Nitrogen effects in sugar beet growing: A module for decision support

PIEteR is a field-specific production model for sugar beet growing in The Netherlands, developed as a basis for decision support, for example in nitrogen fertilization. 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 were modelled as functions of nitrogen availability, defined as (N-fertilizer rate + N-min,N- 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 N-min-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 result decreased by about 2% and the explained variances increased by about 15% by including the N-module.