Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, Zurich

Dynamics of nitrogen in the soil under no-tillage and ploughing

Over a period of several years, the mineral nitrogen contents of a loamy cambisol at the Inforama Rütti in Zollikofen, Switzerland, were compared within an arable crop rotation without fallow periods using the two cropping systems of «no-tillage» (NT) and «ploughing» (P). In both systems, the plants received the same amount of mineral nitrogen, but only about two-thirds of the recommended norm. With similarly high total quantities of nitrogen mineralised, N mineralization proceeded more steadily and persisted longer under NT than under P. Particularly in the case of no-tillage cereals, this resulted in a higher yield per fertilised N unit. Otherwise, there were fewer differences in N dynamics between NT and P for winter cereal than for sugar beets and maize. Here, the amount of nitrogen mineralised varied quite sharply from year to year, depending on the weather conditions. Thus, nitrogen mineralization under NT slowed down more strongly in cool than in mild springs. Periods of accelerated mineralization of nitrogen were observed under P after the planting of sugar beets and maize, as well as of winter rye after field peas, which led to an increased risk of N loss. With an adjusted crop rotation, the amount of N fertiliser can be slightly reduced after the transition phase to no-tillage in the case of directly seeded winter cereals. Because of the risk of nitrate leaching, maize and sugar beets should not be subjected to excessively high N inputs at planting in the case of either P or NT.

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