In the studies established the influence of feeding conditions on nitrogen-fixing ability of new cultivars of Belarusian selection of field clover, lupin and determined the role of organic matter of legumes (stubble-root residue) in changing agrochemical conditions of sward-podzolic light-loamy soil under the influence of leguminous forecrops. A resource-saving system of crop fertilization was developed in crop rotation with 40% of legumes, which allows for reducing energy input connected with application of fertilizers by 30%, making productivity of grain crops higher than 3 t/ha, potato 30 t/ha of high quality due to the use of biological nitrogen, organic matter of legumes, bacterial preparations, rational application of fertilizers, and growth regulators.