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Title: Recommendations for nutrient management plans in a semi-Arid environment

item Shouse, Peter
item Poss, James
item Bradford, Scott

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2010
Publication Date: 5/15/2010
Citation: Segal, E., Shouse, P.J., Poss, J.A., Crohn, D.M., Bradford, S.A. 2010. Recommendations for nutrient management plans in a semi-Arid environment. Agriculture, Ecosystems and Environment. 137(2):317-328.

Interpretive Summary: The US Environmental Protection Agency currently requires that application of wastewater and manure from Concentrated Animal Feeding Operations (CAFOs) to agricultural fields follow an approved Nutrient Management Plan (NMP). This manuscript reports on results from field experiments that were conducted to investigate the transport and fate of nutrients and salts under a well-designed and implemented NMP in a semi-arid environment. Results indicate that optimal NMPs will (i) utilize CAFO wastewater that is dominated by inorganic N forms, (ii) apply wastewater to soils with low values of organic N, and (iii) leach salts following harvests rather than prior to planting. This information will be of use to farmers and regulators who are concerned with maximizing crop productivity and protecting groundwater under NMP conditions.

Technical Abstract: A nutrient management plan (NMP) field experiment was conducted to investigate the fate of nitrogen (N), phosphorus (P), potassium (K) and salts in a semi-arid environment (San Jacinto, CA). Our mechanistic approach to study NMP performance was based on comprehensive measurements of water and N mass balance in the root zone. A cereal crop rotation (wheat-rye hybrid to sorghum, Triticum aestivum L.–Secale cereale L. to Sorghum bicolor L. Moench) that does not fix atmospheric N was employed during 2007, whereas a legume crop (alfalfa, Medicago sativa L.) that forms nodules to fix N was used in 2008. Blending (2007 and 2008) and cyclic (2007) dairy wastewater (DWW) application strategies (no statistical difference in 2007) were implemented to meet crop water and N uptake. The high content of salts in DWWand accurate application of water to meet evapotranspiration (ET) yielded salt accumulation in the root zone. Leaching these salts after the fallow period resulted in the flushing of nitrate that had accumulated in the root zone due to continuous mineralization of soil organic N. This observation suggested that a conservative NMP should account for mineralization of organic N by (i) leaching salts following harvests rather than prior to planting and (ii) maintaining soils with low values of organic N. For the wheat-rye hybrid–sorghum rotation, losses of nitrate below the root zone were minimal and the soil organic N reservoir and P were depleted over time by applying only a fraction of the plant N uptake with DWW (28–48%) and using DWW that was treated to reduce the fraction of organic N (3–10%), whereas K accumulated similar to other salts. Conversely, with alfalfa approximately 15% of the applied N was leached below the root zone and the soil organic N increased during the growing season. These observations were attributed to fixation of atmospheric N, increased root density, and applying a higher fraction of plantNuptake withDWW(76%). Collectively, our results indicate that NMPs should accurately account for water and nutrient mass balances, and salt accumulation to be protective of the environment.