Influence of Long-Term Application of Mineral Fertilizers on the Productivity of Field Crop Rotation in the Direct Action and Their Aftereffect
The aim of the investigation was to determine the regularities of the average annual increase in the productivity of a field crop rotation depending on the doses of fertilizers and the agrochemical background both in the direct action and in the aftereffect. The other goal was to determine the recoupment of “new” and residual compounds of nitrogen and phosphorus. The investigation was carried out under conditions of the Central Pre-Caucasian region in 1975-2014. It is revealed that the positive effect of phosphorus on yield compared to nitrogen was higher in the case of annual application of fertilizers. The average annual growth of productivity with the application of nitrogen fertilizers only was 0.06-0.12 t/ha of grain units (2.6-5.1 % in comparison with a control), of phosphorus fertilizers only - 0.23-0.45 t/ha of grain units (9.8-19.1 %). The highest productivity per hectare of crop rotation area was achieved with the application of complete mineral fertilizer. On average over five rotations it was 2.90-3.04 t/ha of grain units (23.4-29.4 % in comparison with the control). In the study of the aftereffect, the efficiency of nitrogen fertilizers did not yield the efficiency of phosphorus ones. The increase in harvest of grain units per 1 ha reached 0.58-1.05 t/ha or plus 18-33 % compared to the control. Prolonged use of fertilizers contributed to the increase in soil fertility that led to the increase in recoupment of a unit of nutrients by the yield due to the aftereffect. As a result, the payment of 1 kg of N, P and K by the yield, when nitrogen only was applied, increased on average 4.3 times; in the case of phosphorus only - 1.5 times; complete fertilizer - 1.4 times. The highest recoupment of a unit of active substance was achieved at the application of phosphorus fertilizers against a natural background. Taking into account the aftereffect, this index in the variant P30 was 17.35 kg of grain units vs. 6.59 kg of grain units in the case of nitrogen application at the same dose. The annual application of 60 kg of phosphorus separately and against the background of NK, as well as 60 kg/ha of nitrogen against the background of PK, was recommended as the optimal doses of fertilizers. The systematic application of nitrogen fertilizer without improving the phosphorous regime of the soil is ineffective.