The full implementation of an environmental protection tax is an important measure to realize the goal of emission reduction and promote the comprehensive green transformation of economic and social development. In this paper, we take China’s environmental protection tax reform as a “quasi-natural experiment”, based on the data of A-share listed companies from 2013 to 2022, and utilize a differences-in-differences (DID) model to assess the impact of this policy on the performance of heavily polluting firms. The study finds that the environmental protection tax reform improves the performance of heavily polluting firms by 1.09% on average, which still holds after a series of robustness tests. Mechanistic analysis shows that environmental protection tax reform improves firm performance by accelerating firms’ digital transformation and increasing strategic green innovation activities. Heterogeneity analysis shows that the improvement of environmental protection tax reform on the performance of heavily polluting firms will be more obvious in large-scale firms and tax burden-raising regions. This paper provides micro-empirical evidence to further promote the improvement and implementation of the environmental protection tax system.

Strategic management of nitrogen fertilizers can not only mitigate agricultural nitrogen pollution but also significantly enhance crop yield and nitrogen use efficiency. This study was designed to determine the optimal nitrogen fertilizer management strategy for the Yellow River irrigation area. Leveraging two years of field data related to soil water nitrogen and summer maize growth indices, parameters for the Root Zone Water Quality Model 2 (RZWQM2) were calibrated and validated. Subsequently, various scenarios were generated to simulate the impacts of different nitrogen application rates and basal chasing ratios on summer maize yield, nitrogen agronomic efficiency, nitrogen physiological efficiency, and nitrogen apparent recovery rate. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method was employed for a comprehensive evaluation. RZWQM2 can effectively simulate the dynamic changes in soil moisture and nitrogen in the Yellow River irrigation area, and the results indicated that the mean relative error (MRE) between the simulated and observed values varied from 5.77% to 14.09%, and 4.36% to 33.01%, while the root mean square error (RMSE) ranged from 0.016 to 0.037 cm³/cm³, and 0.111 to 1.995 mg/kg. The normalized root mean square error (NRMSE) varied between 6.20% to 14.42% and 5.24% to 17.84%, respectively. The results validate the model’s effectiveness in simulating summer maize yields and nitrogen metrics under varying nitrogen fertilizer management practices. A nitrogen application rate of 180–200 kg/hm² (expressed in terms of pure nitrogen) in the Yellow River irrigation area could adequately meet the requirements for summer maize production. The recommended nitrogen fertilizer management strategy in the Yellow River irrigation area involves applying 200 kg/hm² of nitrogen in a 1:2:1 ratio during the sowing, trumpeting, and anthesis stages.

The transplanted cotton–wheat rotation enables dual cropping but alters root system architecture, typically suppressing taproot growth and promoting shallow lateral and fibrous roots, with unclear implications for irrigation response and water use efficiency (WUE). Field experiments were conducted in 2021 and 2022 to investigate root growth, spatial distribution, and water uptake sources, using a minirhizotron system and stable hydrogen and oxygen isotopes. The study examined the effects of two cultivation modes (direct seeding and transplanting) and three irrigation methods (border irrigation, micro-spray tape irrigation, and surface drip irrigation) on cotton root traits and WUE. Results showed that transplanted cotton roots were predominantly concentrated in the 0–30 cm soil layer (75.35–77.13% of total root length), significantly higher than those of direct-seeded cotton (63.10–74.71%). Under micro-spray tape and drip irrigation, the root length density (RLD) of transplanted cotton was 18.55% and 23.46% higher, respectively, than that of direct-seeded cotton, whereas under border irrigation it was 5.09% lower. Transplanted cotton mainly extracted water from the 0–40 cm soil layer (utilization rate: 65.49%), while direct-seeded cotton primarily relied on water from the 20–60 cm layer (53.20%). Although no statistically significant difference in yield was observed between the two cultivation modes, transplanted cotton exhibited a 15.37% higher WUE than direct-seeded cotton. Moreover, surface drip irrigation substantially enhanced WUE, exceeding that under border irrigation and micro-spray tape irrigation by 37.35% and 14.07%, respectively. This study enhances understanding of root traits in transplanted cotton and demonstrates that irrigation methods regulate WUE by modifying root distribution and water uptake patterns.