Published in the journal Nature Food, the research could help policymakers to factor excreta into their planning for more sustainable food production systems, and increase confidence in the use of human excreta, in the form of faecal sludge, to supplement manufactured fertilisers.
The study, led by the University of Leeds and the International Water Management Institute (IWMI), looked at 253 crop fields in Ethiopia, Kenya, India and Bangladesh, and compared yields and soil fertility across fields that did or did not receive excreta.
The researchers found that the application of excreta increased crop yields on average by 25%, and total nutrient uptake by 34%. This was mainly because of increases in nitrogen and phosphorus, which are essential for plant growth.
They also found that excreta reduced the need for chemical fertilisers by an average of 44%, and could therefore help to reduce chemical pollution and greenhouse gas emissions associated with fertiliser production.
Dr Beth Greenhough, from the School of Earth and Environment at Leeds and lead author of the study, said: “Our findings suggest that the use of human excreta as a fertiliser has the potential to significantly increase crop production, reduce chemical fertiliser use and protect the environment.
“However, this needs to be done carefully, with adequate treatment of the excreta to remove pathogens and pollutants.”
Dr Manzoor Qadir, from the IWMI, said: “With careful management, human excreta can be an important source of nutrients for crops and help to improve soil fertility. Our research provides evidence to support the safe use of excreta in agriculture.”
The study was funded by the UK Natural Environment Research Council (NERC) and the CGIAR Research Program on Water, Land and Ecosystems.
Read the full paper: Greenhough, B. et al. (2023) Crop yield and soil fertility responses to human excreta application in South and South East Asia and sub-Saharan Africa: a systematic review and meta-analysis. *Nature Food*. DOI: 10.1038/s43016-023-00914-0.
