Possibilities to reduce the application of industrial mineral nitrogen fertilizers in crop rotations of the sustainable farming system by using the biological nitrogen accumulated by green manure crops were evaluated based on the data of stationary experiments performed during the 1997-2005 period in the Voke branch of LRCAF. Investigations were carried out in cereals (barley, barley, winter rye, oat) rotation on a sandy loam Luvisol ( Haplic Luvisols) of low acidity, with medium phosphorus content and high potassium level. It was determined that on the sandy loam the main green manure crops (clover aftermath of the 1st year of use, yellow lupine, uncultivated fallow vegetation) had formed more abundant biomass - 3.10-3.74 t ha -1 of dry matter on average, with which 50.0-83.6 kg ha -1 of nitrogen had been added to the soil. The productivity of green manure catch crops (clover under-sowing, oilseed radish) was lower and exhibited higher variation than that of the main crop plants. In autumn, the biomass of the dry matter reached an average of 1.29-2.14 t ha -1, which added 43.3-48.4 kg ha -1 of nitrogen to the soil. The application of green manure exclusively for winter rye and barley fertilization on the sandy loam soil was not successful - cereal harvest substantially decreased compared to fertilization with mineral nitrogen fertilizers N 80: for winter rye - by 15.6-27.6%, for barley - by 62.2%. A combination of the uncultivated fallow vegetation for green manure and nitrogen fertilizer (N 60) rates reduced by 25% was efficient. This variant of fertilization ensured the highest winter rye grain yield (3.30 t ha -1); grains were also significantly larger (+0.7 g).
