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Under today’s climate warming, mitigating the risks of soil organic carbon (SOC) decomposition in cropping systems is critical to maintain carbon sequestration. This study posits that nitrogen addition rate and duration are the key factors influencing the responses of soil heterotrophic respiration (Rh) to climate warming in a cropping system. Based on soil sampled from traditional-agriculture rice-growing regions in the Taihu Lake Basin in eastern China, this study aimed to clarify how nitrogen addition strategies affect soil Rh and its temperature sensitivity (Q10) and to explore the underlying mechanisms of the changes in soil environment that influence carbon emissions under nitrogen addition through the Rh pathway. The results demonstrate that, with the increasing duration of nitrogen addition, soil Rh and its Q10 were initially increased but subsequently suppressed, and the inhibitory effect on soil Rh became apparent after six years of continuous addition. Further analysis revealed that decreases in C/N, pH, and extractable organic nitrogen and increases in mineral nitrogen are the primary factors suppressing soil Rh. These findings indicate that an optimized nitrogen addition strategy tailored to specific crops could achieve profitable crop yields while effectively mitigating the promoting effect of climate warming on SOC decomposition.

Cropland is a main source of global nitrogen pollution 1 , 2 . Mitigating nitrogen pollution from global croplands is a grand challenge because of the nature of non-point-source pollution from millions of farms and the constraints to implementing pollution-reduction measures, such as lack of financial resources and limited nitrogen-management knowledge of farmers 3 . Here we synthesize 1,521 field observations worldwide and identify 11 key measures that can reduce nitrogen losses from croplands to air and water by 30–70%, while increasing crop yield and nitrogen use efficiency (NUE) by 10–30% and 10–80%, respectively. Overall, adoption of this package of measures on global croplands would allow the production of 17 ± 3 Tg (10 12  g) more crop nitrogen (20% increase) with 22 ± 4 Tg less nitrogen fertilizer used (21% reduction) and 26 ± 5 Tg less nitrogen pollution (32% reduction) to the environment for the considered base year of 2015. These changes could gain a global societal benefit of 476 ± 123 billion US dollars (USD) for food supply, human health, ecosystems and climate, with net mitigation costs of only 19 ± 5 billion USD, of which 15 ± 4 billion USD fertilizer saving offsets 44% of the gross mitigation cost. To mitigate nitrogen pollution from croplands in the future, innovative policies such as a nitrogen credit system (NCS) could be implemented to select, incentivize and, where necessary, subsidize the adoption of these measures. A meta-analysis of 1,521 field observations from the past two decades led to the identification of 11 key measures to cost-effectively mitigate nitrogen pollution from global croplands.

China’s agriculture is dominated by smallholder farms, which have become major sources of negative environmental impacts including eutrophication, formation of haze, soil acidification and greenhouse gas emissions. To mitigate these environmental impacts, new farming models including family farming, cooperation farming and industrial farming have emerged in recent years. However, whether these new farming practices would improve the economic and environmental performance as compared to the current smallholder farming has yet to be verified on ground level. In this paper, by using pilot farming cases within the watershed of Tai Lake, we found that alternative farming models produced 7% more crop yield, while using 8% less fertilizer, leading to a 28% decrease in pollutant emission per hectare. These alternative farming models have a 17% higher fertilizer use efficiency and 50% higher profit per hectare. Compared to smallholder farming, these alternative farming practices invest 27% more resources into agricultural facilities, including advanced machinery, and have a younger, better educated labor force as a consequence of a larger farm size and more specialization. These input changes substantially increase fertilizer use efficiency and reduce agricultural pollution. Policy arrangements to support and facilitate the uptake of these farming models will further promote the green development and sustainable intensification of agricultural production. Graphical abstract

In the Tailake region of China, heavy nitrogen (N) loss of rice-wheat rotation systems, due to high fertilizer-N input with low N use efficiency (NUE), was widely reported. To alleviate the detrimental impacts caused by N loss, it is necessary to improve the fertilizer management practices. Therefore, a 3 yr field experiments with different N managements including organic combined chemical N treatment (OCN, 390 kg N ha−1 yr−1, 20% organic fertilizer), control-released urea treatment (CRU, 390 kg N ha−1 yr−1, 70% resin-coated urea), reduced chemical N treatment (RCN, 390 kg N ha−1 yr−1, all common chemical fertilizer), and site-specific N management (SSNM, 333 kg N ha−1 yr−1, all common chemical fertilizer) were conducted in the Taihu Lake region with the 'farmer's N' treatment (FN, 510 kg N ha−1 yr−1, all common chemical fertilizer) as a control. Grain yield, plant N uptake (PNU), NUE, and N losses via runoff, leaching, and ammonia volatilization were assessed. In the rice season, the FN treatment had the highest N loss and lowest NUE, which can be attributed to an excessive rate of N application. Treatments of OCN and RCN with a 22% reduced N rate from FN had no significant effect on PNU nor the yield of rice in the 3 yr; however, the NUE was improved and N loss was reduced 20-32%. OCN treatment achieved the highest yield, while SSNM has the lowest N loss and highest NUE due to the lowest N rate. In wheat season, N loss decreased about 28-48% with the continuous reduction of N input, but the yield also declined, with the exception of OCN treatment. N loss through runoff, leaching and ammonia volatilization was positively correlated with the N input rate. When compared with the pure chemical fertilizer treatment of RCN under the same N input, OCN treatment has better NUE, better yield, and lower N loss. 70% of the urea replaced with resin-coated urea had no significant effect on yield and NUE improvement, but decreased the ammonia volatilization loss. Soil total N and organic matter content showed a decrease after three continuous cropping years with inorganic fertilizer application alone, but there was an increase with the OCN treatment. N balance analysis showed a N surplus for FN treatment and a balanced N budget for OCN treatment. To reduce the environmental impact and maintain a high crop production, proper N reduction together with organic amendments could be sustainable in the rice-wheat rotation system in the Taihu Lake region for a long run.

Intensive irrigated rice-wheat crop systems have caused serious soil depletion and nitrogen loss in the Tai Lake region of China. A possible solution is the incorporation of legumes in rice because legumes are a source of nitrogen. There is actually little knowledge on the impact of legumes on rotation, soil fertility, and nitrogen loss. Therefore, we studied the effect of five rice-based rotations, including rice-wheat, rice-rape, rice-fallow, rice-bean, and rice-vetch, on soil nitrogen, rice yield, and runoff loss. A field experiment was conducted in the Tai Lake region from 2009 to 2012. Crop residues from rape, bean, and vetch were used to partially replace chemical fertilizer in rice. Results show that replacing 9.5–21.4 % of mineral nitrogen fertilizer by residues maintained rice yields of rice-rape, rice-bean, and rice-vetch rotations, compared to the rice-wheat reference. Moreover, using legumes as a winter crop in rice-bean and rice-vetch combinations increased rice grain yield over 5 %, and increased rice residue nitrogen content by 9.7–20.5 %. Nitrogen runoff decreased 30–60 % in rice-rape, rice-bean, and rice-vetch compared with rice-wheat. Soil mineral nitrogen and microbial biomass nitrogen content were also improved by application of leguminous residues.

(1) Background: Excessive nitrogen (N) fertilizer application in tea plantations leads to challenges such as soil acidification and nitrogen loss, impending the sustainable development of the plantation system. Yet, there is a lack of research on blended fertilization strategies, and limited data regarding N loss when substituting with organic fertilizer. (2) Methods: A year-long field monitoring experiment was conducted to evaluate the effects of substituting compound fertilizer with organic fertilizer, specifically with respect to runoff N loss and uptake of chemical fertilizer N by tea trees. (3) Results: The annual runoff N loss ranged from 0.16 to 0.57 kg·hm−2 and accounted for a mere 0.22–0.48% of N from fertilizer applications. Substitution with organic fertilizer reduced runoff N loss by 21–53% and improved the tea tree utilization efficiency of chemical fertilizer N from 16% to 27%. A 50% organic fertilizer substitution (based on the amount of N) promoted a net soil N mineralization rate, creating an ammonium-rich environment favored by tea trees. (4) Conclusions: The positive effects of partially substituting N fertilizer with organic fertilizer in tea plantation systems on both N utilization efficiency and N loss were confirmed. If conditions permit, the study team would aim to expand the temporal scope of the study, and to investigate the impact of organic fertilizer substitution on N loss under various precipitation intensities.

Recovering nitrogen (N) from agricultural wastewater for reuse in planting fields is a more sustainable and economical strategy to limit N pollution than using conventional treatments. Hereby, regular biochar produced by wheat straw pyrolysis and Mg-modified biochar were used as the N carriers to assess inorganic-N adsorption from simulated agricultural wastewater and the potential for reuse of the carried N in a planting system. The results showed that biochar materials have different affinities towards inorganic-N types. The amount of biochar carried-N increased with the increase in inorganic-N concentration and reached 4.44 mg/g as the maximum. The biochar carried ~4 mg/g of inorganic N substituting nearly 40% of N fertilizer following a 1% w/w addition rate for vegetable planting. After a trial season, 34.7–42.7% of the carried N from biochar was assimilated by the plant, 45.9–53.7% was retained by the soil, and only about 10% was lost. In comparison to the condition with all N inputs from chemical fertilizer, the addition of part of N by the N–biochar matrix significantly reduced the N loss by improving the plant N uptake or increasing the N content in the soil. This study demonstrates that biochar materials could be used as N carriers to recover N from wastewater for reuse in soil, carrier stability, and bioavailability preservation.

Full time-space governance strategy for AGNPS pollution was proposed. The 4R chain technology system including source reduction, process retention, nutrient reuse and water restoration was reviewed. The strategy and 4R technology system was successfully applied for AGNPS pollution control at administrative village scale. Future challenge include the monitoring system, new smart fertilizer and intelligent equipment, governance standards and supportive policies. Ensuring food safety while reducing agricultural non-point source pollution is quite challenging, especially in developing and underdeveloped countries. Effective systematic strategies and comprehensive technologies need to be developed for agricultural non-point source pollution control at the watershed scale to improve surface water quality. In this review, a proposal is made for a full time-space governance strategy that prioritizes source management followed by endpoint water pollution control. The 4R chain technology system is specifically reviewed, including source reduction, process retention, nutrient reuse and water restoration. The 4R chain technology system with the full time-space governance strategy was applied at the scale of an administrative village and proved to be a feasible solution for reducing agricultural non-point source pollution in China. In the future, a monitoring system needs to be established to trace N and P transport. Additionally, new smart fertilizer and intelligent equipment need to be developed, and relevant governance standards and supportive policies need to be set to enhance the efficacy of agricultural non-point source pollution control.

To effectively remove phosphate pollution and convectively reuse phosphate resource, straw biochar was firstly functionalized with lanthanum ferrite (LaFeO 3 ) via four different methods, including one-step co-precipitation ( S-C ), two-step co-precipitation ( B-C ), one-step impregnation ( S-E ), and two-step impregnation ( B-E ). LaFeO 3 /biochar was characterized systematically by a series of characterization methods. The influence of preparation methods, operation conditions on adsorption process, and the regenerability were studied. The products prepared by four methods displayed different physical morphology and chemical analysis proved chemical composition were similar. LaFeO 3 /biochar exhibited high adsorption capacity, the pseudo-second-order and Sips models were fitted for the adsorption equilibrium. The LaFeO 3 /biochar exhibited outstanding phosphate adsorption performance with pH values ranging from 2.3 to 10.6; La ions release was similarly negligible, when pH value was higher than 5.27. The adsorption mechanism was studied and inferred that La species is the key to adsorption ability. The results obtained provide better understanding of the adsorption phenomena and indicate the available preparation technologies and potential usefulness of LaFeO 3 /biochar for removing phosphate pollution. Graphical abstract “.”

A floating bed system vegetated with Oenanthe javanica was adopted in this study to treat two types of low-pollution wastewater (LPW): polluted river water (PRW) and treated domestic wastewater (DW). The water was treated for 111 days during the low-temperature season. The results indicated that the total nitrogen (TN) removal rates were higher in the DW groups than in the PRW groups during the initial 30 days. This difference may stem from the different C/N ratio of the influent. As the water temperature rose above 15.5 °C after March 12, the purification capability of nitrogen in the DW groups was enhanced, and the removal rates of TN were 89.8 and 76.8 % in DW and the control 2 at 111 days. Conversely, the performance of total phosphorus (TP) removal was robust during the initial stage of the experiment, despite receiving domestic wastewater with a relatively high N/P ratio (16:1). The TP removal rates in DW were as high as 91.5 % compared to 78.9 % in PRW at 30 days. At the same time, the N/P ratios of plant tissue were higher in the DW groups compared to that in the PRW groups. Plant uptake played a significant role in nutrient removal in the PRW groups (52.5 % for TN, 68.2 % for TP), followed by sedimentation. In contrast, plant uptake only accounted for 25.3 % of TN removal and 24.1 % of TP removal in DW. The results provide engineering parameters for the future design of an ecological remediation technology for LPW purification.