Influence of phosphogypsum on the chemical composition of aqueous extract from soil

Crop irrigation on chernozems inappropriate to ecological requirements is often accompanied by degradation changes of soils: flooding, secondary salinization and soil alkalinity, destructurization, violation of gas regime, dehumidification, etc. Thus the necessity occurred to study comprehensively the changes in agroecological state of soils, having been irrigated with mineral water under conditions of the Northern Steppe of Ukraine. It has been proved that the irrigated soil solonization is a widespread negative process on irrigated lands, which is determined by the qualitative composition of irrigation water, the initial soil properties, which determines their anti solonization buffering, depth of occurrence, and mineralization of groundwater. According to the latest publications, the area of irrigated solonizated soils of Ukraine is almost 800 thousand hectares, of which more than 700 thousand hectares are poorly solonizated, about 90 thousand hectare are medium and high solonizated. Field experiments, based on the state enterprise “Experimental farm of Dnipro experimental station of the Institute of vegetable and melon growing of the National Academy of Sciences of Ukraine” (Oleksandrivka village of Dniprovsky district, Dnipropetrovsk region, 2010‒2015), included 4 variants and two factors: phosphogypsum application as a chemical ameliorant by various dosages under irrigation and without it. Analysis of the water extraction of soil in all variants of experiments showed an increase in water-soluble salts (sulfates by anions, calcium by cations) when calcium-containing meliorants are introduced. However, phosphogypsum application with different dosages did not significantly affect the type of soil salinity. In all experiments with phosphogypsum application the largest number of anions was in sulfate type of salinity, and cations in sodium one, which is explained by the inflow of these ions with irrigation water and phosphogypsum. Exceptions are checklists. According to the content of toxic salts, all variants ranged from 0.3% to 0.6%, that is, according to the sulfate type, they were characterized by an average degree of soil salinity. The introduction of phosphogypsum on irrigated alkalinized soils under irrigation and without it, leads to an increase in the total amount of salts in the soil layer of 0 to 15 cm in comparison with the initial parameters (up to 4.22 meq/100 g of soil). When phosphogypsum was applied at a rate of 6 t/ha without irrigation, salt accumulation in the layer 45‒60 cm was observed, and when irrigated and introduced phosphogypsum at a rate of 3 t/ha salt was concentrated in a layer of 75‒60 cm. In the soil layer 90‒105 cm, the amount of salts was leveled to the initial conditions. Chemical melioration results to increase Ca+2 ions throughout the soil profile. Concentration of sodium ions in the application of phosphogypsum in the arable soil layer decreased by 30‒37% due to the increase of calcium ion and displacement of sodium sulfate in the lower horizons.