During a three-year period (2002-2004), studies were carried out on nitrogen dynamics and losses during cultivation of winter wheat as influenced by disease and insect attacks. Three treatments with different degrees of plant protection (fungicides and pesticides??) were tested in a field trial on a silty clay soil in south-western Sweden. The wheat crop was continually inspected for pests and diseases. Direct measurements of nitrogen leaching were performed in tile-drained field plots equipped with individual collectors for drainage water. Ammonia emissions from the wheat stands were measured in one replicate plot during the first two growing seasons. Nitrogen accumulation and distribution in plants were investigated by sampling the crop at different stages of development and analysing different plant parts for total nitrogen content. Soil mineral nitrogen was determined within the 0-90 cm soil layer in early spring, at yellow ripeness and in November. Grain yield and grain nitrogen efficiency were always significantly larger and mean residual soil mineral nitrogen levels (at maturity and in November) significantly lower in the treatments with crop protection. At maturity, total N concentration in the straw was significantly higher in the treatment without plant protection. Mean nitrogen leaching was greater in the treatment without crop protection but the differences were not statistically significant. Ammonia emissions tended to be somewhat smaller in fungicide-treated wheat stands, but were very small in all treatments. The better N use efficiency with crop protection was probably due to a combination of larger N amounts in above-ground plant parts and better N translocation to grain when diseases were reduced.
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