Nitrogen effects in sugar beet growing: a module for decision support.

PIEteR, a field-specific production model for sugarbeet in the Netherlands, is described. The model was developed as a basis for decision support, for example in determining N fertilizer requirements. Root and sugar yields, sugar content, (K Na) and alpha -amino-N contents, extractability index, operating receipts (a measure for financial returns) and residual nitrogen in leaves are modelled as function of N availability, defined as (N-fertilizer rate Nmin, 0-60 cm (soil, February)), and included in PIEteR as a so-called 'N-module'. Analysis of experimental data showed that root and sugar yield were optimal at 240 and 200 kg N ha-1, respectively. Sugar content and extractability index decreased, and (K Na) and alpha -amino-N contents and fresh leaf yield increased with increasing N-availability. The operating receipts were optimal with 180 kg ha-1, or with a nitrogen fertilizer rate of 130 kg ha-1, assuming an Nmin-amount in soil in February of 50 kg ha-1. The results of the analysis were the basis for the functions in the N-module. In an independent test on data of 100 fields, the prediction errors for root and sugar yields and financial results decreased by about 2% and the explained variances increased by about 15% by including the N-module