Long-term large inputs of phosphorus (P) fertilizer in China have caused serious soil P accumulation, low P use efficiency (PUE) and high risk of P loss. Controlling the amount of P fertilizer applied presents an inevitable choice for improving the PUE. Struvite recycled from agricultural wastewater rich in N and P concentrations are capable of slow nutrient release, improving nutrient uptake and enabling the reuse of nutrients from environmental sources when applied to agricultural land. A two-year field experiment was conducted to investigate the effects of struvite combined with P reduction under a rice–wheat rotation system in eastern China. A total of five treatments were set up, including conventional fertilization (FP), a struvite substitution of 100% P fertilizer (SP), a 50% P reduction with struvite substitution (RSP), no application of N fertilizer (N0) and no application of P fertilizer (P0). Grain yield, crop N and P uptake, N and P use efficiency (NUE and PUE) and soil nutrient status were assessed. Under the same P application rate, the yield and aboveground biomass of the SP treatment were slightly higher than those of FP treatment, but the crop P uptake, PUE and soil available P content were significantly increased. The RSP treatment did not reduce yield with 50% P reduction, and significantly improved the PUE and soil available P content. Crop N uptake and NUE were also found to be increased in SP and RSP treatments with struvite substitution. The P apparent balance showed that both the SP and FP treatments had a P surplus, but the RSP treatment had a P break-even, and the soil available P content remains stable compared with the initial value. The results indicate that struvite application could improve the soil P availability and crop nutrient uptake then promote the crop yield. To increase the nutrient use efficiency of crops while ensuring crop yield and soil fertility, appropriate P reduction combined with struvite as a P fertilizer could be sustainable in the rice–wheat rotation system in the long run.

Clarifying the benefits of carbon sequestration and crop production of continuous green manure amendment is crucial for sustainable agricultural development. Here, using a long-term located experiment, we assessed the effects of 18 years’ ryegrass/milk vetch amendment with (NF, 150 kg N ha⁻¹) or without nitrogen (N) fertilizer input (CK), on soil carbon management indices, paddy methane (CH₄) emissions and rice yields. The results showed that green manure, rather than fertilization, played a critical role in soil CMI, increasing the carbon pool index but reducing the carbon management index. The increased soil organic carbon and the reduced labile organic carbon were the main causes for this performance. Additionally, the effects of both fertilization and green manure amendment on CH₄ emissions were insignificant; however, fertilization significantly increased grain yield by 39.30% compared to CK. As a result, the methane emission intensity under fertilization treatment was notably lower than that from CK. The findings suggest that green manure amendment is a profitable manipulation for enhancing carbon sequestration without increasing paddy CH₄ emissions. However, this cannot substitute the critical role of N fertilizer in rice production.

Introduction: This study aimed to assess the influence of experimental warming and fertilization on rice yield and paddy methane emissions. Methods: A free-air temperature increase system was used for the experimental warming treatment (ET), while the control treatment used ambient temperature (AC). Each treatment contained two fertilization strategies, (i) normal fertilization with N, P and K fertilizers (CN) and (ii) without N fertilizer input (CK). Results: The yield was remarkably dictated by fertilization (p < 0.01), but not warming. Its value with CN treatment increased by 76.24% compared to CK. Also, the interactive effect of warming and fertilization on CH₄ emissions was insignificant. The seasonal emissions from warming increased by 36.93% compared to AC, while the values under CN treatment increased by 79.92% compared to CK. Accordingly, the ET-CN treatment obtained the highest CH₄ emissions (178.08 kg ha⁻¹), notably higher than the other treatments. Also, the results showed that soil fertility is the main driver affecting CH₄ emissions rather than soil microorganisms. Conclusions: Fertilization aggravates the increasing effect of warming on paddy methane emissions. It is a daunting task to optimize fertilization to ensure yield and reduce methane emissions amid global warming.

What strategy of nutrient management can maintain the high and stable annual yield in rice–wheat systems under climate change? A 10-year term experiment was conducted in the rice–wheat system to investigate the effect of optimal nutrient management on crop yield and meteorological drivers of year-to-year fluctuations in rice and wheat yield. Treatments were as follows: conventional fertilization (CF, as control), fertilizer postponing (FP, with the same amount fertilization as CF and increasing rate and times of panicle fertilizer) with/without straw incorporation (including only straw returned in rice (W) or wheat (R) season, and both straw incorporation (WS), RFP (reducing amount based on FP) with/without organic fertilizer. Results showed that FP with/without straw incorporation increased 10-year average yields of rice, wheat, and annual by 4.5~6.5%, 3.8~7.2%, and 4.8~6.8%, respectively, while RFP with/without organic fertilizer did not markedly reduce wheat yield, compared with CF. Effect of optimal treatments on wheat and rice yield stability was different; among the annual yield stability in FP + WRS was the greatest due to increasing and a stable number of spikelets and dry matter accumulation (DMA) after heading. Furthermore, the coefficient of variation (CV) of DMA during rice jointing-heading (21.6~30.0%) and heading-maturity stage (20.1~27.9%) was higher than before jointing (13.9~16.7%), which were affected by day photosynthetically active radiation (explain: 26%) and the number of rainy days (explain: 34%), respectively, using Stepwise regression; in contrast, in wheat season, the fluctuation of DMA before jointing was the highest (CV: 83.8~109.9% (before jointing) vs. 61.1~97.4% (heading-mature stage) vs. 33.7~46.3% (jointing-heading period), 55% of its variations was impacted by day-night temperature differences, the number of rainy days and photosynthetically active radiation accumulation. Our finding suggested that nutrient management to increase and stable the DMA after rice jointing and before wheat jointing could maintain the high and stable annual yield in rice–wheat systems.

Constructed wetlands (CWs) are effective wastewater treatment systems, relying on plant and substrate uptake and microbial depletion to remove pollutants. It has been reported that melatonin can promote plant growth and change the structure of microbial communities. The effects of melatonin on stress tolerance of plants have been extensively studied, while the effects of melatonin on the efficiency of wastewater treatment in constructed wetlands are rarely known. In the current study, 1 mM melatonin was added to the constructed wetland systems to determine physiological characteristics of Phragmites australis, microbial enzyme activity, and microbial community structure of CWs. Under melatonin treatment, the An and g_s of Phragmites australis plants were significantly improved compared with the control. In addition, the contents of phosphate and total anion in the xylem sap of Phragmites australis significantly increased. However, the concentration of total phosphorus in the effluent did change significantly. Melatonin treatment improved the dehydrogenase activity and significantly improved the removal efficiency of NH₄⁺-N in CWs. Furthermore, melatonin reduced the richness of the microbial community in CWs, while it increased the diversity of bacterial community and altered microbial composition. FARPROTAX analysis showed that melatonin increased the abundance of bacteria involved in nitrogen fixation and ureolysis, which may be related to the improvement of plant photosynthetic performance and improved rhizosphere oxygen environment. These results suggested that melatonin may affect plant performance and microbial composition and functions to improve the purification effect of constructed wetland.