Erosion Deteriorates Chernozem Soil Health and Causes Yield Reduction Not Compensated for by Increased Doses of Nitrogen

Erosion affects soil health, nutrient cycling, and ecosystem productivity. Although the physical manifestations of erosion are well known, further research is needed to understand how its biochemical consequences interact to limit soil functionality and plant productivity. We investigated this in erosion-threatened chernozem soils of the Czech Republic using a pot experiment and a synthetic soil quality index (SQI) with Festuca rubra under varying nitrogen fertilization rates (0–250 kg N ha−1). Erosion significantly degraded soil biochemical quality, reducing soil organic carbon content from 1.40% to 0.78% (p < 0.001) and total nitrogen content from 0.15% to 0.13%. Microbial functions were severely disrupted, as evidenced by a 57% decrease in dehydrogenase activity (p < 0.001) and a 35% decrease in urease activity (p < 0.001). From a production perspective, erosion significantly reduced plant biomass (p = 0.004) across all treatment groups. While nitrogen fertilization significantly stimulated biomass production up to an intermediate rate of 50 kg N ha−1 (p < 0.001), higher application rates led to a strict yield plateau. These results demonstrate that erosion-induced deterioration of the soil’s biochemical complex acts as a primary constraint on crop growth, which cannot be compensated for by increasing doses of mineral nitrogen fertilizer.