderator at this conference)
4.Zamora, D., and Jose, S. 2004. Root morphological plasticity in Gossypium hirsuitum in response to competition. 1st World Congress of Agroforestry. June 27-July 2. Orlando, FL
5. Zamora, D., Jose, S., and Nair P.K.R. 2004. Light distribution and radiation use efficiency of a pecan-cotton alley cropping system in southern U.S.A. 1st World Congress of Agroforestry. June 27-July 2. Orlando, FL
6. Ramsey, C., and Jose, S. 2004. Water use efficiency of Gossypium hirsuitum in response to competition in a temperate alley cropping system. 1st World Congress of Agroforestry. June 27-July 2. Orlando, FL
7.Jose, S. 2003. Tree-crop interactions in temperate alley cropping: Ecological principles and evaluation techniques. Ecology Seminar Series, School of Environmental Science and Management, Southern Cross University, October 3, Lismore, NSW, Australia (invited).
8.Allen, S.C.*, Jose, S., Nair, P.K.R., Nair, V.D., Graetz, D. 2003. Competition for nitrogen in a temperate alley cropping system with pecan and cotton. Eight North American Agroforestry Conference, June 22-25, Corvallis, Oregon.
9.Allen, S.*, Jose, S., Nair, P.K.R., Nair, V.D., Graetz, D., and Ramsey, C.L. 2003. Nitrogen mineralization in a temperate alley cropping system in the southern United States. ASA-CSSA-SSSA Annual Meeting, November 2-6, Denver, CO.
10.Allen, S.*, Jose, S., Nair, P.K.R., Brecke, B.J, and Ramsey, C.L. 2003. Experimental evidence for the safety-net hypothesis from a temperate alley cropping system. ASA-CSSA-SSSA Annual Meeting, November 2-6, Denver, CO.
Extension Publication/Outreach1.
Workman S., Allen, S.C.*, Jose, S. 2003. Alley cropping combinations for the southeastern U.S. Florida Cooperative Extension Service Fact Sheet, FOR 106. 6p. UF/IFAS EDIS Database, http://edis.ifas.ufl.edu/BODY_FR142
Project Outcomes
Outcome from the agroforestry project will be used to provide a profile of the component interactions and their influence on system productivity in temperate agroforestry systems. This knowledge will help to improve our basic understanding of temperate agroforestry systems, so that better systems can be created, with tighter nutrient cycling and reduced groundwater pollution.
Ultimately, it is hoped that this research will encourage farmers and landowners to adopt agroforestry practices. The researchers believe that such systems can help to diversify and strengthen the family farm, by providing alternate forms of income at various times of the year, while utilizing land that would otherwise remain unused. The prospect of reducing nitrate levels in groundwater is also an exciting possibility for these types of systems, which is a vision that we hope landowners are able to catch.
Economic Analysis
Although the economic analysis is outlined under subproject 3, it is repeated here. This study estimated the profitability of pecan-cotton alley cropping under three scenarios: a) pure cotton and pecan production (PCPP); b) pecan-cotton alley cropping (PCAC); and C) pecan-cotton alley cropping with trenches (PCACT). The last scenario was to see the marginal impact of controlling tree-crop root interaction.
A partial budget model was used to estimate the profitability under these scenarios (Brown and Campbell 2004; Franzel 2004; Grado and Husak 2004). The data on inputs used and output produced under each scenario were compiled from both primary and secondary sources. The data on prices of inputs and outputs were obtained from local and published sources. The analyses were conducted for a period of 50 years, which corresponds to the life-span of a productive pecan tree. Decision criteria including net present values (NPV), benefit-cost ratio (BCR); and internal rate of return (IRR) were calculated for all three scenarios. In order to assess the sensitivity of decision criteria to the discount rate, the model was run under different discount rates. Societal values for environmental services such as carbon sequestration and wildlife habitat were compiled from the literature and used in the analysis to assess their effect on decision criteria.
The results suggested that the NPV of pecan-cotton alley cropping with trenches (PCACT) is higher than those of pure cotton and pecan production (PCPP) and pecan-cotton alley cropping (PCAC). The NPV of PCAC was found to be greater than that of PCPP. Results also indicated that the NPV of both PCACT and PCAC would be much higher than that of PCPP when societal values for carbon sequestration and wildlife habitat are incorporated into the analysis. An increase in the discount rate was found to decrease the NPV of all scenarios. Several conclusions and management implications were drawn from these results. First, farmers would be better-off, in terms of profitability, to switch from pure cotton and pecan production to some sort of alley cropping. Second, it would be beneficial for farmers to control the tree-crop root interaction, within alley cropping system, through small trenches or deep discing. Third, societal values for environmental services associated with alley cropping, if internalized, might stimulate more farmers to switch from pure cropping to alley cropping. In order to internalize these environmental services, however, appropriate institutions and government commitment are required.
This study can be extended in several different ways. First, a dynamic optimization procedure can be applied to estimate the land value and annual rent under three different scenarios (Stainback and Alavalapati 2004). Second, we conducted the analysis based on the inputs and outputs of one study site. Therefore, the results may not be applicable for a wider region. Data from more study sites would provide more robust estimates. Third, societal values for environmental services used in the analysis are drawn from secondary sources. It would be useful to obtain that data from contingent valuation surveys and incorporate into the analysis.
Areas needing additional study
1. Incorporate information from above and belowground interaction studies into a process level agroforestry model so that production dynamics can be predicted for a suite of species and management practices
2. Investigate the "safety-net" role of tree roots in younger agroforestry systems.