Influence of tillage and nitrogen fertilisation within the rotation on the nitrogen dynamics after faba beans

A combined field experiment and simulation model study was conducted to quantify the nitrogen dynamics in a faba bean - winter barley sequence with two tillage treatments and two levels of nitrogen fertiliser within the rotation. Correlations between nitrate nitrogen values of the soil (N(min)) values around sowing and harvest of beans increased with soil depth, demonstrating the low nitrate uptake capability of faba bean roots particularly in lower soil layers. Effects of tillage on mineralisation and leaching as calculated with a simple simulation model were small and tended towards slower mineralisation and less leaching with reduced tillage, corresponding with slightly higher nitrogen use efficiencies of barley after winter. Estimated decay constants of soil organic matter increased with years and tended towards higher values in the chisel compared to the moldboard plough treatment. Tillage effects on grain yields were not observed, neither with beans nor with barley. Higher N fertilisation in the rotation increased mineralisation and leaching, and reduced nitrogen use efficiency of barley after winter. It is concluded that faba beans are particularly critical when high amounts of nitrate are present at sowing time due to the other crops in the rotation. The retardation of mineralisation by reduced tillage was too small to substantially reduce nitrogen losses under these conditions.