FRACTIONAL COMPOSITION OF MINERAL PHOSPHATES OF PODZOLIZED CHERNOZEM AFTER PROLONGED USE OF FERTILISERS IN FIELD CROP ROTATION

Abstract

The phosphate state of the soil is an important factor in forming its fertility. In this regard, the study of the phosphate state of different soil subtypes in different agrocenoses is relevant. Experimental data on changes in the content of gross phosphorus and its fractional composition in podzolized chernozem under the influence of long-term fertilisation are important for the effective use of fertilisers in the right-bank forest-steppe of Ukraine, determine its potential for providing plants with phosphorus, and are the theoretical basis for clarifying the standards for the rational use of high-cost phosphorous fertilisers. The purpose of the study was to investigate changes in the fractional composition of mineral phosphates of podzolized chernozem compared to fallow after the use of various fertiliser systems in the field crop rotation of the right-bank forest-steppe. In the soil from a layer of 0-20 cm, the content of mineral phosphates was determined by the Chang and Jackson method modified by Ginzburg-Lebedeva with photo colourimetric determination of phosphorus by the Denigs method modified by Truog-Mayer. Studies have shown that the loessial podzolized heavy loam chernozem has significant reserves of phosphorus potentially available for plant nutrition. After 55 years in the field crop rotation, depending on the characteristics of fertiliser, its content in the soil changed from 921 mg/kg to 2,565 mg/kg P2 O5 (content of 1,008 mg/kg under fallow). The content of mineral phosphate fractions in podzolized chernozem is arranged in the following sequence: Ca-PII>Ca-PIII>Ca-PI >Fe-P>Al-P. The use of manure and mineral fertilisers increases the phosphorus content in all fractions of mineral phosphates. First of all, the share of active forms – Ca-PI and Ca-PII is growing up to 66-72% (with 64% content in fallow). According to the organo-mineral fertiliser system (option Manure 13.5 t + N68P101K54), phosphorus between the fractions of mineral phosphates is distributed in the following ratio,%: Ca-PI -7; Ca-PII-40; Ca-PIII-28; Al-P-11; Fe-P-14. Phosphate mobility estimated by the indicator (Ca-PI + Ca-PII): Ca-PIII depends more on fertiliser doses than on fertiliser systems. High content of Ca-PIII fraction in podzolized chernozem indicates the need to clarify the optimal content of mobile phosphorus compounds.