Soil nitrogen dynamics in different potato cropping systems

The dynamic of soil nitrogen in potato cropping systems was compared between traditional planting after moldboard plough (TP) and direct mulch planting (DMP) in cover crop stands on two loamy soils in the Swiss midlands. Differences between cropping systems were most pronounced before planting and after planting up to a plant height of 10 cm. TP showed the highest mineral nitrogen content with more than 200 kg N ha-1 in the 0 – 100 cm soil layer. Mineral nitrogen content was 20 – 25 % lower with DMP in dead yellow mustard stands and 60 – 70 % lower with DMP in the overwintering green turnip rape stands. The lower values of DMP are due to a continuous uptake of mineralized soil nitrogen by the overwintering cover crops. In spring the risk for nitrogen leaching was most efficiently minimized with DMP in green turnip rape stands. With TP, this risk was greater compared to DMP, but depended on the duration of the fallow period before planting of the potatoes. After harvest of the potatoes the risk for nitrogen leaching was high and not affected by the cropping system: soil mineral nitrogen content was 75 kg N ha-1, regardless of the system investigated.