Influence of different crop rotations on nitrate leaching

The difference in the effects of six crop rotations, grass-clover ley, Miscanthus, and bare fallow on the amount of drainage runoff, nitrate concentration, and the amount of nitrate leached to groundwater was investigated during seven years (1993-1999) using lysimeters (1 m2 surface and 1.4 m usable depth, filled in 1982 with a low humus, loamy sand). The results revealed differences depending on precipitation, rotation, and degree of vegetation cover. Seven-year average nitrate losses of rotations involving cover crops were 85 kg N/ha and thus one third lower than those of rotations without cover crops. Averaged over all six rotations and bare fallow, nitrate concentration during the whole year exceeded the tolerance level for drinking water of 40 mg NO3/l. Different types of pre-cultivation can lead to different nitrate losses during the main cropping period. Thus, with respect to nitrate leaching, the sequence of crops should receive more attention.