Mineral nitrogen in spring in two cropping systems with permanent nitrogen supply

Abstract: The purpose of this study is to find out nitrogen (N) transformation in rotation system from previous crop to succeeding crop in both conventional cropping system and conservation tillage cropping system. The conservation tillage cropping system used some methods like legumes and catch crop with lower inputs of fertilizers and pesticides. Mineral nitrogen (Nmin) was measured under permanent nitrogen supply in both cropping systems in early spring time. Soil samples were collected in March and April in southern Sweden. High content of Nmin was found in field B2 which might be positive for N supply to the crop growing in 2012, but also could be a risk for N leakage if the precipitation is very high. The reasons for this condition might be two due to the previous crop Faba bean in this field. First Faba bean does not recover Nmin from soil, and second Faba bean has residues of plants with high N content. After growing winter wheat, in deep soil layer there was low content of Nmin; and also after growing winter rape seed and spring rape seed, there was low content of Nmin as well. In addition, conservation tillage cropping system had high Nmin. High Nmin in spring has possibility to reduce input of N fertilizers, but massive Nmin in soil may pose a risk for N leakage to contaminate nearby seas and lakes when precipitation is high and crops are growing slowly. This study has practical significance for helping farmers choose correct crops and right management to control Nmin content in different soil layers, for preventing N leakage and keeping balance between cropping systems and environment.