Modeling long-term compost application effects on nitrate leaching

Application of compost to agricultural soils may be beneficial for crop production by increasing soil fertility and supplying plant nutrients, however, any raise of the soil organic matter content may increase the potential for unintended groundwater contamination by nitrate leaching. In this paper, the effect of long-term compost applications on nitrate leaching, soil organic matter content, and crop production is analyzed using results of simulation scenarios for agricultural sites with loamy and sandy soils. Simulations were carried out using the Danish Nitrogen Simulation System (DAISY) which describes the nitrogen balance in a one-dimensional soil-plant-atmosphere system and considers compost type and application rate as well as management and cropping practice. Estimations of hydraulic and solute transport parameters 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 matured) are small compared to site-specific properties (i.e., soil temperature and water balance) and management practices (i.e., crop rotation) when considering a compost application period of 50 years; (ii) with respect to nitrate leaching the effect of different compost application scenarios is highly sensitive at the sand and relatively small at the loam site; and (iii) relatively high crop yields and acceptably low nitrate concentrations in the drainage water are obtained at the sand site when applying a combination of 10 t compost/ha/yr and soil- Nmin adjusted mineral nitrogen additions of about 20 kg/ha/yr to a winter-grain dominated crop rotation. Further optimization may be possible by applying reduced rates of the (economically interesting) non-matured compost.