Rotational cover cropping is a key practice in conservation agriculture. To investigate the effects of maize-crop rotation with cover crops combined with nitrogen management on maize yield, nitrogen use efficiency (NUE), and related traits, a field experiment was conducted from 2023 to 2025. The experiment employed a split-plot design. The main plots consisted of three cropping systems: continuous maize (Fumin 985’) monoculture (CK), maize rotated with rapeseed (CC-Ra), and maize rotated with rye (CC-Ry). The subplots comprised five nitrogen (N) fertilizer application rates (0, 75, 150, 225, and 300 kg ha⁻¹) respectively. Compared to CK, CC-Ra and CC-Ry increased average maize grain yield by 5.93% and 12.89%, and NUE by 8.09% and 2.89%, respectively. At the silking stage, these treatments increased average DM by 6.45% and 16.55%, respectively, and by 5.75% and 15.01% at the maturity stage. The maximum LAI was enhanced by an average of 16.24% and 26.82%, while the net photosynthetic rate (Pn) of the ear leaf increased by 12.29% and 26.32%, respectively. In contrast, the leaf net assimilation rate (NAR) decreased by an average of 19.98% and 18.01%. While higher N application boosted yield, it sharply reduced NUE. Notably, yields under rotations at 225 kg N ha⁻¹ matched the yield of continuous maize at 300 kg N ha⁻¹. This suggests that the inclusion of cover crops can substitute for a portion of nitrogen fertilizer input while maintaining stable maize yield. Principal component analysis fundamentally clarified that maize rotational cover cropping combined with nitrogen fertilizer management significantly promotes yield. While cover crops increase maize yield, they also facilitate nitrogen accumulation and enhance NUE, albeit at the expense of leaf net assimilation rate. Therefore, balancing the source–sink characteristics of the maize population is necessary to avoid the loss of advantages conferred by rotational cover cropping. This study holds significant implications for incorporating cover crops into maize production systems.

Extracellular enzyme stoichiometry is a key indicator for assessing nutrient limitation experienced by soil microorganisms. Yet, the characteristics of enzyme-inferred microbial nutrient limitation in rhizosphere soil under the combined agricultural practices of intercropping and straw retention remain unclear. Here, we conducted a field experiment in the black soil region of Northeast China to quantify the effects of intercropping and straw retention on soil nutrients, microbial biomass, extracellular enzyme activities, and their C:N:P stoichiometry in the rhizosphere of maize and peanut. Our results showed that compared with sole cropping, intercropping increased soil organic carbon (SOC) by 6.21–13.57%, total nitrogen (TN) by 8.57–12.49%, and total phosphorus (TP) by 12.01–40.29% in the rhizosphere. The vector analysis revealed an average vector length (VL) of 1.68 and 1.57 for extracellular enzymes in the rhizosphere soil of maize and peanut, with a vector angle (VA) of 37.80° and 34.67°, respectively. These values suggest that soil microorganisms in the rhizosphere of both crops experienced C limitation, and that the degree of enzyme-inferred N limitation was modulated by microbial C acquisition strategies, with a dynamic trade-off between the two. This N limitation was more pronounced in the peanut rhizosphere. Notably, the combined treatment of intercropping and full straw retention increased the VA of peanut by 5.38%, corresponding to a partial alleviation of enzyme-inferred N limitation in the rhizosphere soil. The extracellular enzyme C:N:P stoichiometry in the rhizosphere soil of maize and peanut was 1.33:1.29:1.00 and 0.89:1.29:1.00, respectively. Microbial biomass nitrogen (MBN) was the primary factor affecting enzyme-inferred microbial nutrient limitation (explaining 54.6% of variation). The extracellular enzyme stoichiometric characteristics of rhizosphere soil differed significantly between the two crops. Intercropping had a stronger impact on rhizosphere microbial nutrient limitation than straw retention, and their synergistic effect was associated with a partial alleviation of rhizosphere enzyme-inferred N limitation by enhancing extracellular enzyme activity. These findings demonstrate that integrated intercropping and straw retention can support sustainable soil management in black soil agroecosystems.