- Agronomic: cotton
- Nuts: pecans
- Additional Plants: trees
- Animals: bovine
- Animal Production: feed/forage
- Crop Production: agroforestry, alley cropping, fertilizers, silvopasture
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.
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
1. Quantify forage production and cattle performance in a silvopasture vs. pasture system
1. Quantify the economic viability of alley cropping