Response of Plant–Soil–Microbe System to Organic Fertilization in the Composite Soils of Pisha Sandstone and Aeolian Sand

ABSTRACT Aeolian sands are characterized by loose structure and poor water and nutrient retention. Incorporating Pisha sandstone into weathered sandy soils improves texture, water‐holding capacity and cation exchange capacity, potentially reshaping microbial communities and crop performance. However, the role of organic fertilization in such composite soils remains underexplored. We conducted an eight‐month pot experiment in the Mao Wusu Desert with Brassica napus grown in a 1:2 (v:v) mix of Pisha sandstone and Aeolian sand. Organic fertilizer was applied at 0%, 0.4%, 0.6%, and 0.8% of dry soil weight, based on the principles of low quantity effectiveness, high quantity safety, and distinguishable gradients. We measured plant growth and yield, soil total and available nutrients, and soil microbial diversity and functional genes. We found that, organic fertilizer markedly altered soil chemistry and microbiology. At a low application rate (0.4% addition, Y1), available N (NO 3 − ‐N + NH 4 + ‐N) increased by 32.6%, soil pH dropped by 0.8 units and C:N ratio declined by 18.4% versus the unfertilized control. Proteobacteria peaked at 43.6% relative abundance under Y1, exhibiting a unimodal response to fertilization. Redundancy analysis identified NH 4 + and NO 3 − as the main drivers of bacterial community shifts. Y1 suppressed nitrification genes (amoABC −41.2%) while enhancing denitrification pathways, correlating with a 24.7% yield increase. Partial least squares path modeling confirmed that organic fertilizer influenced yield primarily through modulation of soil N cycling. Higher application rates (0.6%–0.8%) reduced available N, limiting plant biomass and yield. These findings underscore the importance of optimizing organic fertilizer rates to bolster soil fertility and microbial function in Pisha–Aeolian sandy complexes without incurring negative agronomic effects.