Cropping system and residue management effects on nitrate leaching and crop yields

The effect of cropping system and of crop residue management on crop yield and N uptake and on NO3 leaching was tested in a 2-year lysimeter experiment with sandy loam soil. One cropping system included a 4-year rotation of spring barley, ryegrass, winter wheat and sugarbeet. In the other system, two test crops of spring barley followed cereal lye, ryegrass or spring barley, grown continuously for 9 years. In the first autumn, straw was incorporated or removed in lysimeters previously in cereals, and sugarbeet top was returned or removed in lysimeters previously in sugarbeet. Lysimeters with and without straw incorporation received I g N-15 m(-2) Of 99 at.% (NH4NO3)-N-15 in order to estimate N immobilization caused by straw and its potential for remineralization. In the second year, above ground residues (except for stubbles) were removed in all lysimeters. Straw incorporation caused more N-15 to be retained in the soil but the leaching of total N in the first winter was not reduced significantly. The pooled NO3 loss over the two winters was not affected by the straw management. Between 12 and 48% of N-15 immobilized by the straw was remineralized during the 3 years following straw incorporation. Sugarbeet top increased the leaching of N in the two winter periods. Losses were small from lysimeters with ryegrass but turnover of ryegrass residues appeared to enhance losses of NO3 in the second winter after its incorporation. Straw incorporation reduced the yield and N uptake of the first test crop of barley, indicating a prolonged N immobilization phase, Sugarbeet yields were unaffected by straw probably because of its longer growth period. Return of sugarbeet tops increased the yield and N uptake of the two succeeding crops. Spring barley grown after termination of permanent ryegrass yielded considerably batter and had larger N uptakes than barley succeeding cereal crops. Despite the differential effects of residue management, the type of cropping system was much more decisive for total N turnover. Amounts of N exported in the crop rotation by NO3 leaching and plant uptake generally balanced the amounts of N applied in mineral fertilizer. More N was exported than applied, however, when spring barley was grown continuously. Incorpora tion of straw could only partly prevent the negative N balance. (C) 1998 Elsevier Science B.V.