Agrochemical Indicators, Content and Reserves of Mobile and Nonexchangeable Potassium Forms in the Profile of Arable Soddy-Podzolic Soil of a Long-Term Experiment with Introduction of Increasing NPK Doses

Abstract

The aim of the work is to study the effect of increasing doses of NPK on the change in agrochemical parameters and exchangeable and nonexchangeable forms of potassium along the profile of sod-podzolic soil. The results of studies obtained in a stationary field experiment in 1978 of laying on sod-podzolic heavy loamy soil of the Cis-Ural region are summarized. The introduction of increasing doses of complete mineral fertilizer from 30 to 150 kg a.i./ha in an eight-field crop rotation was studied. It has been established that the application of NPK at the rate of 60–150 kg a.i./ha, together with the plowing of straw, contributed to the preservation of the initial level of organic carbon reserves in the arable soil layer. The distribution of organic carbon in depth along the soil profile sharply decreases. The use of (NPK)_30–150 led to a significant accumulation of mineral nitrogen in the soil in the arable layer. With the introduction of high doses of (NPK)_120–150, an increase in the amount of mineral nitrogen was noted throughout the entire 1-m soil layer and the reserves increased by 4.0–4.2 times. The use of mineral fertilizer at a dose of 90–150 kg of a.i./ha led to an increase in the content of mobile phosphorus compounds in the 0–80-cm layer. Phosphate reserves in the 1-m soil layer increased by 1.2–1.9 t/ha. The content of readily exchangeable potassium compounds in the arable soil layer increased with long-term application of NPK at 60–150 kg a.i./ha (by 1.8–3.2 times), while the content of mobile increased with the use of NPK at 90–150 kg a.i./ha (1.2–1.4 times relative to the initial level). However, when NPK was introduced, a decrease in the content of the nonexchangeable form of potassium in the 1-m soil layer was observed. Fundamental differences were not established in the nature of the formation of the meter profile of the considered variants of the experiment, depending on various doses of NPK. Comparing the results on the distribution of the main nutrients along the profile of soddy-podzolic heavy loamy soil, it should be noted that the main changes occurred within the upper 0–40-cm layer and were caused by the application of mineral fertilizers.