Modeling long-term compost application effects on nitrate leaching

Application of compost to agricultural soils may be beneficial for crop pro duction by increasing soil fertility and supplying plant nutrients, however , any raise of the soil organic matter content may increase the potential f or unintended groundwater contamination by nitrate leaching. In this paper, the effect of long-term compost applications on nitrate leaching, soil org anic matter content, and crop production is analyzed using results of simul ation scenarios for agricultural sites with loamy and sandy soils. Simulati ons were carried out using the Danish Nitrogen Simulation System (DAISY) wh ich describes the nitrogen balance in a one-dimensional soil-plant-atmosphe re system and considers compost type and application rate as well as manage ment and cropping practice. Estimations of hydraulic and solute transport p arameters are based on pedotransfer functions. Data from a 4.5-year period of field experiments with compost applications in northern Germany as well as from laboratory experiments with compost amended soil are used for model calibration. Simulation results suggest that: (i) with respect to nitrogen turnover the differences between compost types (i.e., non-matured and matu red) are small compared to site-specific properties (i.e., soil temperature and water balance) and management practices (i.e., crop rotation) when con sidering a compost application period of 50 years; (ii) with respect to nit rate leaching the effect of different compost application scenarios is high ly sensitive at the sand and relatively small at the loam site; and (iii) r elatively high crop yields and acceptably low nitrate concentrations in the drainage water are obtained at the sand site when applying a combination o f 10 t compost/ha/yr and soil- N-min adjusted mineral nitrogen additions of about 20 kg/ha/yr to a winter-grain dominated crop rotation. Further optim ization may be possible by applying reduced rates of the (economically inte resting) non-matured compost.