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Environmental Benefits of Agroforestry Systems, Soil Conservation Project Team D.A. Shannon, K. H. Yoo, Auburn University,
Auburn, AL Rationale/Objectives Alley cropping with hedgerows of closely planted trees has been promoted for soil and water conservation in many parts of the tropics. This agroforestry practice is being tested as an alternative to conventional underground pipe-outlet terraces for soil and water conservation in the southeastern U.S. Assessment is based on crop yield, nutrient uptake in maize, surface water runoff, sediment and nutrient losses from plots and cost-benefit analysis. Work Done
Alabama. Three alley cropping treatments with hedgerows of mimosa (Albizia julibrissin), blackberry (Rubus ursinus) and switchgrass (Panicum virgatum), are compared to conventional underground pipe-outlet terraces and a no-barrier control. Two sizes of plots were established. One replicate consist of plots measuring 30.5 X 15.25m, each of which was instrumented with flumes, samplers and dataloggers for measuring and sampling runoff and sediment. Three replicates are made up of plots measuring 18 m X 10 m for yield determinations. Hedgerows and terraces were established in April and May 2002. Baseline data on soils were collected. Sweet corn (Zea mays) variety Silver Queen was planted on June 4, 2002 and harvested on August 22, 2002. On April 23 and May 12, 2003 sweet corn was planted and failed to grow normally. On June 26, 2003 cowpea (Vigna unguiculata) was planted to replace corn and was harvested on September 3, 2003. Sweet corn was planted on April 20, 2004. Blackberry, variety Kiowa, was replanted on November 15, 2002 due to high die-off of initial seedlings. Gaps in mimosa rows were replanted with potted plants on November 15, 2002. Rye (Secale cereale) was planted as a winter cover crop on October 28, 2002 and on September 30, 2003. Mimosa was pruned in July 10, 2003 and April 16, 2004. Switchgrass was mowed once on March 17, 2004. Prunings were left on the field along the hedgerows. Blackberry fruits were harvested from June 26 to July 22, 2003. Nitrogen, P and K were applied at 180-60-60, 90-60-60 and 90-60-60 kg ha-1 respectively during 2002, 2003 and 2004 cropping seasons on corn and cowpea. Thirty-five kg N and 45 kg Ca ha-1 were applied on blackberry in 2002, 70 kg N and 90 kg Ca ha-1 were applied on blackberry during 2003 and 2004 cropping seasons, respectively. Lime was applied at 3.4 Mg in the fall 2001, at 2.24 Mg ha-1 in 2002 and 2003. Runoff and sediment data were collected from fall 2002 to winter 2004 and analyzed for NO3-N, NH4-N, total N and P. Sweet corn ear and cowpea grain yields were determined as well as nutrient uptake. Results and Conclusions
Rainfall amounts associated with runoff from plots were 189, 491 and 103 mm, respectively, for 2002 (August to December), 2003 (entire year) and 2004 (1st quarter). During 2002, total runoff was highest in the plot with mimosa, followed by control, switchgrass and terrace. Due to technical problems, data were recorded on blackberry plot only for one storm event. During 2003 and 2004, highest runoff was in the control plot, followed by mimosa, blackberry, switchgrass and terrace. Total sediment yield followed almost the same pattern as for runoff except that measured sediment in terrace plot was higher than in switchgrass plot during 2002. Sampling did not occur during the three storm events in 2004. During 2002, highest total P loss in runoff water and sediment was measured in the control followed by mimosa, switchgrass and terrace. During 2003, highest total P loss was measured in the control, followed by blackberry, mimosa, switchgrass and terrace. Total N loss was highest in the control plot followed by blackberry, mimosa, switchgrass and terrace during 2003. Samples were insufficient to perform this analysis during 2002. During 2002, highest total ammonium-N loss in runoff water and sediment was measured in terrace followed by switchgrass, mimosa and the control. During 2003, highest total ammonium-N loss was measured in blackberry, followed by control, mimosa, terrace and switchgrass treatments. During 2002, highest total NO3 loss in runoff water and sediment was measured in the control followed by terrace, mimosa and switchgrass. During 2003, highest total NO3 loss was measured in the control, followed by mimosa, blackberry, terrace and switchgrass. In the 2002 cropping season, treatments had no effect on number of marketable sweet corn ears, ear fresh weight or nutrient content of ears. The 7 % reduction in sweet corn population in alley and terrace plots relative to the control did not significantly affect sweet corn yield. During the 2003 cropping season, cowpea yield and nutrient content were not significantly affected in alley and terrace plots. Average blackberry yield in 2003 was 345 kg ha-1, which is normal for the first two years of plantation. Mimosa dry leaves and stems biomass yield were 50 and 20 kg ha-1 containing 4 and 2%N, respectively. Work planned for 2004 Sweet corn and blackberry will be harvested during 2004. Monitoring of runoff and sediment will continue throughout the year. Agronomic and economic analyses will be completed. Publications/Outputs Dissertation and 2 manuscripts for refereed journals in preparation. One abstracts for conference proceedings submitted and one in preparation. |
