Humus state and agrochemical characteristics of soils of the Zhambyl region depending on the type and agricultural use

A comparative analysis of the agrochemical indicators of soils of various types in the Zhambyl region was carried out on virgin and cultivated lands, along with an updated assessment of the humus state using modern agrochemical analysis methods. Patterns of changes in the humus layer and agrochemical indicators depending on the intensity of agriculture and anthropogenic load were identified. It was found that plowing and irrigation lead to a decrease in soil humus content and changes in acid-alkaline and salt properties. The highest humus content is characteristic of light brown carbonate and meadow-saline virgin soils, which is due to a more favorable water regime and accumulation of organic matter. In all soil types, there is a regular decrease in humus content with depth. In arable soils, the humus profile is more even. The total nitrogen content in soils closely correlates with the humus content. The low mobility of humus compounds, characteristic of soils with a predominance of carbonate and alkaline conditions, is indicated by the water-soluble humus content in the studied soil types, which does not exceed 0.001–0.009%. The C:N ratio of 6 to 10 in most of the studied soil horizons of the Zhambyl region indicates a sufficiently high degree of organic matter decomposition and favorable conditions for its mineralization. The content of mobile phosphorus in most of the studied soils is at a low and very low level, which is characteristic of soils with an alkaline reaction and a high calcium content. The good natural supply of exchangeable potassium is indicated by the fact that in almost all soils, potassium is characterized by high values in arable horizons. The soils studied are also characterized by a high degree of base saturation, mainly with calcium and magnesium. Increased sodium content in meadow-saline and irrigated soils can lead to the development of salinity and deterioration of their agrophysical properties. The soil solution is alkaline, and its alkalinity can reduce the availability of phosphorus and micronutrients to plants in arable areas under irrigation conditions. The results obtained confirm the presence of a clear profile differentiation of the humus of soils and indicate a significant influence of both the genetic type of soil and anthropogenic impact on the content and quality of organic matter.

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