The changes of soil mineral nitrogen observed on farms between autumn and spring and modelled with a simple leaching equation

Abstract

Abstract: The content of nitrate or mineral nitrogen (Nmin = N-NO3- + N-NH4+) in soil in autumn is recognized as the indicator of potential risk of N leaching during winter. In this contribution, the apparent changes of Nmin in the 0-60 cm soil layer, during winter, on farm fields in the Czech Republic were calculated. A significant positive relationship between Nmin in autumn and the change during winter was observed in eight out of the nine farms. Nitrate N data produced similar relationships as Nmin. The regression analysis suggested that 40-90% of Nmin above a specific amount, 14-35 kg N/ha (interception of regression line, I1), on farms was apparently lost from the soil zone. Corresponding results for pooled data (n = 187) were 74% and 25 kg N/ha (r = 0.90, P 0.001). The proportion of N leached from the 0-60 cm layer, calculated with a simple leaching equation was significantly correlated (n = 187, r = 0.92, P0.001) with observed Nmin change during winter, with the intercept (I2) significantly different from zero (-30.9 kg/ha). When the average value of regression intercept I1 of farms, or of pooled data, were introduced to the leaching equation as a constant correction parameter, the fit was satisfactory (r = 0.93 and 0.92, resp.) and the intercepts (-3.1 kg and -5.4 kg N/ha, resp.) were not significantly different from zero (at P 0.01). The results of the study support the use of autumn Nmin within the leaching equation as a robust indicator of the risk of N leaching.