Effects of genotype and environment on N uptake and N partition in organically grown winter wheat (Triticum aestivum L.) in Germany

Differences among six winter wheat varieties regarding N efficiency (NE) and its components were assessed in field trials in four locations over 3 years under conditions of organic farming (OF). N uptake and utilization efficiency, redistribution of N vs. direct N uptake during grain filling, N uptake in three periods (tillering, stem elongation/heading and grain filling) and the quantity of mineralized N during the same sub-periods were determined. Significant differences for these traits and significant interactions among varieties and environments could be detected for NE and its components. Limiting N availability during grain filling was typical for the more extensive organic environments. Under these conditions, differences of NE could be attributed to differences in pre-anthesis uptake and in translocation from vegetative tissues to the developing grain. Pre-anthesis uptake contributed more to N efficiency than translocation efficiency. Under more favourable conditions, differences became more evident and were mainly due to direct uptake during grain filling. This confirms, that different varieties are necessary in different environments and that breeding may contribute to improve baking quality to a certain extent. However, utilization of mineralized N is still unsatisfactory in OF systems in Germany. More N efficient varieties alone will help only little to resolve this problem; this can be achieved only by also improving the cropping systems.