Diagnostics of the N:P ratio in the arable soils of the­ Left Bank Forest Steppe of Ukraine

Abstract

Goal. To determine the N:P ratio in soil, fertilizers, and plant products under different conditions of moisture supply for the further development of climate-oriented crop fertilizer systems. Methods. The research was conducted on a 24-hectare soil-agrochemical landfill during 2018–2020, in a temporary field experiment in areas with different levels of moisture supply (2021), as well as in a stationary field experiment established in 1969 on the territory of the State Enterprise «SE «Hrakivske» of NSC «ISSAR named after O.N. Sokolovskyi» (Kharkiv district, Kharkiv oblast). Field methods were used to conduct short- and long-term observations in field experiments; laboratory-analytical — to determine the mobile forms of phosphorus and potassium in the soil after extraction of 0.5 n CH3COOH using the Chyrikov method, nitrate nitrogen — photometrically with disulfophenolic acid, ammonium nitrogen — photometrically with Nessler’s reagent, statistical — to conduct dispersion and regression analysis using the STATISTICA software. NPK content in plants was determined after ashing with a mixture of sulfuric and perchloric acids. Results. Stoichiometrical regulation of the availability of N and P in the conditions of weather and climate fluctuations and increasing shortage of mineral fertilizers is an important direction for increasing the efficiency of fertilization, stabilizing high levels of field crops, and predicting the cycles of biophilic elements in the future. On the territory of the landfill with an area of 24 hectares, separate locations with a significantly higher N:P ratio in the arable layer due to an increase in the concentration of mineral nitrogen were found, the location of which mostly coincided with areas of soil moisture accumulation (r=0.52–0.55). A positive correlation between the N:P2O5 ratio in the soil and its moisture supply (r=0.49–0.53) was determined within the soil areas differing in moisture conditions, and the positive effect of adjusting this indicator on soybean yield was proven. In areas with better moisture conditions before sowing, the highest yield of soybeans was obtained with N180P60K60 fertilizer dose, with lower moisture reserves — with N120P60K60 dose. Conclusions. Adjusting the ratio of N:P2O5 in the soil by managing its nutrient status, i.e. applying different doses and ratios of NPK, taking into account the level of soil moisture, influenced the yield of crops and the stoichiometry of nutrients in plants. The optimal ratios of N:(RC) for growing soybeans in the composition of fertilizers and soil in areas with different levels of moisture supply were determined. An extended N:P ratio was established in the main and by-products of field crop rotation in wetter years.