Nikitina O. Changing potassium status of podzolic chernozem at long application of fertilizers in the field crop rotation in terms of Right-Bank Forest-Steppe of Ukraine

Object - relationship between potassium soil state, doses and types of fertilizers and nutrition mode of agricultural crops. Purpose - to determine changes in the potassium state of clay-loam podzolized chernozem in Right-Bank Forest Steppe of Ukraine for a long-term use (50 years) of fertilizers in the field crop rotation. Methods - field, laboratory, mathematical and statistical and calculation and comparative. Theoretical results - the impact of long-term use of different doses of fertilizers and fertilizer systems in the crop rotation on the change in contents of different potassium forms in podzolized chernozem is scientifically grounded; thermodynamic parameters of potassium soil state in podzolized chernozem are determined; a graduation of potassium availability for agricultural crops in the crop rotation is proposed; the coefficient of potassium return in the crop rotation that will ensure its optimum ratio with other elements in the mineral nutrition of plants is grounded and defined; the dynamics of potassium balance in the soil at different doses and fertilizer systems in the field crop rotation is shown. Practical results - optimization measures of potassium mode in the soil and potassium availability for agricultural crops are offered on the basis of research results. It is in order to increase crop productivity of potassium to ensure high economic and energy efficiency. It is recommended for farms with a developed livestock production to return potassium with fertilizers by 80 % of the commercial yield in order to maintain optimum parameters of the potassium soil state. In case of leaving non-market products in the field it is advisable to apply potassium with fertilizers at a dose of 45 kg K2O/ha. To characterize the potassium mode of the specific field, along with mobile potassium compounds, it is recommended to determine the content of soluble potassium compounds in the soil (Dashevsky's method). Novelty - return coefficients with fertilizers of yielded potassium by agricultural crops in the crop rotation to improve or maintain the achieved content of mobile potassium compounds in the soil in the crop rotation of grain and beet type are proposed. Peculiarities of long-term use (50 years) of different doses of fertilizers and fertilizer systems on the potassium supply in the soil and potassium balance in the crop rotation are determined. Changes in thermodynamic parameters of potassium state in podzolized chernozem are defined. It is found that all potassium forms are replenished, especially soluble and mobile compounds, with a prolonged use of fertilizers. It is proved that the increase of potassium content in podzolized chernozem is observed at the dose of potassium application which can be 50 % of its yield in case of leaving non-market products in the field and or 80 % in case of taking out. A graduation of availability of soluble potassium compounds for agricultural crops in podzolized chernozem in Right-Bank Forest Steppe of Ukraine is proposed. It is found that the ratio of Mg : K reduces in the soil absorbing complex in podzolized chernozem when applying potassium fertilizers for 50 years. This indicates the need to apply magnesium fertilizers. It is shown that when there is a long-term use (50 years) of applying potassium fertilizers at the dose of 45-135 kg/ha the specific activity of 40К isotope increases by 12-30 % compared to plots without fertilizers. Degree of application - the main research results were implemented in 2015 on the total area of 4225 hectares at agricultural enterprises in Uman area of Cherkasy region. The field is agriculture.