Optimal dose of phosphorus fertilizers for grain agrocenoses in Ob region

The need to intensify the agricultural sector to ensure the food security of the growing population of the planet against the background of depletion of natural sources of phosphorous raw materials leads to an increase in the costs of agricultural producers for phosphorus fertilizers (PF), which increases the urgency of the problem of optimizing the doses of the latter. Based on the generalization of the results of long-term field experiments, the economic and environmental validity of different approaches to calculating doses of PF for cereals in the Ob region was compared. The study was conducted in 2006–2017 in long-term experiments of the SFNCA RAS on leached medium loamy medium humus chernozem in the Central forest steppe of the Ob region (54°53ʹ13.5ʺ n. w., 82°59ʹ36.7ʺ e. l.). Calculations were performed based on the results of observations in 3 crop rotations: 3-field grain-fallow (fallow–wheat–wheat), in 4-field grain-fallow (fallow–wheat–wheat–barley), in 4-field grain-fallow (fallow–wheat–wheat–wheat). The duration of the experiments was 18, 23, 38 years, respectively. The experiments were carried out against the background of nitrogen fertilizers with a complete scheme of plant protection from harmful organisms. A high agronomic efficiency of PF application has been established: the increase in grain yield with the use of P15–P30 averaged 0.5–1.2 t/ha. Phosphorus removal by the grain harvest (its alienation from the field) in the control variants was ≈20 kg P₂O₅/ha of the crop area, in the variants with fertilization it reached 30 kg/ha. Its removal by aboveground biomass was 1.6 times greater and reached 48 kg/ha. The phosphorus balance in the soil in the variants of experiments without the introduction of PF was deficient (–15…–27 kg/ha), with the introduction of P15 its deficit was –11 kg/ha, with a dose of P30 the balance was positive, i. e. the phosphorus intake was excessive. Two indicators were considered as evidence of excess doses of PF >P30 for grain agrocenoses in the forest steppe of the Ob region: accumulation of mobile mineral phosphorus in the soil and an increase in the fraction of enzymatically available phosphorus, these pools can become a source of phosphorus losses from agrocenosis. It is concluded that for the leached chernozem of the Ob region, the calculation of doses of phosphorus fertilizers based on the amount of phosphorus alienation by the grain harvest is more justified from an economic and environmental point of view in comparison with the calculation based on the amount of removal of the element by the entire aboveground (grain + straw) biomass of plants.