Nitrogen (N) is an essential macronutrient for plant growth and excessive application rates can decrease crop yield and increase N loss into the environment. Field experiments were carried out to understand the effects of N fertilizers on N utilization, crop yield and net income in wheat and maize rotation system of the North China Plain (NCP). Compared to farmers’ N rate (FN), the yield of wheat and maize in reduction N rate by 21-24% based on FN (RN) was improved by 451 kg ha-1, N uptakes improved by 17 kg ha-1 and net income increased by 1671 CNY ha-1, while apparent N loss was reduced by 156 kg ha-1. The controlled-release fertilizer with a 20% reduction of RN (CRF80%), a 20% reduction of RN together with dicyandiamide (RN80%+DCD) and a 20% reduction of RN added with nano-carbon (RN80%+NC) all resulted in an improvement in crop yield and decreased the apparent N losses compared to RN. Contrasted with RN80%+NC, the total crop yield in RN80%+DCD improved by 1185 kg ha-1, N uptake enhanced by 9 kg ha-1 and net income increased by 3929 CNY ha-1, while apparent N loss was similar. Therefore, a 37-39% overall decrease in N rate compared to farmers plus the nitrification inhibitor, DCD, was effective N control measure that increased crop yields, enhanced N efficiencies, and improved economic benefits, while mitigating apparent N loss. There is considerable scope for improved N use effieincy in the intensive wheat -maize rotation of the NCP.

The appropriate nitrogen (N) fertilizer regulator could increase N utilization of crops and reduce N losses in the North China Plain. We investigated the effects of reduced inorganic-N rate combined with an organic fertilizer on nitrous oxide (N₂O) emissions in winter wheat and summer maize rotation system. Simultaneously studied the effect of different treatments on N use efficiency (NUE), N balance and net income. After reducing the amount of nitrogen fertilizer in the wheat-corn rotation system, the results showed that the cumulative emission of soil N₂O from the RN40% + HOM [40% of RN (recommended inorganic-N rate) with homemade organic matter] treatment was 41.0% lower than that of the RN treatment. In addition, the N production efficiency, agronomic efficiency, and apparent utilization were significantly increased by 50.2%, 72.4% and 19.5% than RN, respectively. The use of RN40% + HOM resulted in 22.0 and 30.1% lower soil N residual and N losses as compared with RN. After adding organic substances, soil N₂O cumulative emission of RN40% + HOM treatment decreased by 20.9% than that of the HAN (zinc and humic acid urea at the same inorganic-N rate of RN) treatment. The N production efficiency, N agronomic efficiency and NUE of RN40% + HOM treatment were 36.6%, 40.9% and 15.3% higher than HAN’s. Moreover, soil residual and apparent loss N were 23.3% and 18.0% less than HAN’s. The RN40% + HOM treatment appears to be the most effective as a fertilizer control method where it reduced N fertilizer input and its loss to the environment and provided the highest grain yield.

The application of straw-degrading microbes (SDMs) with straw returned to the field is an effective measure to improve soil quality, increase yield, and maintain soil microorganisms. However, the utilization of SDMs in winter in north China is limited by the poor effects at low temperatures. This study investigated the effects of a new compound SDM, including a novel low-temperature fungus Pseudogymnoascus sp. SDF-LT, on winter wheat yield, soil improvement, and soil microbial diversity. A 2-year field experiment was conducted in two different soil textures of wheat–maize rotation fields with full corn straw return and application of SDMs at an amount of 67.5 kg hm⁻². After 2 years of continuous application of SDMs, the winter wheat yield increased significantly, reaching 9419.40 kg hm⁻² in Ningjin (NJSDM) and 9107.25 kg hm⁻² in Mancheng (MCSDM). The soil properties have been significantly improved compared with the single straw return group, especially the sandy loam soil, whose quality is relatively low. The analysis of soil microbial diversity showed that SDMs significantly reduced the Chao1, Shannon, Simpson, and observed species of the sandy loam soil in the MCSDM group. The Simpson and Shannon indexes of fungi diversity in the two experimental sites were significantly increased by SDMs. The negative correlation of fungi increased from 47.1 to 48.85% in the SDM groups. The soil-dominant microbes changed in the SDM groups, in which the interactions between microbes were enhanced. These results suggested that the SDMs changed the the soil microbial community structure and its diversity and complexity, which is beneficial for crop growth. Our study provided sufficient evidence for the utilization of low-temperature SDMs with straw return in cold winter, which plays a role in soil improvement, especially for low-quality soils, to increase crop yield.

Over-fertilization could lead to nitrogen (N) losses and environmental risks, and the appropriate nitrogen fertilizer could reduce the nitrous oxide (N₂O) emission and increase the N utilization of crops in the North China Plain. We investigated the effects of rationally reduced N fertilizer input and nitrapyrin (CP) application on N₂O dynamic emission, soil N balance, yield, N utilization and net income during the whole wheat season. Five fertilization treatments included zero N (CK), farmers’ traditional N rate (FN), recommended N rate (RN), the 20% reduction of RN (80%RN) and the 20% reduction of RN added with CP (80%RN+CP). The N₂O emission fluxes from seedling stage to greening stage contributed to 51.1%-74.2% during the whole wheat growth stages. Moreover, the first peak of N₂O emission was observed within half a month after N basal fertilizer, irrigation, and sowing, which was two times higher than the other peaks occurred after N top-dressing and irrigation. The cumulative N₂O emission and N₂O emission factor were significantly declined by 27.3%-43.4% and 8.9%-51.1% with 80%RN and 80%RN+CP as compared to FN, respectively. Grain yield, agronomic N use efficiency, apparent N use efficiency and N production efficiency with 80%RN+CP were increased by 1.74%-10.83%, 0.9–8.91 kg kg⁻¹, 1.9%-27.5% and 1.22–22.79 kg kg⁻¹ than other N treatments, respectively. Moreover, 80%RN+CP also decreased N loss by 7.88–55.62 kg ha⁻¹ as compared to FN and RN, which resulted in less soil NO₃⁻ retention. Consequently, the application of nitrapyrin with 20% reduction of N rate should be recommended to increase winter wheat economic benefits and mitigate environmental pollution in North China Plain.

Biochar amendment has been widely recognized for its potential to promote soil carbon sequestration and improve crop productivity; however, the microbial mechanisms underlying carbon sequestration at varying biochar application rates remain insufficiently understood. In this study, a field experiment was conducted in a typical fluvo-aquic soil region of the North China Plain under a maize–wheat rotation, with one-time biochar application at four levels: CK (0 t ha⁻¹), B5 (5 t ha⁻¹), B10 (10 t ha⁻¹), and B20 (20 t ha⁻¹). The effects of these treatments on soil physicochemical properties, organic carbon fractions, microbial community structure, and enzyme activities were systematically examined. The results showed that soil total nitrogen (TN) and pH increased consistently with higher biochar application rates, reaching maximum values under B20 treatment, where TN and pH rose by 35.56% and 7.00% relative to CK, respectively. In contrast, the contents of NH₄⁺-N, available phosphorus (AP), and available potassium were mostly enhanced under B5 during the maize season, while in the wheat season, NH₄⁺-N peaked under B10 and AP peaked under B5. Biochar addition significantly increased soil organic carbon fractions and the carbon pool management index (CMI). In the maize season, soil organic carbon (SOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and CMI under B20 rose by 55.99%, 39.67%, 79.69% and 180.54% over CK, respectively, whereas dissolved organic carbon (DOC) peaked under B5. Throughout the wheat season, SOC, MBC, and POC contents under B20 were 53.70%, 64.31% and 147.81% higher than CK, while DOC peaked under B5 (+56.98%). Soil enzyme activities, including catalase, urease, invertase and alkaline phosphatase, were strongly stimulated by biochar, with B20 increasing their activities by 4.49–18.18%, 3.19–19.77%, 6.14–26.14% and 12.25–33.19%, respectively. Biochar also reshaped microbial community structure: the during maize season, it reduced the relative abundance of Glomeromycetes (65.31%) and Oligohymenophorea (51.64%) while enhancing Deltaproteobacteria (46.15%) and Gammaproteobacteria (29.03%); during wheat season; it enhanced Eurotiomycetes (85.77%) and Dothideomycetes (16.28%) but suppressed Deinococci (74.08%) and Alphaproteobacteria (4.39%). Pathway analysis further indicated that biochar amendments indirectly increased SOC fractions and CMI by simultaneously altering nutrient availability, regulating microbial community structure, and stimulating soil enzyme activities. Collectively, these findings highlight that the effects of biochar are dosage-specific: moderate rates (e.g., 5 t ha ⁻¹) are more suitable for the short-term improvement of soil fertility, while higher rates (e.g., 20 t ha⁻¹) are more effective for long-term carbon sequestration; depending on the objective, biochar application can thus substantially modify soil physicochemical and biological processes to promote agroecosystem sustainability in the North China Plain.

High-profile nutrient accumulation has caused low nutrient use efficiency and environmental pollution. A total of 140 points in farmers’ wheat fields were investigated and sampled under a typical winter wheat and summer maize rotation system in the Huang-huai-hai Plain of China (HPC). The average wheat yield in the high-yield field is more than 10% relative to the mid-low-yield areas based on historical data. The results showed in the high-yield wheat field the effective spike number was the main yield component, followed by 1000-grain weight. Uptake contents and ratios of N, P₂O₅ and K₂O in the whole wheat plant were also examined. Along the soil depth, organic matter (OM), alkali-hydrolyzable N (AN), available P (AP) and available K (AK) concentration gradually decreased. Soil critical values of AN, AP and AK in the 0–20 cm depth needed to achieve the maximum grain yield were 85.9, 17.7 and 114.2 mg kg⁻¹ calculated by the significant linear-plus-plateau model between wheat grain yield and soil nutrient concentration at harvest, respectively. These results indicated that the rational application of fertilizer based on the soil nutrient supply capacity and residual nutrients in root zone and optimum planting density are key determinants of grain production in the HPC.