Rational fertilization boosts crop yields and enhances nutritional value, but over-fertilization is counterproductive. Furthermore, water eutrophication caused by excessive use of nitrogen fertilizers has become a major agricultural non-point source pollution problem in the Erhai Lake Basin of China. This study took high-fertility soil as the research object and set up six treatments: no fertilization (CK), local recommended fertilization (T1), optimized chemical fertilizer (T2), organic fertilizer replacing 20% (T3), 40% (T4), 60% (T5) of chemical fertilizer with equal nitrogen. The results show that replacement of chemical nitrogen fertilizers with organic nitrogen fertilizers at an appropriate ratio can optimize soil nitrogen supply, enhance the activity of soil nitrogen cycle enzymes, thereby promoting the activity of nitrogen metabolism enzymes and nitrogen assimilation capacity in potato plants, and ultimately achieve a synergistic effect of increased yield, improved quality and higher fertilizer use efficiency. Among the treatments, the nitrate reductase (S-NR) activity in potato leaves was 36.74% and 41.66% higher under T3 than T1 and T4, respectively. For potato quality, Vitamin C (VC) content was 17.41% higher under T3 than T2; soluble protein content was 11.44%, 10.63%, and 9.44% higher under T3 than T1, T2, and T4, respectively. The replacement of chemical fertilizers with organic fertilizers mainly enhances the protein content in potato tubers by increasing soil urease (S-URE) activity and leaf relative chlorophyll content (SPAD) value. Based on the comprehensive differential combination evaluation model, considering potato metabolic absorption, yield, quality, and soil nitrogen content, the T3 treatment is the optimal fertilization method in the Erhai Lake Basin of China.

Aims: This study aimed to evaluate how the combined application of slow-release nitrogen fertilizer and urea influences nitrogen losses via runoff and the yield performance of silage maize in red soil sloping cropland, in order to support region-specific strategies for soil and water conservation and efficient nitrogen management in maize-based systems. Methods: A one-year field runoff plot experiment was conducted under natural rainfall conditions. Three fertilization treatments with equal nitrogen input were established: conventional urea application (CK), 25% controlled-release nitrogen fertilizer combined with 75% urea (P1), and 50% controlled-release nitrogen fertilizer combined with 50% urea (P2). Results: (1) Co-application of slow-release fertilizer and urea significantly improved soil and water conservation compared to CK; total runoff was reduced by 9.17% and 8.29% under P1 and P2, respectively; and soil loss was reduced by 16.45% and 12.25%. (2) The co-application of slow-release fertilizer effectively reduced nitrogen losses from sloping farmland. Compared to CK, both P1 and P2 reduced losses of total nitrogen (TN), nitrate nitrogen (NO₃⁻-N), and ammonium nitrogen (NH₄⁺-N) during the maize growth period, with the reductions under P2 being most pronounced. (3) The co-application of slow-release fertilizer and urea enhanced maize nitrogen uptake and increased maize yield. Conclusions: Based on the results of this single-year field experiment, the combined application of controlled-release nitrogen fertilizer and urea showed potential advantages in reducing runoff-related nitrogen losses while improving crop productivity in red-soil sloping cropland. Among the treatments, P2 (50% controlled-release nitrogen substitution) exhibited relatively better overall performance. However, the broader applicability of these findings requires further verification through multi-year field experiments under different climatic conditions.

Nitrogen application significantly affects microorganisms in agricultural ecosystems. However, it is still unclear how nitrogen application affects soil chemical properties and microbial communities in purple mudstone weathering products. In this study, a field soil column experiment was conducted in a typical purple soil area with four nitrogen fertilizer application gradients of 0 [CK], 280 [N1], 560 [N2], and 840 [N3] N kg ha⁻¹. Nitrogen addition decreased the bacterial chao1 value and increased the bacterial evenness index. For both α- and β-diversity, the effect of nitrogen addition on bacteria was much greater than that on fungi. Nitrogen addition significantly increased the relative abundance of Proteobacteria, Gemmatimonadetes, Bacteroidetes, and Ascomycota and decreased the relative abundance of Actinobacteria, Cyanobacteria, and Basidiomycota. Both pH and TC are the most important soil chemical properties influencing the bacterial and fungal communities. With the increases in the nitrogen application rate, the co-occurrence network complexity increased and then decreased. In summary, nitrogen fertilizer application could significantly change the soil chemical properties, microbial community diversity, composition, and co-occurrence network of purple mudstone weathering products. Among them, the N2 treatment (560 N kg∙ha⁻¹) can more effectively stimulate the soil nutrients, enhance microbial network complexity, and promote further weathering of purple mudstone.