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Inga agroforestry to enhance soil regeneration and carbon sequestration in degraded tropical soils.


   School of Agriculture, Policy and Development

  Prof M Lukac, , Ms Nicola Peel  Applications accepted all year round  Self-Funded PhD Students Only

About the Project

Extensive tracts of land in the tropics have already been cleared of forest, used first to grow crops and then as pasture. The removal of the tropical forest severely diminishes the capacity of the ecosystem to retain nutrients and carbon in the soil. As the soils get exhausted, new parcels of forest need to be brought under cultivation to maintain food production. Clearly, reforestation is the preferred solution, however dense trees do tend to get in the way of agriculture.

This PhD will focus on a promising land-use type that is increasingly gaining prominence: agroforestry. Agroforestry allows farmers to continue producing food while significantly improving the environmental sustainability of their operations by integrating trees with their farm systems. The purposeful integration of trees and crops within the same parcel of land is exceptionally versatile and varied. Agroforestry has an in-built capacity to evolve local variations emphasising different land quality, climate and ecological sensitivity, and agricultural traditions.

In recent years, there has been significant interest in the use of Inga as the tree species of choice in agroforestry subsistence farming. Inga trees, which are native to the Amazon, are typically planted in rows while crop production continues in alleys between the tree rows. We have anecdotal evidence of a considerable soil recovery and yield benefit to crops grown under the Inga. This PhD aims to place this patchy evidence on a scientific footing by describing the environmental benefits of Inga agroforestry in Ecuador. We will use the established network of small-holder farmers where Inga agroforestry is already practiced to investigate the functionality and the sustainability of Inga agroforestry systems – with a strong focus on the soil.

Agroforestry systems can deliver to multiple objectives: carbon capture, landscape sustainability, food production and income generation. The challenge for this PhD is to generate empirical evidence of these benefits and communicate them to the farmers to influence their decision making. The core objective is to describe the stimulation of soil recovery by Inga alleys. We will measure carbon deposition and transformations in the soil, describe soil biota and investigate the availability of macronutrients to crops. We will compare these measurement with data obtained from conventional arable systems to show the benefit of Inga integration. This PhD will also look at the potential of generating biochar from Inga wood harvested during tree management. Biochar added to the soil has been shown to act as a nutrient sponge – absorbing excess capacity for slow release later, and as a long-term carbon storage option. The fieldwork aims to generate a dataset describing nutrient retention and the capacity to sequester carbon of Inga agroforestry.

Rainforest Saver, who support this PhD, has a network of 38 farms in Ecuador where Inga agroforestry has already been practiced for various lengths of time. The farmers are engaged in citizen science and collect data, this resource will be available to the PhD student. In a final step, the datasets generated by this PhD research and the citizen science observations will be used to adapt existing agroforestry models (SustainFarm, FarmTreeTool) to Inga agroforestry – we do not currently the capability to model ecosystem services and management in Inga agroforestry.

Ultimately, the outcome of this PhD will be a novel understanding of Inga agroforestry systems and their role in improving the sustainability of tropical agriculture. The PhD will generate scientific evidence of the potential of Inga trees to improve farmer livelihoods and lower the environmental impact of food production by enhancing the recovery of soils in the tropics.

Student profile:

This PhD will suit a student with a background in plant ecology, environmental sciences, or agriculture. Students with knowledge of ecosystem modelling, soil science and plant-soil relationships would be particularly well placed. Understanding tropical agriculture or forestry is an advantage, as is knowledge of statistical analyses, scripting/programming, and an ability to speak Spanish. The skills required are broad, existing skills and interests will guide the direction in which the student takes the PhD. 


Funding Notes

Please note there is no funding associated with this project.

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