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

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.

This project develops a closely integrated project between research teams in the UK and China that directly addresses the following sustainable development challenges of China.

1. Economic development through innovation in agricultural practices
2. Food security through improved agricultural yields on existing productive land
3. Food safety through decreases in plant available soil contaminants
4. Water quality protection and improvement through reduced soil pollution
5. Wellbeing of urban inhabitants through peri-urban land management
6. Ecological resilience of agricultural production to environmental change
7. Meeting environmental commitments through reduced greenhouse gas emissions from land
8. Agricultural nutrient resource recovery from animal and human food consumption
9. The environmental impacts of urbanisation

The project addresses the challenges effectively by linking the research activities with innovation in farming practices through field manipulation experiments that act as testbeds and demonstrations for the use of organic fertilisers. The project addresses the challenges efficiently by focusing on the role of soil as a central control point within the integrated Critical Zone (CZ) system where positive changes in managing soil fertility can influence multiple beneficial outcomes to the development challenges. Efficiency of research investment is gained by drawing on the current investment in staff and infrastructure by the principal China partner (IUE) at the site and through collaboration with the Zhejiang Academy of Sciences Agricultural Institute in Ningbo city. The programme of impact activities includes strong UK and China stakeholders and performance metrics for immediate and long-term impact are defined. UK strengths in novel, high throughput molecular tools for soil food web dynamics will be applied with the Chinese investigators at the Ningbo CZO. This will provide the scientific evidence on how in organic fertiliser application will impact the soil N-cycle and can be pro-actively managed to improve yields and long-term soil fertility for food security. UK strengths in novel isotope biogeochemistry will be carried out jointly with the Chinese partners and will provide the scientific evidence to optimise soil management practices that reduce toxic metals uptake to food crops, to improve food safety. UK strengths for in situ quantitative analysis of emerging contaminants will develop novel biosensor technology and deploy it in the manipulation experiments in China. This will provide the scientific evidence for soil management practices to reduce the flux of contaminants to surface and groundwater. This will protect and improve water quality and help reduce the occurrence of environmental antibiotic resistance. UK strengths in mechanistic soil process modelling that is integrated with CZ flux determinations will be applied to interpret the results of the field manipulation experiments. The modelling will provide the scientific evidence to guide practice in organic fertiliser use to potentially benefit: crop yields, soil and water quality, ecological resilience to atmospheric deposition of urban contaminants, and reduced greenhouse gas emissions from land. Additional impacts include the potential for improved yields to help livelihoods and reduce poverty in farming communities. Joint design and delivery of manipulation experiments with farmers will support early identification and adoption of improved soil management practices. Organic fertilisers increase soil organic matter content which improves soil pore structure through aggregate formation. This increases plant-available water-holding capacity for drought resilience, and increases interaggregate water drainage for flood resilience. Reduced mineral fertiliser use will cut the life-cycle costs of the carbon footprint of manufacturing, greenhouse gas emissions from land, and increased water pollution from nutrient leaching.