Apparent nitrogen mineralization and recovery of nitrogen supply in field trials with vegetable crops

Abstract

SummaryA major cause of uncertainty in predicting the demand of nitrogen (N) fertilizer by means of mathematical models is the treatment of apparent net N mineralization (ANM) and apparent recovery rate (REC) of mineral N supply (N fertilizer plus soil mineral N at planting). REC and ANM were analysed in 29 multi-level N fertilizer trials conducted with a range of vegetable crops over a period of 11 years. REC differed substantially between experiments (0.29 to 1.24). ANM ranged from 13;110 to 140 kg N ha–1; it decreased with an increasing N supply, and increased with the time between planting and harvest. A simple regression model was used to predict ANM. The model consisted of both a N supply-dependent and supply-independent term, and used N supply and growing time as input parameters. Whereas the model significantly reduced the variance in measured ANM (r2 = 0.45, n = 129), the residuals showed a considerable variation (standard deviation (SD) = 37 kg N ha–1). It is not feasible to predict N fertilizer demand without predicting net N mineralization and fertilizer recovery. Therefore, the regression model is recommended despite its inaccuracy, which is taken into account by adding a security margin to the fertilizer recommendation.