[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.

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.