Agroforestry, soil health and delivery of public goods

This project provides an exciting and timely opportunity to contribute to our knowledge of  the impacts of agroforestry on soil health and delivery of wider ecosystem services in temperate ecosystems 

Agroforestry is the practice of deliberately growing trees in combination with arable crops and/or pasture on the same piece of land (Figure 1). Agroforestry is seen as a sustainable land management practice, where trees and agriculture co-exist to provide multiple benefits. Therefore growth and innovation in agroforestry has the potential to improve farmland productivity, resilience and diversity while maintaining and/or improving the provision of other ecosystem services, via improving soil health (Dollinger & Jose, 2018;), sequestering carbon (De Stefano & Jacobson, 2018; Lorenz & Lal, 2014) and slowing water runoff (Marshall et al., 2009). While long-established in sub-tropical and tropical climates, uptake of agroforestry in temperate agricultural systems has been slow, particularly in the UK (Woodlands Trust, 2018). In order to realize this potential, there is urgent need for greater understanding of how planting trees in temperate agricultural systems impacts upon soil health indicators and thus helps to reduce flooding and mitigate climate change.

Figure 1 (a) Silvopastoral system in which trees are mixed with grazing animals and (b) Silvoarable system in which trees are planted in rows with an arable crop in the alleys between.

While literature reviews have shown that agroforestry can increase the amount of carbon stored in the soil (De Stefano & Jacobson, 2018; Lorenz & Lal, 2014) and thus help to mitigate climate change, the majority of studies (~80%) were located in tropical and sub-tropical climates, with less than 20% in temperate climates. Oelbermann et al. (2014) found that in temperate zones agroforestry had to be established for greater than 10 years in order to see an increase in soil carbon due to lower turnover rates than in the tropics. In addition, it is unclear whether planting trees in pastures has the same benefit for soil organic carbon content as planting trees in arable fields (Upson et al., 2016). Recent studies in the UK have shown that planting trees on farmland can increase soil infiltration rates (e.g. Marshall et al., 2009). However, these studies were carried out at one site. In addition, it is not clear if similar impacts would be observed in lowland agricultural systems; highlighting the need for further research. Given the long time required to study the development of agroforestry and the complex interactions between crops, animals and trees, calibrated and validated simulation models can significantly contribute to the understanding and quantification of environmental benefits and to forecast the resilience of the systems to the predicted climate change (Cardinael et al., 2018).

Aim and objectives

The major aim of this project is therefore to determine the impact of agroforestry on soil health, in particular its impact on soil carbon storage, soil structure and hydrological properties and delivery of wider ecosystem services.

According to your particular research interests, the studentship could address a combination of the following objectives:

  1. Determine short-term and longer-term impacts of agroforestry on soil health indicators.
  2. Evaluate the impact of different agroforestry types (silvoarable, silvopasture, shelter belts, and hedges) on soil health indicators.
  3. Investigate the effects of distance and depth on soil health indicators in a range of different aged agroforestry plots on different soil types .
  4. Quantify the impact of climate change on carbon cycling in agroforestry systems via process-based modelling of soil processes.

The project will enable significant, timely advancements to be made in understanding the impact of agroforestry on soil health in temperate ecosystems and wider ecosystem services . On-farm tree planting could be included in the new Environment land Management (ELM) scheme being developed by Defra, rewarding farmers for public goods delivered by agroforestry. In order for this to occur considerably more research is needed to quantify these public goods benefits and this project could deliver this. Agroforestry could contribute to the UK’s afforestation targets, carbon budgets for agriculture, and ambitions for healthy soil by 2030.

Training and Research Support

You will join the River Basin Process and Management Research cluster in the School of Geography, a vibrant group of researchers studying the interactions between water, soil, and vegetation in river basins. You will also become a member of Water@Leeeds providing opportunities for interdisciplinary collaborations with researchers across Leeds. Supervision by the CASE partner, Woodlands Trust, will provide training in a wide range of skills relating to woodland conservation and supporting farmers to set up agroforestry systems. You will develop a range of research skills, including experimental design, field sampling, chemical analysis, statistical analysis and data interpretation, academic writing skills and giving presentations. Training will be provided in field/laboratory health and safety procedures, the use of field and analytical equipment and process based modelling. In addition the candidate will develop their understanding of (i) soil properties used to quantify soil health, (ii) soil processes and fluxes related to the cycling and storage of carbon in the soil, (iii) soil hydrology.

Entry Requirements

A good first degree (1st or 2i); Masters degree or equivalent in Environmental Science, Geography, Soil Science, Earth Science or related disciplines.  A keen interest in soil processes and environmental issues and strong analytical/statistical/fieldwork skills are desirable but not essential, as full training will be provided during the PhD.

References

Cardinael, R., Guenet, B., Chevallier, T., Dupraz, C., Cozzi, T. & Chenu, C. 2018. High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – combining experimental and modeling approaches. Biogeosciences, 15, 297-317.

De Stefano, A. and Jacobson, M.G., 2018. Soil carbon sequestration in agroforestry systems: a meta-analysis. Agroforestry Systems, pp.1-15.

Dollinger, J. and Jose, S., 2018. Agroforestry for soil health. Agroforestry Systems, pp.1-7.

Marshall M R, Francis O J, Frogbrook Z L , Jackson B M, McIntyre N, Reynolds B, Solloway I, Wheater S and Chell J (2009) The impact of upland land management on flooding: results from an improved pasture hillslope. Hydrological Processes 23 (3), 464–475.

Lorenz, K. and Lal, R., 2014. Soil organic carbon sequestration in agroforestry systems. A review. Agronomy for Sustainable Development, 34(2), pp.443-454.

Oelbermann, M., Voroney, R.P., Gordon, A.M., 2004. Carbon sequestration in tropical and temperate agroforestry systems: a review with examples from Costa Rica and southern Canada. Agriculture, Ecosystems and Environment 104, 359–377.

Upson, M.A., Burgess, P and Morrison, J.I.L., 2016. Soil carbon changes after establishing woodland and agroforestry trees in a grazed pasture. Geoderma 283 (2016) 10–20

Woodland Trust, 2018. Agroforetry in England https://www.woodlandtrust.org.uk/mediafile/100822604/agroforestry-in-england.pdf