The aim of the paper is to study the effect of methods and rates of phosphogypsum application on physical-chemical properties of integrated soil cover. The studies were conducted in Salsk district of Rostov region. The object of research is black southern chernozems (zonal soils) and alkali fine soils, which make up integrated soil cover with more than 35 % alkali. According to the scheme of the experiment, the effect of phosphogypsum on alkali and zonal soils properties at the background of deep tillage by application of accepted (overall application) and proposed (selective application) practices on soil complex has been studied. The studies revealed that the alkalinity decreased faster in chernozems than in alkali soils. This is due to the fact that a higher sodium absorption ratio in solonetz (by 28–30 %) restrained the alkalinity processes. At the same time the alkalinity decrease was observed on chernozems at a dose of 5 t/ha of phosphogypsum in the fifth year of aftereffect, and on solonetzes the alkalinity restoration took place by the same year. 10 t/ha of phosphogypsum application on chernozems does not increase the process of its decline and solonetzes soils became weakly alkaline at this dose by the third year, with 5 t/ha of phosphogypsum they became medium alkaline (1.26 mmol/100 g soil), by the fall of the fifth year they became non-alkaline. The composition of the soil absorption complex (SAC) under the control has not changed on chernozem and solonetz. In the reclaimed options on chernozem the amount of Ca approached the optimal parameters and was 74–78 % of the soil absorption complex, and the content of exchangable Na was 2 %, that also corresponds to the optimal parameters by the fifth-year autumn. The best results of ameliorating aftereffect on solonetz were obtained in variants with ameliorant rates of phosphogypsum 10 t/ha. By the continuous application the calcium content in soil absorption complex increased by almost 41 %, while the proportion of magnesium and sodium decreased respectively by 33 and 58 %. The data is similar by the selective application. It has been proved that in order to save and avoid additional chemical load on the chernozem it is advisable to apply a selective way of ameliorant application.
Keywords: integrated cover soils, chemical reclamation, phosphogypsum, alkalinity, solonetzicity, soil absorption complex.
