Assessment of the influence of mineral fertilisers on the phosphate regime of meadow chernozem carbonate soil and yield of sunflower and winter wheat

The relevance of the study lies in the need to maintain optimal levels of mobile phosphorus in carbonate soils to support healthy plant growth and development, as it can be converted into less mobile forms in such soils. The purpose of the study was to assess the impact of various long-term fertilisation strategies on the content of various forms of phosphorus in the soil to improve this availability. The research was conducted in 2019-2022 as a stationary experiment in a separate division of the National University of Life and Environmental Sciences of Ukraine “Agronomic Experimental Station” in Kyiv Oblast on meadow chernozem carbonate low-humus coarse-sawn light loamy soil in a five-field crop rotation, where the influence of different levels of fertiliser saturation (no fertiliser, minimum, average, and optimal) on soil phosphate status and yield of Etana winter wheat variety and Sumiko sunflower hybrid was investigated. Soil samples were taken from the 0-20 and 20-40 cm layers, and the group and fractional composition of phosphates was determined using the Chang-Jackson method and the content of mobile phosphates using the Chirikov and Machigin methods. According to the analysis of the group and fractional composition of soil phosphates, it was found that in meadow chernozem carbonate low-humus coarse-sawn light loamy soil, the content of iron phosphates prevails among all fractions during long-term fertilisation. The results showed an increase in the content of aluminium phosphates in the 0-20 cm surface layer of the soil of two variants with long-term fertilisation, and an increase in the content of the second fraction of soluble calcium phosphates (Ca-PII), with the minimum saturation (N27P18K20) with the highest available phosphate fraction for plants (Ca-PI) is observed. The content of mobile phosphates was maximal at optimal fertiliser saturation (N81P54K62) and was 4.8 and 8.5 mg/100 g of soil, the aftereffect of organic fertilisers positively affected the accumulation of mobile phosphates in the soil. The highest yield of winter wheat (7.55 t/ha) and sunflower (4.28 t/ha) was obtained with optimal fertiliser saturation, the lowest – without the use of fertilisers, where it was 4.45 t/ha for winter wheat and 2.23 t/ha for sunflower. The results of the study can be used to develop more sustainable and effective strategies for using phosphorus in soils, which can help preserve soil resources and prevent possible contamination of water sources due to excessive phosphorus intake