Green manure application presents a valuable strategy for enhancing soil fertility and promoting ecological sustainability. By leveraging green manures for effective nitrogen management in agricultural fields can significantly reduce the dependency of primary crops on chemical nitrogen fertilizers, thereby fostering resource efficiency. This review examines the current advancements in the green manure industry, focusing on the modulation of nitrogen transformation in soil and how crops absorb and utilize nitrogen after green manure application. Initially, the influence of green manure on soil nitrogen transformation is delineated, covering processes such as soil nitrogen immobilization, and mineralization, and losses including NH₃, N₂O, and NO₃⁻-N leaching. The review then delves into the effects of green manure on the composition and function of soil microbial communities, highlighting their role in nitrogen transformation. It emphasizes the available nitrogen content in the soil, this article discussing nitrogen uptake and utilization by plants, including aspects such as nitrogen translocation, distribution, the root system, and the rhizosphere environment of primary crops. This provides insights into the mechanisms that enhance nitrogen uptake and utilization when green manures are reintroduced into fields. Finally, the review anticipates future research directions in modulating soil nitrogen dynamics and crop nitrogen uptake through green manure application, aiming to advance research and the development of the green manure sector.

Nitrogen (N) fixation is essential in the development of sustainable agriculture, but nodulation of legumes is usually inhibited by N fertilization. In this study, we evaluated the increased density of intercropped maize (Zea mays L.) as a means to alleviate the inhibitory effect of soil mineral N on intercropped pea (Pisum sativum L.) and improve system performance. A field experiment was conducted in the Hexi Corridor region of northwestern China from 2012 to 2014. The experiment consisted of monoculture pea, monoculture maize, and a pea/maize strip-intercropping system. Two levels of N fertilization were evaluated in both cropping systems during the co-growth period of intercropping, i.e., 0 kg N ha⁻¹ (N0) and 135 kg N ha⁻¹ (N1), and three maize densities were evaluated with both levels of N fertilization in the intercropping system, i.e., 45,000 plants ha⁻¹ (D1), 52,500 plants ha⁻¹ (D2), and 60,000 plants ha⁻¹ (D3). The application of N reduced the number of nodules of intercropped pea by 135% at D1 and by 9% at D2 compared to no application of N, in all the years examined. The alleviation of the inhibitory effect of soil mineral N on the nodulation of intercropped pea (C_is) was calculated as the percentage increase in nodulation with intercropping relative to monoculture for a given level of N fertilization. With the application of N, C_is was improved by increased intercropped maize density (D3 > D2 > D1) at all stages. The internal efficiency of nitrogen (IEN) of pea was improved with intercropping and, on average, was 19% and 12% greater at D3 than at D1 and D2, respectively. These results demonstrate that increased maize density can alleviate the inhibitory effect of soil N on the nodulation of pea and sustain the productivity of maize/pea intercropping while reducing N fertilizer requirements in arid regions.

Sustainable agricultural intensification requires innovative approaches to simultaneously enhance productivity and mitigate environmental impacts—a challenge critical to global food security and climate change mitigation. The traditional fertilization system, with a single application of nitrogen fertilizer, while effective for crop yields, often leads to soil organic carbon (SOC) depletion, whereas green manure systems offer a dual benefit of nitrogen supply and SOC sequestration potential. However, the mechanisms by which green manure substitution enhances soil carbon sequestration (SCS) remain systematically underexplored in comparison to chemical fertilization. This review systematically examines (1) the mechanisms underlying SOC sequestration, (2) SOC losses associated with traditional fertilization practices, and (3) the theoretical foundation and practical applications of green manure as a nitrogen fertilizer substitute. We provide an in-depth analysis of the mechanisms through which green manure substitution drives SCS. Furthermore, we identify three critical areas for future investigation: (i) optimization of green manure management strategies to enhance SCS efficiency; (ii) comprehensive assessment of green manure’s ecological benefits through long-term, multi-scale studies; and (iii) evaluation of green manure’s climate change adaptation capacity and carbon sequestration potential across diverse climatic scenarios. These findings fundamentally advance our understanding of green manure’s role in sustainable agriculture by establishing its dual function as both a nitrogen source and carbon sequestration driver. In addition, these insights have immediate relevance for agricultural policy and practice, particularly in regions where soil health and carbon storage are prioritized alongside crop yield.

Above- and below-ground interactions play a crucial role in achieving higher yields in intercropping systems. Nonetheless, it remains unclear how these interactions impact intercropping crop growth and regulate interspecific relationships. This study aimed to quantify the impact of above- and below-ground interactions on crop yield by determining the dynamics of dry matter accumulation, photosynthetically active radiation (PAR) transmittance, and leaf area index (LAI) in intercropped wheat and maize. Three below-ground intensities were set for an intercropping system: no root separation (CI: complete interaction below ground), 48 μm nylon mesh separation (PI: partial interaction below ground), and 0.12 mm plastic sheet separation (NI: no interaction below ground). Two densities were set for maize: low (45,000 plants hm⁻²) and high (52,500 plants hm⁻²). At the same time, corresponding monoculture treatments were established. The grain yields in the CI and PI treatments were, on average, 23.7% and 13.7% higher than those in the NI treatment at high and low maize densities, respectively. Additionally, the grain yield for high density was 12.3% higher than that of low density in the CI treatment. The dry matter accumulation of intercropped wheat under the CI and PI treatments was, on average, 9.1%, 14.5%, and 9.0% higher than that in the NI treatment at the flowering, filling, and maturity stages, respectively. The dry matter accumulation of intercropped maize at the blister, milk, and physiological maturity stages increased by 41.4%, 32.1%, and 27.8%, respectively, under the CI treatment compared to the NI treatment. The PAR transmittance and LAI of maize at the V6 stage were significantly increased by increasing the intensity of below-ground interactions. This study showed that complete below-ground interaction contributed to a significant increase in the competitiveness of intercropped wheat with respect to maize (A_wm) under the high-density maize treatment, especially at the filling stage of wheat. Moreover, the CI treatment enhanced the recovery effects of maize (R_m) after wheat harvesting. Increasing the intensity of below-ground interactions can significantly enhance the A_wm and R_m in intercropping systems, favoring the accumulation of crop dry matter mass and light energy utilization to increase system yields.