Optimizing Fertilizer Applications for Organic Agriculture

摘要

If organic agriculture is to be sustainable, it must consider management strategies that apply over the long term. This paper presents a linear model for optimally scheduling land application rates once a system has approached steady state. Multiple fertilizers and amendments can be included, and solutions can be optimized by minimizing nitrogen leaching, minimizing cost, or by minimizing cost subject to a tolerable leaching constraint. Mineralization is represented using first-order decay models. Several compartments can be associated with each type of incorporated material to simulate the behavior of labile and recalcitrant constituents. Immobilization can also be represented. Once the user determines possible application dates, the approach useslinear programming to assign nitrogen application rates for each material. As an example, the model is applied to a hypothetical Salinas, California operation growing two broccoli crops along with an incorporated rye cover crop. Sea bird guano and cattlemanure compost are available as nutrient sources. Optimization is shown to reduce the leaching potential of an organic farming system while saving money and meeting crop nitrogen supply goals. In the example scenario, when compared to a planning approach consisting of matching applications to 125 percent of crop needs, optimization eliminated a 41 kg ha"1 crop deficit while reducing excess nitrogen from 300 kg ha~(-1) to 274 kg ha~(-1).