The article explores the significance and impact of organic matter on the fertility of dark chestnut soil and black soil in the southern regions under irrigation and without irrigation. The aim was to determine the effect of organic fertilizers on the content of humus, water-physical properties, and other fertility indicators. Research conducted at the Institute of Irrigated Agriculture established that without manure in crop rotations with alfalfa, the organic matter content decreases, especially in irrigated plots. After 30 years of observation, the maximum organic matter content was found with optimal application of mineral fertilizers and manure. Irrigation positively affects the mineralization and humification of organic substances, but without irrigation, the humus content is higher due to significantly lower nutrient leaching. Without the application of mineral fertilizers, there is a decrease in total forms of nitrogen, phosphorus, and potassium, including in irrigated soils. Mineral fertilizers increase phosphorus content, but potassium remains at a low level. The results indicate the necessity of a systematic approach to fertilization to maintain and preserve soil fertility. Applying organic materials, such as wheat straw, improves the soil's water absorption capacity and promotes microbiota development. Growing alfalfa accumulates a significant amount of organic matter and biological nitrogen; however, in the absence of livestock farming, it is suggested to sow annual leguminous crops, which are crucial for sustainable production and enhancing soil fertility. Irrigation significantly increases crop yields; however, it also substantially increases nutrient leaching, necessitating additional compensation. The use of available organic materials improves the physical properties of the soil, particularly its structure and water absorption capacity, which is critically important in increasing aridity and climate change prevention. A comprehensive approach to soil fertility management is proposed, including the mandatory use of organic fertilizers and the cultivation of leguminous plants in crop rotations.