Nitrogen Regime of Sod–Podzol Soil with Prolonged Use of Different Types and Combinations of Mineral Fertilizers

Abstract

The study investigates the effect of various types and combinations of mineral fertilizers on the fractional composition of nitrogen in sod–podzol soil in a long-term stationary experiment and compares it with a virgin (undisturbed) analog. The studies were carried out on the experimental field of the Perm Research Institute of Agriculture in 2016 and 2018 after harvesting barley in an eight-field crop rotation on sod–podzol heavy loamy soil. The experiment’s design was as follows: without fertilizers: N₉₀; Р₉₀; K₉₀; N₉₀P₉₀; N₉₀K₉₀; P₉₀K₉₀; and N₉₀Р₉₀K₉₀. To assess the effect of nitrogen, phosphorus, potash fertilizers, and their combinations on the nitrogen regime of sod–podzol soil, arable soil was compared with the virgin analog. The nitrogen pool of sod-podzol soil of a long-term station experiment is represented by 64–71% nonhydrolyzable and 17–22% not readily hydrolyzable forms of nitrogen. Long-term use of various types and combinations of mineral fertilizers did not significantly change the ratio of nitrogen fractions characteristic of virgin soils of this type. Nitrogen fertilizers, both in single-strength application and in combination with potassium chloride (N₉₀K₉₀) and superphosphate (N₉₀P₉₀), contributed to an increase in the total nitrogen content in the topsoil layer by 10–20% compared to the control; mineral nitrogen compounds improved the total nitrogen content two- and threefold. Single-strength application of potash fertilizer provided an increase in the content of total nitrogen in the soil by 12%; introduction of superphosphate did not have an appreciable effect on the nitrogen regime of the soil. Long-term use of complete mineral fertilizer (N₉₀P₉₀K₉₀) maintained the total nitrogen at the virgin soil level, that is, 1490 mg/kg. Long-term single-strength application of nitrogen fertilizers increased the content of nitrate nitrogen by 1.5–2.5 times and ammonium by 1.5‒14.6 times in the soil throughout the entire meter layer. In the variants N₉₀P₉₀, N₉₀K₉₀, and N₉₀P₉₀K₉₀, stock of mineral nitrogen increased two- to threefold in the 0–20 cm layer and doubled in the 0–100 cm layer compared the control variant.