The aim of this study was to verify the applicability of the critical nitrogen concentration dilution curve (Nc) of wheat grown under different irrigation conditions in the field, and discuss the feasibility of using the N nutrition index (NNI) to optimize N fertilizer application. The high-yield, medium-protein wheat varieties Zhoumai 27 and Zhoumai 22 were used in field experiments in two different locations (Zhengzhou and Shangshui) in Huang-Huai, China. Plants were grown under rainfed and irrigation conditions, with five N application rates. Nc models of the leaves, stems, and whole plant were constructed, followed by establishment of an NNI model and accumulative N deficit model (N_and). As previous research reported, our results also showed that the critical N concentration and biomass formed a power function relationship (N = aDW^−b). When the biomass was the same, the critical N concentration was higher under irrigation than rainfed treatment. Meanwhile, the fitting accuracy (R²) of the Nc model was also higher under irrigation than rainfed treatment in both sites, and was higher in the stems and whole plant. The NNI calculated using the Nc model increased with increasing N application, reflecting N deficiency. Moreover, there was a significant negative linear correlation between NNI and N_and, and both indices could be uniformly modeled between locations and water treatments. The accuracy of the N_and model was highest in the whole plant, followed by the leaves and stems. The models constructed in this paper provide a theoretical basis for accurate management of N fertilizer application in wheat production.

Rational regulation of phosphorus (P) use in the soil–rhizosphere–plant system is challenging in the development of sustainable, intensive, and healthy agriculture. Rational maize (Zea mays L.) based intercropping with legumes/oilseed rape across six experimental sites from 2008 to 2017 proved advantageous over monoculture in terms of both maize biomass production and P uptake. The partial land equivalent ratio (PLER) for P uptake by intercropped maize averaged from 0.58 to 0.92, which was significantly higher than that for biomass production (0.51–0.78), indicating that the advantage of P acquisition by intercropped maize was superior to that of biomass accumulation. It was the excessive accumulation of P in intercropped maize compared to monoculture, especially higher P concentrations in grains that led to the superior P acquisition advantage and luxury absorption of P. P concentrations in maize grains were significantly increased from 1.89–2.91 mg kg⁻¹ in monoculture to 2.09–3.65 mg kg⁻¹, in intercropping, by 8.3%–25.5%. The plant internal P use efficiency of maize was significantly decreased from the initial 411.7–775.7 kg kg⁻¹ in monoculture to 345.7–710.4 kg kg⁻¹ in intercropping by 4.9%–16.0%, and 100 kg maize grain P quantities were significantly increased from 0.25–0.46 kg to 0.27–0.54 kg by 7.0%–17.4%. Rational fertilizer P input maximized maize yields and P use without decreasing the interspecific ecological advantages and harvest indexes of grain yields and P. These findings promoted better understanding of P allocation status within maize plants, and yield and P acquisition advantages through the exploitation of the biological potential of plants for the efficient utilization of P resources in diverse species combinations.

The intercropping of maize (Zea mays L.) and peanuts (Arachis hypogaea L.) (M||P) significantly enhances crop yield. In a long-term M||P field experiment with two P fertilizer levels, we examined how long-term M||P affects topsoil aggregate fractions and stability, organic carbon (SOC), available phosphorus (AP), and total phosphorus (TP) in each aggregate fraction, along with crop yields. Compared to their respective monocultures, long-term M||P substantially increased the proportion of topsoil mechanical macroaggregates (7.6–16.3%) and water-stable macroaggregates (>1 mm) (13.8–36.1%), while reducing the unstable aggregate index (E_LT) and the percentage of aggregation destruction (PAD). M||P significantly boosted the concentration (12.9–39.9%) and contribution rate (4.1–47.9%) of SOC in macroaggregates compared to single crops. Moreover, the concentration of TP in macroaggregates (>1 mm) and AP in each aggregate fraction of M||P exceeded that of the respective single crops (p < 0.05). Furthermore, M||P significantly increased the Ca₂-P, Ca₈-P, Al-P, and Fe-P concentrations of intercropped maize (IM) and the Ca₈-P, O-P, and Ca₁₀-P concentrations of intercropped peanuts (IP). The land equivalent ratio (LER) of M||P was higher than one, and M||P stubble improved the yield of subsequent winter wheat (Triticum aestivum L.) compared with sole-crop maize stubble. P application augmented the concentration of SOC, TP, and AP in macroaggregates, resulting in improved crop yields. In conclusion, our findings suggest that long-term M||P combined with P application sustains farmland productivity in the North China Plain by increasing SOC and macroaggregate fractions, improving aggregate stability, and enhancing soil P availability.

Finding field management techniques that increase crop output while protecting soil sustainability is essential for maintaining a long-term food supply in a changing environment. However, comprehensive evaluation of the effects of nitrogen (N) reduction combined with organic fertilizer on grain yield, N use efficiency (NUE), water use efficiency (WUE), and soil organic carbon (SOC) and total N (TN) contents of winter wheat–summer maize double cropping systems in drought-prone areas remains limited. Therefore, a 3-year field experiment (2018–2021) was conducted in a winter wheat–summer maize double cropping system with five treatments: no N fertilizer (CK), conventional farmer fertilization (CF), recommended fertilization (R), organic N substitution of 20% of the recommended synthetic N (R₂₀), and organic N substitution of 40% of the recommended synthetic N (R₄₀). When results were averaged from 2018 to 2021, R₂₀ had the highest annual grain yield, which increased by 42.15%, 7.69%, 7.58%, and 12.50% compared with CK, CF, R, and R₄₀, respectively. Compared with CF, R₂₀ increased winter wheat and summer maize NAE, NPFP, NUE, and WUE. In addition, the soil organic carbon content of R₂₀ and R₄₀ treatment increased with the increase in years. In conclusion, R₂₀ was considered ideal for improving crop yield, promoting soil fertility, and increasing the fertilizer utilization rate in a semiarid winter wheat–summer maize rotation.

Intercropping and phosphorus application are effective ways to increase crop yield and improve cultivated land quality. This study took the soil under the maize-peanut intercropping system which has been planted for 12 years as the research object, the physical, chemical, and electrochemical properties of soil, and crop yield under different planting patterns [sole-crop maize (SM), sole-crop peanut (SP), and maize-peanut intercropping (M/P)] and phosphorus application rates [P application (180 kg P₂O₅ ha⁻¹) and no P application (0 kg P₂O₅ ha⁻¹)] were studied. The results showed that intercropping increased soil aggregate stability, clay content, and gas phase ratio, P application further optimized the soil physical properties. At the same time, intercropping decreased soil pH and EC, increased soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents. P application increased soil pH, SOC, TN, TP, and EC. Compared with monoculture, intercropping increased the surface charge number (SCN) by 19.98%, specific surface area (SSA) by 44.34%, surface charge density (σ₀) by 38.08, electric field strength (E₀) by 38.22, and Zeta potential by 46.85%. P application further increased the SCN by 20.75%, SSA by 23.43%, σ₀ by 67.82%, E₀ by 67.13%, and Zeta potential by 15.51%. Maize-peanut intercropping increased the total crop yield of the intercropping system, the application of phosphate fertilizer further increased the yield of maize and peanut. The aggregate stability and nitrogen were significantly positively correlated with crop yield, and the carbon, phosphorus, and electrochemical properties were extremely significantly positively correlated with crop yield.