The Importance of Humus in the Fertility of Irrigated Gray-Earth Soils and the Effectiveness of Mineral Fertilizers

Humus is an important component of the soil that plays a crucial role in the agricultural ecosystem. A comparative assessment of the current humus state of typical, light gray and meadow-gray soils is given. The study presents the influence of natural factors (altitude above sea level, depth of groundwater) and anthropogenic factors (duration of irrigation, type of agricultural crop) on the quality of humus (group composition) in the studied soils. The influence of the humus state of the soil on the effectiveness of mineral fertilizers was studied in separate observation sites. We revealed that the content and quality of humus in gray-earth soils increases with the height of the soil above sea level. In terms of humus state, typical serozems are superior to light serozems. Moreover, the difference between the group composition of humus of automorphic and semi-hydromorphic soils was studied. We noted the high content of humic acids in the group composition of humus of meadow-gray soils, which provides a better quality of humus compared with light and typical gray soils. As the irrigation prescription increased, an improvement in the quality of humus was observed in all the studied soils. Long-term cultivation of gray-earth soils with irrigated green farming affects not only the accumulation of organic matter, but also an increase in soil fertility, including the effectiveness of the use of nutrients by cotton from mineral fertilizers introduced into these soils. This is especially evident in aphthomorphic soils. The research showed that the utilization rate of nitrogen from nitrogen fertilizers improves with an increase in soil hydromorphism, which indicates the need for differential use of nitrogen fertilizers, taking into account the genetic characteristics of the soil. It is recommended to reduce the norms of nitrogen fertilizers by applying a correction factor.