The long-term effect of legumes as forecrops on the productivity of rotation (winter rape-winter wheat-winter wheat) with nitrogen fertilization

A field experiment was carried out in the years 2012-2018 in Poland in a split-plot design. The aim of the study was to determine the long-term effect of legumes as forecrops on the productivity of rotation with nitrogen fertilization. The rotation included: legumes + spring barley (SB), winter rape (WR), winter wheat (WW) and winter wheat. The study was conducted as a two-factorial field experiment with four replications. The present study showed that legumes as forecrops increased the yield of all after-harvest crops in rotation. Yielding of these crops also depended on nitrogen fertilization and position in the rotation. After comparison of the influence of nitrogen fertilization on yield of cereals, it was observed that the effect of this factor was greater for WW cultivated in the fourth year of rotation than for WW cultivated in the third year of rotation. In relation with control, each dose of nitrogen fertilization caused a significant increase of WR and cereals yield, but the dose of 180 kg N/ha did not increase yield significantly in comparison to the dose of 120 kg N/ha. There was also negative agronomic N-efficiency observed between doses of 120-180 kg N/ha, which means that it is not necessary to use 180 kg N/ha, especially if there are legumes in crop rotation.