Microbial life-history strategies mediate microbial carbon pump efficacy in response to N management depending on stoichiometry of microbial demand.

The soil microbial carbon pump (MCP) is increasingly acknowledged as being directly linked to soil organic carbon (SOC) accumulation and stability. Given the close coupling of carbon (C) and nitrogen (N) cycles and the constraints imposed by their stoichiometry on microbial growth, N addition might affect microbial growth strategies with potential consequences for necromass formation and carbon stability. However, this topic remains largely unexplored. Based on two multi-level N fertilizer experiments over 10 years in two soils with contrasting soil fertility located in the North (Cambisol, carbon-poor) and Southwest (Luvisol, carbon-rich), we hypothesized that different resource demands of microorganism elicit a trade-off in microbial growth potential (Y-strategy) and resource-acquisition (A-strategy) in response to N addition, and consequently on necromass formation and soil carbon stability. We combined measurements of necromass metrics (MCP efficacy) and soil carbon stability (chemical composition and mineral associated organic carbon) with potential changes in microbial life history strategies (assessed via soil metagenomes and enzymatic activity analyses). The contribution of microbial necromass to SOC decreased with N addition in the Cambisol, but increased in the Luvisol. Soil microbial life strategies displayed two distinct responses in two soils after N amendment: shift toward A-strategy (Cambisol) or Y-strategy (Luvisol). These divergent responses are owing to the stoichiometric imbalance between microbial demands and resource availability for C and N, which presented very distinct patterns in the two soils. The partial correlation analysis further confirmed that high N addition aggravated stoichiometric carbon demand, shifting the microbial community strategy toward resource-acquisition which reduced carbon stability in Cambisol. In contrast, the microbial Y-strategy had the positive direct effect on MCP efficacy in Luvisol, which greatly enhanced carbon stability. Such findings provide mechanistic insights into the stoichiometric regulation of MCP efficacy, and how this is mediated by site-specific trade-offs in microbial life strategies, which contribute to improving our comprehension of soil microbial C sequestration and potential optimization of agricultural N management.

Nitrogen leaching and grey water footprint affected by nitrogen fertilization rate in maize production: a case study of Southwest China.

BACKGROUND: Effective nitrogen (N) management measures are required to control environmental problems caused by N fertilizer use in intensive maize production systems. Soil N losses associated with high precipitation and over-fertilization in maize production can cause substantial environmental problems, whereas there is a lack of quantitative data and effective study countermeasures. A 2-year field study was conducted in the subtropical maize production system in Southwest China to quantify N leaching under varying N application rates of 0, 90, 180, 270 and 360 kg N ha-1  yr-1 . RESULTS: The results indicated that N leaching accounted for 16-38% of N fertilizer input. For farmer practice treatment (360 kg N ha-1  yr-1 ), N leaching loss was high at 110 kg N ha-1  yr-1 and accounted for 31% of the N applied. As an indicator of the ambient water quality pollution, the grey water footprint across all treatments ranged from 376 to 1092 m3 Mg-1 , with an average of 695 m3 Mg-1 . Reducing N rate to agronomically optimized treatment (180 kg N ha-1  yr-1 ) significantly decreased N leaching by 77%, and maintained high grain yield of 8.1 Mg ha-1 . The grey water footprint was reduced by 52-63% with N rates from 270 or 360 kg N ha-1  yr-1 to 180 kg N ha-1  yr-1 . CONCLUSION: Nitrogen surplus (applied N rate minus N uptake by maize) resulted in higher soil residual nitrate concentration and consequently high N leaching. High precipitation and low soil pH were the main ecological factors leading to high N leaching. © 2021 Society of Chemical Industry.

[Analysis on Driving Factors, Reduction Potential, and Environmental Effect of Inorganic Fertilizer Input in Chongqing].

In this study, we sought to quantify the effect of planting structure change on fertilizer input and environmental cost in Chongqing and develop scientific and rational strategies for chemical fertilizer reduction. Based on the crop fertilizer quota standard and large sample farmer survey data under the medium productivity level in Chongqing, we evaluated and analyzed the application reduction potential and environmental benefits of fertilizer with the difference method and life cycle assessment. The results showed that:① since Chongqing became a municipality directly under the central government (1997), Chongqing crop planting structure had greatly changed, and the proportion of food crop (rice, corn, wheat, bean, and potato) decreased by 21%. The area of fruits and vegetables increased from 3.36×105 hm2 to 1.05×106 hm2, and their proportion increased by 20%. ② Nearly 55% of fertilizers had been consumed by vegetable (37%) and citrus production systems, and 11%, 12%, and 12% of fertilizers were consumed by rice, corn, and potato, respectively. ③ The total fertilizer reduction of the Chongqing planting industry could reach up to 1.69×105 tons during the period of "the 14th Five-Year Plan," with a fertilizer reduction potential of 18.6%. The fertilizer reduction potential (reduction amount) of rice, corn, citrus, and vegetables would reach 0.3% (2.9×102 tons), 12% (1.45×104 tons), 21% (3.65×104 tons), and 30% (1.18×105 tons), respectively. On the other hand, the rape system was insufficient in phosphorus potassium fertilizers, and the corn tended to be insufficient in potash fertilizer. ④ The current production level was low, and the nitrogen loss, greenhouse gas emissions, and eutrophication potential in the planting industry of Chongqing reached 1.81×105 tons (N), 1.43×107 tons (CO2-eq), and 1.74×105 tons (PO4-eq). With the increase in the realization degree of the crop quota standard (60%-100%), the reactive nitrogen loss, greenhouse gas emissions, and eutrophication potential decreased by 14.9%-24.9%, 10.1%-16.7%, and 13.8%-23%, respectively. The structure of the planting industry in Chongqing significantly changed, the total fertilizer consumption in Chongqing tended to decline gradually, and the fertilization intensity of commercial crops stayed at a high level. The agricultural fertilizer reduction potential and the reactive nitrogen and greenhouse gas emission reduction potential were large, especially for citrus and vegetable production systems. However, it is also necessary to pay attention to insufficient corn potash fertilizer and rape phosphorus potassium fertilizer investment and carry out collaborative promotion of fertilizer reduction.

Optimizing Agronomic, Environmental, Health and Economic Performances in Summer Maize Production through Fertilizer Nitrogen Management Strategies.

Although nitrogen (N) fertilizer application plays an essential role in improving crop productivity, an inappropriate management can result in negative impacts on environment and human health. To break this dilemma, a 12-year field experiment (2008-2019) with five N application rates was conducted on the North China Plain (NCP) to evaluate the integrated impacts of optimizing N management (Opt. N, 160 kg N ha-1 on average) on agronomic, environmental, health, and economic performances of summer maize production. Over the 12-year study, the Opt. N treatment achieved the maximal average grain yield (10.6 Mg ha-1) and grain protein yield (793 kg ha-1) among five N treatments. The life cycle assessment methodology was applied to determine the negative impacts on environmental and human health, and both of them increased with the N rate. Compared with the farmers' conventional N rate (250 kg N ha-1), the Opt. N treatment reduced acidification, eutrophication, global warming, and energy depletion potentials by 29%, 42%, 35%, and 18%, respectively, and reduced the health impact by 32% per Mg of grain yield or grain protein yield produced. Both the Opt. N and Opt. N*50-70% treatments resulted in high private profitability (2038 USD ha-1), ecosystem economic benefit (1811 USD ha-1), and integrated compensation benefit (17,548 USD ha-1). This study demonstrates the potential benefits of long-term optimizing of N management to maintain high maize yields and grain quality, to reduce various environmental impacts and health impacts, and to enhance economic benefits. These benefits can be further enhanced when Opt. N was combined with advanced agronomic management practices. The results also suggest that reducing the optimal N rate from 160 to 145 kg N ha-1 is achievable to further reduce the negative impacts while maintaining high crop productivity. In conclusion, optimizing the N management is essential to promote sustainable summer maize production on the NCP.

Global food nutrients analysis reveals alarming gaps and daunting challenges.

Eliminating both overt and hidden hunger is at the core of the global food and nutrition security agenda. Yet, the collective state of nutrition security at the population level is not known. Here we quantify food-based availability of 11 essential nutrients for 156 countries using a food production-consumption-nutrition model, followed by assessment of the nutrient availability status as a ratio of recommended intake. For the baseline year 2017, global per capita availability was adequate for calorie and protein but in severe deficit for vitamin A and calcium (intake ratios, <0.60, where 1.0 is adequate) and moderate deficit for vitamin B12 (intake ratio, 0.76). At the country level, more than half of the 156 countries were in various degrees of deficit for all nine micronutrients. Disparities across regions or countries were enormous. We explore intervention strategies from an agriculture-food system perspective and discuss the daunting challenges of addressing nutrition security broadly.

Greenhouse gas emissions and mitigation potential of hybrid maize seed production in northwestern China.

Although hybrid maize seed production is one of the most important agriculture systems worldwide, its greenhouse gas (GHG) emissions and potential mitigation measures have not been studied. In this study, we used life cycle assessment (LCA) to quantify the GHG emissions of 150 farmers run by 6 companies in an area of northwest China known for hybrid maize seed production. The results indicated that the average reactive nitrogen (Nr) losses and GHG emissions from hybrid maize seed production were 53 kg N ha-1 and 8077 kg CO2 eq ha-1, respectively. Furthermore, the average nitrogen and carbon footprints of the process were 12.2 kg N Mg-1 and 1495 kg CO2 eq Mg-1, respectively. Nitrogen fertilizer and electricity consumption for irrigation were the main contributors to high GHG emissions, accounting for 60% and 30% of the total, respectively. The GHG emissions from seed production for different companies varied greatly with their resource input. There was also a large variation in environmental burdens among the 150 farmers. Based on an analysis of the yield group, we found that the carbon footprint of the first group (the one with the highest yield) was 27% lower than the overall average. Scenario analysis suggests that a combined reduction of N input rate, optimizing irrigation, and increasing yield can eventually mitigate the carbon footprint of hybrid maize seed production by 37%. An integrated systematic approach (e.g., ISSM: integrated soil-crop system management) can reduce the GHG emissions involved in producing hybrid maize seeds. This study provides quantitative evidence and a potential strategy for GHG emissions reduction of hybrid maize seed production.

Environmental impacts, human health, and energy consumption of nitrogen management for maize production in subtropical region.

Over-application of fertilizers could not improve crop yield and agronomic efficiency, but result in increasing nitrogen (N) surplus and adverse effects on the ecosystem sustainability. Although some previous studies have addressed one or a few environmental aspects in crop production, an integrated assessment for the effects of N fertilizer on multiple environmental impacts, and the optional steps of normalization and weighting is required. A consecutive 2-year plot-based field experiment was conducted with five N fertilizer levels (0, 90, 180, 270, and 360 kg N ha-1) in maize production at three sites in Southwest China, to evaluate the environmental performance and sustainability through joint use of life cycle assessment (LCA) and energy consumption analysis. Results demonstrated that the optimal N rate (180 kg N ha-1) showed greater potential for maintaining high yield (achieved 86% of the yield potential) and reducing the global warming (- 31%), acidification (- 47%), eutrophication (- 44%) compared to farmers' practice, and energy depletion potentials, by reducing pollutants emission during the production and transportation of N fertilizer and Nr losses at farm stage. Optimal N treatment indirectly reduced the land use, life-cycle human toxicity, aquatic eco-toxicity, and terrestrial eco-toxicity potentials by improving grain yield and agronomic efficiency. In addition, the optimal N treatment reduced the energy consumption by enhancing the energy use efficiency (EUE) (+ 74%) and reducing non-renewable energy form (- 45%) than the farmer's practice. This study will provide comprehensive information for both scientists and farmers involved in maize production and N management in subtropical region.

Carbon footprint of maize production in tropical/subtropical region: a case study of Southwest China.

Maize production is critical in tropical/subtropical regions, especially in developing countries where maize is a staple food. However, its environmental costs remain unclear. Southwest China is a tropical/subtropical region with large-scale maize production in each of its sub-regions. In the present study, we used Southwest China as a case study to evaluate the greenhouse gas (GHG) emissions and carbon footprint (CF) of maize production during 1996-2015 using life cycle assessment to identify the driving factors behind the GHG emissions and CF and to propose potential mitigation strategies. The mean GHG emissions of maize production per year during 1996-2015 was 4132 kg CO2-eq·ha-1, and the CF during this period was 961 kg CO2-eq·Mg-1. The GHG emissions and CF in Southwest China were 2-4 times higher than those of other major maize-producing regions worldwide. The GHG emissions and CF were both significantly correlated with the N surplus. The N surplus was also linearly correlated with annual precipitation, annual temperature and growing degree days, but not significantly related with soil pH. Scenario testing showed that the CF of maize production in Southwest China could be reduced by 41%, i.e. to 437 kg CO2-eq·Mg-1, by farmers adopting a comprehensive strategy including recommended fertiliser application rates, innovative fertilisers, and crop management to decrease GHG emissions and achieve the yield potential in the region. Integrated soil and crop management is essential for sustainable maize production in tropical/subtropical regions with complex and changeable ecological conditions, especially in developing countries where maize is a staple food.

Global direct nitrous oxide emissions from the bioenergy crop sugarcane (Saccharum spp. inter-specific hybrids).

Sugarcane is the second largest bioenergy crop in the world and it accounts for 80% of global sugar production. Grown mostly in wet and warm tropics with relatively high nitrogen (N) fertiliser input and crop residue retention, sugarcane production is a significant source of nitrous oxide (N2O) emission. Yet, a global evaluation of research on N2O emission from sugarcane crop is lacking. Here, we conducted a meta-analysis using data from 141 measurements compiled from 15 sugarcane field studies reported from different countries to i) quantify N2O emissions and emission factors (EFs) globally, and for tropics and sub-tropics, and ii) identify the key factors that promote N2O emission. Our analysis shows that the global mean total N2O emission from sugarcane production reached 2.26 (CI: 1.93-2.62) kg N2O-N ha-1 yr-1 with an estimated EF of 1.21% (CI: 0.971-1.46%). N2O emissions increased exponentially with increase in N fertiliser rate, questioning the adequacy of Intergovernmental Panel on Climate Change (IPCC) default EF value (1%) for sugarcane N2O emission estimation. Mean total N2O emissions and EFs in tropics and sub-tropics did not vary significantly. Supplementing synthetic N fertiliser (SN) with organic amendments (OA) significantly increased mean N2O emission (~1.4-fold) and EF (~2.5-fold) compared to SN. A remarkable reduction in N2O emission (38.6%) and EF (61.5%) was evident when enhanced efficiency fertilisers (EEF) replaced SN. In contrast, crop residue removal had little impact on N2O emission and EF, but both parameters showed an upward trend with irrigation and increased rainfall. Soil carbon content and pH were emerged as key regulators of sugarcane N2O emission and EF. It is concluded that global sugarcane N2O emission could be significant and that there is considerable prospect for mitigating the emission through innovative nutrient formulations and precision agriculture that help meet crop nutrient demand without compromising environmental imperatives.

Identifying key drivers for geospatial variation of grain micronutrient concentrations in major maize production regions of China.

Micronutrient deficiencies are prevalent health problems worldwide. The maintenance of adequate concentrations of micronutrients in maize grain is crucial for human health. We investigated the overall status and geospatial variation of micronutrients in Chinese maize grains and identified their key drivers. A field survey was conducted in four major maize production areas of China in 2017 with 980 pairs of soil and grain samples collected from famers' fields. At a national scale, grain zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) concentrations varied substantially, with average values of 17.4, 17.3, 4.9, and 1.5 mg kg-1, respectively, suggesting a solid gap between grain Zn and Fe concentrations and the biofortification target values. Significant regional difference in the concentrations of Zn, Mn and Cu, but not Fe, were observed in grain, with much higher levels in Southwest China. The nutritional yields of Zn, Fe and Cu were lower than the energy and Mn yields, indicating an unbalanced output between energy and micronutrients in current maize production system. Grain Zn, Fe, Mn and Cu correlated negatively with maize yield in most test regions. Increased nitrogen (N) rate positively affected grain Zn and Cu, while increased phosphorus (P) rate negatively affects grain Zn and Fe. Apart from Fe, available Zn, Mn and Cu in soil exerted significant positive effects on grain Zn, Mn and Cu concentrations, respectively. Decrease in soil pH and increase in the organic matter content may increase the accumulation of Fe and Mn in grain. Grain Zn and Cu concentrations increased as available soil P decreased. Of the factors considered in this study, grain yield, N and P rates, soil pH and organic matter were the main factors that affect grain micronutrient status and should be more extensively considered in the production and nutritional quality of maize grain.

The effects of controlled release urea on maize productivity and reactive nitrogen losses: A meta-analysis.

Application of controlled release urea (CRU) is recommended to reduce the undesirable environmental effects resulting from urea application. However, the overall effects of CRU on maize productivity and reactive nitrogen (N) losses remain unclear. Our global meta-analysis based on 866 observations of 120 studies indicated that application of CRU instead of urea (same N rate) increased maize yield by 5.3% and nitrogen use efficiency (NUE) by 24.1%, and significantly decreased nitrous oxide (N2O) emission, N leaching and ammonia (NH3) volatilization by 23.8%, 27.1% and 39.4%, respectively. The increase of NUE and reduction of N2O emission by CRU application were greater with medium and high N rates (150 ≤ N < 200 and N ≥ 200 kg N ha-1) than with low N rates. The reduction in N2O emission and N leaching with CRU application were enhanced when soil organic carbon (SOC) content was <15.0 g kg-1, and soil texture was medium or coarse. The reduction in N2O emission and NH3 volatilization with CRU were greater in soils with pH ≥ 6.0. We concluded that use of CRU should be encouraged for maize production, especially on light-textured soils with low organic matter content.

Nitrous oxide emissions in Chinese vegetable systems: A meta-analysis.

China accounts for more than half of the world's vegetable production, and identifying the contribution of vegetable production to nitrous oxide (N2O) emissions in China is therefore important. We performed a meta-analysis that included 153 field measurements of N2O emissions from 21 field studies in China. Our goal was to quantify N2O emissions and fertilizer nitrogen (N) based-emission factors (EFs) in Chinese vegetable systems and to clarify the effects of rates and types of N fertilizer in both open-field and greenhouse systems. The results indicated that the intensive vegetable systems in China had an average N2O emission of 3.91 kg N2O-N ha-1 and an EF of 0.69%. Although the EF was lower than the IPCC default value of 1.0%, the average N2O emission was generally greater than in other cropping systems due to greater input of N fertilizers. The EFs were similar in greenhouse vs. open-field systems but N2O emissions were about 1.4 times greater in greenhouses. The EFs were not affected by N rate, but N2O emissions for both open-field and greenhouse systems increased with N rate. The total and fertilizer-induced N2O emissions, as well as EFs, were unaffected by the type of fertilizers in greenhouse system under same N rates. In addition to providing basic information about N2O emissions from Chinese vegetable systems, the results suggest that N2O emissions could be reduced without reducing yields by treating vegetable systems in China with a combination of synthetic N fertilizer and manure at optimized economic rates.