We conducted pot experiments to assess the bioavailability of cadmium (Cd) in contaminated rhizosphere soil and accumulation in rice organs in response to nitrogen (N) supply ((NH₄)₂SO₄, NH₄NO₃, NH₄Cl). The results showed that the concentration of bioavailable Cd in rice rhizosphere soil was (NH₄)₂SO₄ treatment > NH₄Cl treatment > NH₄NO₃ treatment at the same level of N application and growth period; the Cd concentration in rice roots was (NH₄)₂SO₄ treatment > NH₄NO₃ treatment > NH₄Cl treatment; and the Cd concentration in rice straw was NH₄NO₃ treatment > NH₄Cl. The Cd concentration in rice roots, straws, and seeds at the maturity stage was (NH₄)₂SO₄ treatment > NH₄Cl treatment. With the same N fertilizer, excessive N promoted Cd accumulation in rice at later growth stages. This suggested that sulfate (SO₄²⁻) influenced Cd concentration in rice. NH₄Cl application maintained a low Cd level in different rice organs with the same N level. This confirmed that NH₄Cl is a safe N source for rice planting in polymetallic sulfide mining areas. The study concludes that appropriate NH₄Cl levels for Cd-contaminated paddy soil with high-S-content could obtain rice grains with Cd concentrations below the food safety standards (0.2 or 0.4 mg·kg⁻¹).

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.

Here, we established abundance and deficiency indices of soil nutrients and fertilization to generate a reference for the optimum fertilization dosage of the main vegetable crops in southern China under current production conditions. We consolidated 3414 field datasets about the main vegetable crops (leafy vegetables, gourds, legumes) in this region between 2010 and 2013. The nutrient abundance and deficiency index method was used to separate soil alkali-hydrolyzable nitrogen, available phosphorus, and available potassium levels into five groups based on relative vegetable yields (range: 50%–95%). Recommended fertilizer dosages were determined by obtaining values for nitrogen, phosphorus, and potassium by fitting optimum dosage against available nutrient content. Required fertilization levels were dependent on soil conditions and crop type. Comparison of the study results showed that available phosphorus and available potassium had significantly improved, whereas alkali-hydrolysable nitrogen in each level was similar.

The influence of Shewanella oneidensis MR-1 on the transformation of iron oxides and phosphorus in a red soil | Weimin Yu, Rongping Wang, Rongyun Linghu, Jiawei Liang, Qiqi Hu, Yuling Yao | Agricultural Journals