The specialization of agricultural enterprises in the cultivation of field crops without livestock industry residues makes it possible to use by-products of cultivated crops, along with plant residues, stubble and roots in the 0-60 cm soil layer, as a fertilizer. The studies were carried out in the long-term (from 1950) field experiment on the Chetrosu Experimental Station of the State Agrarian University of Moldova. The soil is Calcareous chernozem, the experimental crop rotation is eight-field (with peas, winter wheat, maize for grain, sunflower). Until 2000, fertilizers were used in the crop rotation to reach a positive balance of the planned crop yield. In the two last crop rotations (2001-2018), fertilizer doses were reduced, limited to the application of ammophos 100 kg.ha-1 by seed and root dressings of ammonium nitrate. At the same time, the by-products of cultivated crops – straw and stalks – were plowed into the soil. With the application of limited doses of mineral fertilizers, the balance of both nitrogen and phosphorus were positive, and the balance of potassium is very intense. The plowed organic mass of by-products and plant residues exceeds the main products on average in peas by a ratio of 2.21, in winter wheat by 3.20, in maize for grain by 2.15, in sunflower 3.65 times and with an annual average of 5.9-9.1 t.ha-1, which is comparable to 65-120 kg.ha-1 of nitrogen, 24-39 kg.ha-1 of phosphorus, or 150 t.ha-1 of half-reabsorbed manure. In this connection, the need arises to revise the fertilizer system of crops in crop rotation, the methodology for calculating fertilizer rates for the planned yield of field crops, taking into account the aftermath of 1-2 predecessors of the crop.