Utilising differences in rooting depth to design vegetable crop rotations with high nitrogen use efficiency (NUE)

Summary

A number of methods involving plant or soil analysis or modelling have been developed to optimise N fertilization of vegetable crops. The methods aim at improving the NUE of each single crop, but do not really consider the crop rotation as such. Various measures can be used to increase the NUE of the crop rotation; measures that can be combined with the methods aimed at optimising NUE of each single crop.
The aims of the paper are to discuss the methods for optimising NUE at the crop rotation level and to present examples of how this can be done. The main methods discussed are 1) how can crops with different rooting depth be optimally placed in a cropping sequence and 2) how can catch crops be introduced to optimise NUE.
Results show that if N left in the soil after harvest on one crop is retained in the soil until spring, it will normally be found in deeper soil layers. Therefore rooting depth of the vegetable crops is important. It is illustrated that by placing deep-rooted crops in the crop rotation preferentially where much N was left in the soil in the previous year can strongly increase the utilisation of the N residues.
It is also shown how catch crops can be used to maintain a high NUE, especially in situations where the farmers choose to grow shallow-rooted vegetables even though much N may be available in deeper soil layers.