Comparative characteristics of the properties of Halpic Chernozem of the Kursk Region of different land use

Analytical data show that prolonged extensive agricultural use of typical Chernozem of Kursk region (Haplic Chernozem) results in adverse changes in some soil properties. This primarily concerns the humus content and the structural state of the Chernozem. Under the influence of continuous winter wheat growing (for 54 years) the losses of humus made up 24% of its content in virgin soil. The permanent corn growing (for 54 years) led to humus 32% losses, and under the influence of the bare fallow (for 54 years) – 48%. As a result of mineralization of humus, which is one of the main aggregative agents, water resistance of Chernozem structure has deteriorated. The number of water-resistant aggregates in variants with continuous winter wheat and continuous corn decreased in comparison with virgin soil (by 30% and 39% respectively). In terms of water resistance, the structure of Chernozem was transformed in agrocenoses from “extremely high” to “good”. Under the influence of the bare fallow the content of water-resistant units decreased by 75%, and the structure became “non-water resistant”. At the same time, the average diameter of waterproof aggregates decreased 2.8, 3.6 and 4.8 times in variants with continuous winter wheat, corn and permanent bare fallow, respectively, whereas the content of the water peptized clay increased 2.8–4.7-fold, and pH of medium increased by 0.16–0.57. At the same time, the content of soil exchangeable calcium reduced (more than 1.1-fold), as well as hydrolytic acidity (1.1–1.7-fold), the content of organic forms of phosphorus (1.1–1.4-fold) and the ratio of organic forms of phosphorus to mineral ones also decreased 2.1–4.1-fold. When the bare fallow is transferred to the abandoned land, the properties of Chernozem vary with different intensity. The most significant changes occurred with water-resistant aggregates. Their content has increased by 53% over 20 years, and the structure has transformed from “non-water resistant” to “good”, while the content water peptized clay has decreased 2.1 times. During the 20-year period, the content of exchangeable calcium and hydrolytic acidity increased by 1.9 and 1.03 mg-eq/100 g of soil. The content of humus has increased by 0.78%, i. e. humus content restoration occurred with a speed of only 0.04% per year. It is necessary to consider this factor when regulating the humus status of the plowed and eroded soils. In general, the impact of continuous bare fallow on the properties of Chernozem was so profound that 20 years after its transfer to the category of abandoned lands, the properties of Chernozem, in most cases, have been restored only to the level typical of variants with crop cultivation.