Dynamics of the Humus State of Southern Chernozem with Prolonged Use of Mineral Fertilizers in the Conditions of the Steppe Volga Region

The results of monitoring the dynamics of humus and total nitrogen of the southern chernozem in a long-term stationary experiment with the use of mineral fertilizers are presented. In the first 3 rotations of the grain-to-crop rotation, intensive mineralization of humus was noted in all variants of the experiment. In the conditions of grainsteam crop rotation, this process slowed down, and in the variant with the use of minimum doses of nitrogenphosphorus fertilizers in the 6th rotation, the accumulation of humic substances was revealed. The maximum decrease in humus content at the end of 8 rotations of crop rotation (more than 48 years) was observed in variants with the introduction of medium and high doses of nitrogenphosphorus fertilizers. The use of a minimum dose of fertilizers best compensated for the loss of humus of the southern chernozem during prolonged agricultural use. In comparison with the initial data, negative changes in the qualitative composition of humus were noted in the experiment, expressed in a decrease in the proportion of humic acids. At the end of the 8th rotation, the total nitrogen content in the soil decreased in all variants of the experiment.