Improved N Fertilizer Recommendations Via An Internet-Service for Site-Specific Simulations of N Uptake, Soil Water and N Dynamics.

In order to further improve N fertilizer efficiency while maintaining crop yields it is crucial to include estimates of current net N mineralisation and current N uptake into N fertilizer recommendations. High dependence of both processes from management and site characteristics as well as extreme year-to-year weather variations have been major obstacles for achieving reliable estimates. However, nowadays field-scale soil and weather input data are available on digital maps (e.g. scale 1:5000 for soil map of NW-Germany) and farmers generally keep field record systems. Thus it was intended to develop and parameterize a model based on these kinds of input data for online simulations via an internet service.

The model with the three main modules soil water, net N mineralization and N uptake was developed using several field trials with winter wheat in four consecutive years, 2006, 2007, 2008, and 2009, in typical areas of NW-Germany. The soil water module follows a simple storage approach with three layers, was parameterized using lysimeter sets and field measurements, and also generates estimates for N leaching. The net N mineralization module was developed using long-term laboratory incubations and field mineralization measurements. It calculates estimates for N release from soil organic matter as well as for immobilization of fertilizer N. Input data for this module are soil, management and weather data. The module for N uptake was parameterized using measurements of plant dry matter, N content, leaf area index (LAI) and N concentration and follows the light use efficiency approach.

Fertilizer recommendations are based on current soil mineral N in the upper 90 cm calculated with the combined model, which sufficiently matched measured values in the field trials and eight farmers’ fields (on an average close to the 1:1-line). In case calculated values fall below a certain threshold, prompt fertilization is recommended.