Rice husk and cotton straw were used to produce biochar under 300, 400, 500, 600, and 700 °C pyrolysis conditions, and the physicochemical properties of the obtained biochar samples were characterised. The effects of various adsorbent amounts, initial pH, and adsorption time on the Cd²⁺ adsorption performance were studied. The results showed that, at increasing pyrolysis temperatures, the biochar yield decreased, the ash content increased, the pH transitioned from acidic/neutral to basic/strongly basic, the biochar aromaticity gradually increased, and the biochar structure became more stable. In contrast, the hydrophilicity and polarity decreased, the specific surface area increased, and the number of oxygen-containing functional groups decreased. All these factors resulted in differences in the Cd²⁺ adsorption by the biochar samples. With increasing adsorbent content, the rate of Cd²⁺ adsorbed on the biochar gradually increased. The adsorption performance was optimal when the initial solution pH of the rice-husk and cotton-straw biochar samples was 5 and 6, respectively. The shortest time to achieve equilibrium was 30 min for rice-husk biochar, and 20 min for cotton-straw biochar. The Cd²⁺ adsorption data for both types of biochar were very well fitted with a pseudo-second-order kinetic model. Ion exchange and cation–π interactions may be the main factors influencing the Cd²⁺ adsorption by biochar. At the same time, the large specific surface area of biochar also plays a role in the Cd²⁺ adsorption.

Recovery efficiency of nitrogen fertilizers has always been an important issue, especially for N fertilizer recommendation rate in cropping systems. Based on the equilibrium of N in the soil–plant system, apparent accumulated N fertilizer recovery (NRE_ac) was determined for long-term (15-years) experiments in wheat (Triticum aestivum L.) and maize (Zea mays L.) rotations at five field sites with various soils and climate characteristics in China. The result showed that the frequency of cropping and the content of soil clay affected NRE_ac positively and negatively, respectively. In the absence of nutrient deficiencies and other soil constraints (from NPK (nitrogen, phosphorus and potassium) in S2-CP (site2-Changping) in Beijing, S3-ZZ (site3-Zhengzhou) in Henan province and S4-YL (site4-Yangling) in Shaanxi province), NRE_ac had a narrow range from 70% to 78% with the highest average of 75% in wheat and maize cropping system. Meanwhile, the value 75% of NER_ac is a rational value proved by 3414 experiments. Additionally, the nitrate-N approach suggested that nitrate-N could be utilized by subsequent crops, the amount of which is calculated by the equation −1.23 × [(NO₃⁻-N) − 87]. Furthermore, another simpler and feasible method was proposed to maintain basic soil fertility while achieving a rational grain yield and maintaining a safe environmental upper threshold of nitrate. The present study provided a suit of methods for N fertilizer recommendations for the optimization of N applications in wheat and maize cropping system in China.

Soil aggregation, a critical component of soil structure, is significantly influenced by soil moisture content, which can vary substantially across different field conditions. The objective of this study was to evaluate the impact of soil relative water content (SRWC) on the performance and sensitivity of soil aggregate size distribution (DOSA) assessments. We conducted a comprehensive analysis across a range of SRWC levels and observed a consistently high recovery rate of sieving (exceeding 99.22%), indicating a robust methodology. The relative standard deviation (RSD) of DOSA was minimal, highlighting the high precision of sieving outcomes, particularly up to an SRWC of 40%. Cluster analysis, based on soil properties, identified six distinct soil groups, each demonstrating a significant correlation between the characteristic values of DOSA and SRWC, with determination coefficients (R²) above 0.717. This finding underscores the sensitivity of aggregate distribution to variations in moisture levels. However, the fitting curves varied among clusters at the same site, with the exception of clusters 5 and 6 at the Jinliuhuan Agricultural Sci-Tech Park (JLH), reflecting the intricate nature of soil–moisture interactions. Our results emphasize the necessity of sieving soil aggregates under controlled field moisture conditions to ensure reliable DOSA measurements. This research provides valuable insights into the dynamics of soil aggregation and its response to different moisture regimes, offering practical implications for enhancing sustainable agricultural practices. This study provides a comprehensive analysis of the impact of soil relative water content (SRWC) on soil aggregate size distribution (DOSA), revealing the high recovery rate and precision of sieving under various moisture conditions. The significant correlation between DOSA and SRWC, along with the varied responses across soil clusters, highlights the complex interplay between soil moisture and aggregate stability. These findings are crucial for optimizing soil aggregate assessments and sustainable agricultural practices.

Prediction of accumulation of available phosphorus (P) in paddy soils is crucial for the best management of P fertilizers. Based on the long-term double-rice rotation systems, a predictive model for accumulation rates of Olsen P in paddy soils with chemical fertilization was developed. In paddy soils with more than 40 kg applied P ha⁻¹, the accumulation of Olsen P in the soils could occur. With the target rice yield of 10 tons ha⁻¹ per year, the increases in Olsen P in paddy soils were estimated by the model as 0.7, 2.2, and 3.8 mg kg⁻¹ when P application rates are 40, 60, and 80 kg P ha⁻¹, respectively. The accumulation rate of Olsen P was relatively high in paddy soils. The predictive model can be used to predict accurately the concentrations of Olsen P in paddy soils based on initial Olsen P, P application rate, and crop yield and to optimize P fertilization for rice crop production and environmental protection.