Impact of harrowing on the nitrogen dynamics of plants and soil

Harrowing in cereals is usually carried out to control weeds. In this study, the effects of loosening and aerating the soil with a spring tine harrow on the mineral N content of the soil (NO3− and NH4+) and the N content of the crop were investigated. The experiment was conducted in weed-free summer wheat comparing intensive mechanical treatment with an untreated reference in two consecutive years (1999 and 2000). Each year, during the treatment period, both plant and soil samples were analysed in a dense temporal pattern. When the soil was loosened, its average mineral N content in the 0–30 cm layer was enhanced by only 1.1 and 1.3 kg N ha−1 in 1999 and 2000, respectively. The concurrent N uptake of the crop was reduced by 1.2 kg N ha−1 in 1999 and 2.2 kg N ha−1 in 2000. This small effect was attributed to reduced N uptake and not to enhanced N mineralisation. We concluded that harrowing had only a minor effect on the crop nutrient status.