Reduced fertilization technology is an eco-friendly strategy to minimize nitrogen (N) and phosphorus (P) surpluses and losses in vegetable production. However, little is known about the performance of chemical fertilizer reduction when supplemented with palm silk biochar (PSB) in subtropical acid soils. A short-term (60 d) field investigation under conditions of in situ incubation was conducted in vegetable farmland in southern China. The treatments included no fertilization (Control), 100% conventional fertilization (CF₁₀₀), 90% conventional fertilization plus 10% PSB-based fertilization (CF₉₀B₁₀), 85% conventional fertilization plus 15% PSB-based fertilization (CF₈₅B₁₅), and 80% conventional fertilization plus 20% PSB-based fertilization (CF₈₀B₂₀). The CF₉₀B₁₀, CF₈₅B₁₅, and CF₈₀B₂₀ treatments had the same inputs of total N and P as the CF₁₀₀ treatment. Reduced chemical fertilization generally decreased the soil NH₄⁺-N regardless of the PSB substitution rate (10%, 15%, or 20%), incubation condition (top-covered or top-open: preventing or allowing the leaching process, respectively), and sampling time (1 day or 60 days). Conversely, compared with the CF₁₀₀ treatment, both the CF₈₅B₁₅ and CF₈₀B₂₀ treatments did not lead to a significant decrease in the NO₃⁻-N concentration in soil under top-open incubation conditions, but significantly (p < 0.05) increased soil NO₃⁻-N under top-covered incubation conditions. The CF₈₀B₂₀ treatment significantly (p < 0.05) decreased soil Olsen-P in comparison with the CF₁₀₀ treatment, regardless of the incubation condition and sampling time. After applying chemical fertilizer in combination with PSB, soil net ammonification and N mineralization tended to be reduced considerably, with substantial reductions of 39–76% and 24–45%, respectively; reversely, soil net nitrification was stimulated by an increased PSB substitution rate. As the rate of chemical fertilization decreased, the trends in NH₄⁺-N and NO₃⁻-N losses from the soil were similar to the trends observed in soil net ammonification and net nitrification, respectively. Additionally, there were no significant differences in the soil net P mineralization and Olsen-P loss between chemical fertilization alone and in combination with PSB application. Generally, the partial substitution of chemical fertilizer with PSB at a low application rate may not substantially reduce plant-available NO₃⁻-N and Olsen-P. It can also contribute to the sustainable availability of N and P in vegetable farmland soil via a variety of transformation processes, such as mineralization, immobilization, and loss.

Lychee is one of the most popular tropical fruits in South China. However, excess fertilizer application is reducing soil productivity and lychee production. Little information is available to develop a rational and feasible recommended fertilization approach for lychee. This study aimed to optimize fertilizer management for lychee production with a nutrient recommendation model that simplifies complex principles of fertilization into a user-friendly "nutrient expert (NE)" system. Analyses of extensive database for lychee revealed that the average yield responses (YRs) of lychee to nitrogen (N), phosphorus (P), and potassium (K) were 4.2 t ha-1 , 3.0 t ha-1 , and 4.3 t ha-1 , respectively. The average relative yields (RYs) of lychee for N, P, and K were 0.73, 0.80, and 0.77, respectively. The mean values of soil indigenous nutrient supply for N, P, and K were 52.4 kg ha-1 , 5.7 kg ha-1 , and 44.2 kg ha-1 , respectively. The average agronomic efficiencies (AEs) were 15.8 kg N kg-1 , 62.8 kg P kg-1 , and 18.2 kg K kg-1 , respectively. The YR and AE of N, P and K were well fitted by quadratic equations. Significant negative exponential correlations were detected between the YR and the indigenous nutrient supply. A significant negative linear correlation was detected between YR and RY in lychee production. In validation experiments, the NE approach outperformed farmers' practices in terms of yield, output-input ratio, the net return, and N use efficiency. The NE system is a feasible approach to making fertilization recommendations for small-scale lychee farmers without the need for testing.

Optimizing biochar use requires understanding its effects on soil microbes and crop yield, yet the role of soil texture remains unclear. In a two-year field experiment with a winter wheat–summer maize rotation on sandy and fluvo-aquic soils, biochar was applied at rates of 0, 10, and 20 t ha⁻¹. In sandy soil, biochar increased maize yield by 9.8% in the first year and by 13.1% in the second year, and wheat yield by 8.0% in the second year. In fluvo-aquic soil, only the 10 t ha⁻¹ rate increased maize yield by 9.7% in the second year. Biochar altered soil properties and enzyme activities in both soils, but microbial community responses varied with soil type, and soil type exerted a stronger influence than biochar application rate. In fluvo-aquic soil, the highest biochar application rate (20 t ha⁻¹) enhanced bacterial richness and diversity with a changed community structure, increasing Acidobacteria and Chloroflexi while decreasing Proteobacteria, whereas no such effects were observed in sandy soil. These community shifts were correlated with available potassium, urease, and sucrase, factors themselves affected by biochar. Fungal diversity and community structure were unaffected in either soil. Biochar increased yields through direct physicochemical improvements in sandy soil, whereas in fluvo-aquic soil it acted via combined physicochemical and microbial effects. Overall, the effects after two years of biochar on soil microorganisms and crop yield strongly depend on soil texture, mediated by complex interactions among soil properties. Given that the study involved a single biochar type and two soil types, further research across broader conditions is needed to verify the generality of these conclusions.