Prediction of Soil Nitrogen Supply in Potato Fields using Soil Temperature and Water Content Information

Abstract

This study evaluated different strategies for use of a simple first‐order kinetic model (Nmin = N0[1– e−kt] where N0 is potentially mineralizable nitrogen and k is the mineralization rate constant) to predict growing season soil nitrogen supply (SNS) in potato (Solanum tuberosum L.) fields under cool humid climatic conditions. All strategies considered spring soil mineral nitrogen (SMN) and the labile mineralizable N pool (Pool I), and correction of the value of k was evaluated based on temperature (T) only, or based on both T and water content (θ). The strategies examined: (i) the depth of the soil used; (ii) the choice of k value used for Pool I; and (iii) the replenishment of the mineralizable N pools. Predicted SNS was compared with a field‐based estimate of plant available soil nitrogen supply (PASNS) measured as plant (vine plus tuber) N uptake plus residual nitrate at harvest in unfertilized plots. When k was corrected using T only, the strategies generally overestimated the PASNS. When k was corrected using both T and θ, predicted SNS was not significantly different from PASNS in most cases. The most promising strategy used a depth of 0 to 20 cm, the common depth for tillage, rather than 0 to 15 cm, which represents the actual depth used for soil sampling. This study demonstrated that SNS can be adequately predicted using a simple kinetic model, and that consideration of soil water content was important in predicting SNS even in humid soil moisture regimes.