Using Critical Zone Science to Enhance Soil Fertility and Improve Ecosystem Services for Peri-Urban Agriculture in China

本研究以中国城郊高产农区农业可持续集约化为研究对象。这个农业基地对满足中国日益增长的粮食生产需求至关重要，但也面临着城市污染投入、耕作方式造成的土壤和水污染--尤其是矿物质化肥和杀虫剂的广泛使用以及城市化--的压力。我们将量化大幅度增加有机肥料应用的好处和风险，以此作为减少无机肥料使用的一种手段。我们的方法是研究土壤作为地球临界区(CZ)的中央控制点的作用，CZ是我们星球的薄外层，决定了大多数维持生命的资源。我们的临界区观测站(CZO)位于长三角快速城市化试点城市宁波市内的樟溪流域。我们将结合增加有机肥料负荷的受控操纵实验，确定土壤过程速率，并确定跨通量边界的水、养分、污染物和温室气体(GHG)排放的通量，其中土壤剖面与更广泛的CZ、地表水和含水层、植被和大气交界并对其产生影响。为了指导研究设计，我们确定了3个详细的科学假设。有机肥取代无机肥的使用将使土壤N/C循环的食物网从以细菌异养分解土壤有机质(SOM)和细菌硝化作用产生植物有效氮和向排水流失可溶性硝酸盐为主，转变为以异养真菌分解复杂的、更持久的OM为主导的植物可利用的低分子有机N形式。氮源的这种变化将通过土壤团聚体的形成增加土壤有机质含量，改善土壤结构。更多地使用猪粪(PS)和废水污泥(WS)中的有机肥料将导致环境中新出现的污染物增加，特别是抗生素和生长激素。必须确定环境运输、命运和暴露，以量化微生物抗生素耐药性的发展和其他环境和食品安全风险，并制定减少风险的土壤和水管理做法。减少使用矿物肥料和增加使用有机肥料将减少金属污染带来的环境和食品安全风险；这是由于氧化还原转化降低了金属的流动性和生物有效性，减少了土壤酸化和增加了土壤有机质的金属络合作用。我们的研究计划将通过嵌套的观察尺度进行操纵实验，包括理想化的实验室微观世界系统、田间中观系统的受控操纵实验、减少新污染物从土壤到地表水的传输的草地缓冲带的初步测试，以及野外(~1公顷)操纵实验。机制土壤过程模型将被测试，并进一步发展以测试特定的假设，并应用于量化调节景观尺度CZ通量的过程速率，作为生态系统服务流的衡量标准。地理信息系统建模方法包括从流域更广泛位置的土壤属性和过程速率的子集的特征描述数据，以及对水和溶质通量平衡的流域地表水和地下水监测。开发的地理信息系统模型将确定营养物、污染物和温室气源和汇的地理空间变化，并将用于量化集水区尺度的通量。这些结果将确定当前生态系统服务流量的基线，并将评估生态系统服务的这些衡量标准将如何随着过渡到在流域农业区广泛使用有机化肥而发生变化的情景。

This research project focuses on sustainable intensification of agriculture in highly productive peri-urban farming areas in China. This agricultural base is essential to meet China's increasing food production demands but is under pressure from urban pollution inputs, soil and water pollution from farming practices - particularly extensive use of mineral fertilisers and pesticides, and urbanisation. We will quantify the benefits and risks of a substantial step-increase in organic fertiliser application as a means to reduce the use of mineral fertiliser. Our approach is to study the role of soil as a central control point in Earth's Critical Zone (CZ), the thin outer layer of our planet that determines most life-sustaining resources. Our Critical Zone Observatory (CZO) site is the Zhangxi catchment within Ningbo city, a pilot city of rapid urbanization in the Yangtze delta. We will combine controlled manipulation experiments of increased organic fertiliser loading with determination of soil process rates and flux determinations for water, nutrients, contaminants, and greenhouse gas (GHG) emissions across the flux boundaries where the soil profile interfaces with and influences the wider CZ; surface waters and aquifers, vegetation, and the atmosphere. To guide the research design we have identified 3 detailed scientific hypotheses.1. Replacement of mineral fertiliser use by organic fertiliser will shift the soil food web for N/C cycling from one dominated by bacterial heterotrophic decomposition of soil organic matter (SOM) and bacterial nitrification to produce plant available N and loss of soluble nitrate to drainage waters, to one dominated by heterotrophic fungal decomposition of complex, more persistent forms of OM to low molecular weight organic N forms that are plant available. This change in N source will increase SOM content and improve soil structure through soil aggregate formation.2. Increased use of organic fertiliser from pig slurry (PS), and wastewater sludge (WS) will lead to increased environmental occurrence of emerging contaminants, particularly antibiotics and growth hormones. Environmental transport, fate and exposure must be determined to quantify development of microbial antibiotic resistance and other environmental and food safety risk, and develop soil and water management practices for risk mitigation.3. Decreased use of mineral fertilisers and increased use of organic fertilisers will reduce environmental and food safety risks from metals contamination; this is due to lower metal mobility and bioavailability from redox transformations, reduced soil acidification and increased metal complexation on soil organic matter.Our programme of research will conduct the manipulation experiments across nested scales of observation with idealised laboratory microcosm systems, controlled manipulation experiments in field mesocosms, pilot testing of grass buffer strips to reduce the transport of emerging contaminants from the soil to surface waters, and field (~1ha) manipulation experiments. Mechanistic soil process models will be tested, further developed to test the specific hypotheses, and applied to quantify process rates that mediate the landscape scale CZ fluxes as a measure of ecosystem service flows. GIS modelling methods include data from characterisation of a subset of soil properties and process rates at a wider set of locations in the catchment, together with catchment surface water and groundwater monitoring for water and solute flux balances. The GIS model that is developed will identify the geospatial variation in nutrient, contaminant, and GHG sources and sinks and will be used to quantify fluxes at the catchment scale. These results will determine the current baseline of ecosystem service flows and will evaluate scenarios for how these measures of ecosystem services will change with a transition to widespread of organic fertilisers through the farming area of the catchment.