Agrobiological Evaluation of Microbiologically Processed Cattle Manure on Soil Properties and Spring Wheat Productivity in Northern Kazakhstan

Under rainfed conditions of Northern Kazakhstan, the effects of microbiologically processed cattle manure (CCM) on soil agrochemical and microbiological properties, yield structure, and spring wheat productivity were evaluated over two contrasting growing seasons (2024–2025). Field experiments on chernozem soils tested manure rates of 5–30 t ha−1. Favorable hydrothermal conditions in 2024 enhanced fertilizer efficiency compared with the drier 2025 season. CCM application increased soil nitrate nitrogen from low (<8 mg kg−1) to medium levels (8–12 mg kg−1), while available phosphorus and potassium increased by 15–35% relative to the control across key growth stages. The abundance of major functional microbial groups increased by 1.5–3.0-fold, particularly nitrogen-transforming and cellulose-degrading microorganisms. Grain yield improved significantly in both years, with the highest and most stable yields observed at 15–20 t ha−1, resulting in yield gains of 18–32% compared with the control. Yield improvements were associated with increases in grain number per spike (up to 25–27 grains) and grain weight per spike (up to 1.42–1.62 g). Higher manure rates (20–30 t ha−1) did not confer additional yield benefits. Overall, these findings indicate that moderate CCM application effectively enhances soil fertility, stimulates microbial activity, and improves wheat productivity under dryland conditions.