Nutrient circularity in African livestock systems

The individual components of an agroecosystem (the soils, plants, and animals) are linked through the nutrients that cycle through them. Plants grow on soils that provide nutrients such as nitrogen and phosphorus, which the plants take up and store in their biomass, thereby producing crop harvests and feeds and forages for livestock. Livestock feed on those plants, either directly while grazing on grasslands, pastures, or crop residues, or through cut-and-carry where fodder is provided in feeding troughs. Some of the nutrients from the plant are then converted into livestock products (milk, meat, eggs), while the largest fraction of nutrients is excreted in the form of animal manure. This manure is either deposited directly on the land while grazing, or it can be collected from animal housing, stored, and applied back on the croplands and grazing lands, thereby returning nutrients to the soil and closing the cycle. 

But these nutrient cycles are often imperfect and “leaky”, meaning that nutrients can be lost along the way. For example, manure nutrients can be leached into the ground as nitrate and phosphate, where they cause groundwater pollution and eutrophication, they can be lost through volatilization of ammonia, which is an air pollutant, or they can be emitted as greenhouse gases methane and nitrous oxide, which are harmful for the climate. Nutrients are also lost when livestock feeds are spoilt, for example due to improper storage of hay or crop residues, or when fertilizer is applied to croplands at improper quantities or times (too much at the wrong time). In addition to environmental externalities, losing nutrients is severely undermining productivity in African agroecosystems that are already nutrient-limited. 

 At ILRI’s Mazingira Centre, our aim is (i) to better understand nutrient cycling processes in African smallholder and pastoral systems, (ii) to identify the most important pathways of nutrient loss, and (iii) to develop and test interventions to increase nutrient circularity. Through the scientific evidence we create, we develop guidelines for improved circular nutrient management, which has several benefits:

• Healthier soils through the protection of soil organic matter, which provides erosion control, improves drought resilience through better water-holding capacity, and protects soil carbon storage;
• Healthier vegetation, leading to higher biomass productivity and better nutritional quality, as well as protection of biodiversity through proper grassland management;
• Healthier animals through improved feeding and by considering aspects of animal health (e.g., reduced pathogen loads, reduced AMR) in manure management recommendations;
• Healthier environments by improving livestock system sustainability;
• All of which lead to higher productivity in livestock systems.

• We linked maize yield gaps caused by N limitation to soil N2O emissions in sub-Saharan Africa at the continental scale (Leitner et al., 2020).
• We developed a full nitrogen budget for ILRI’s Kapiti Research Station as an example for an extensive rangeland (Carbonell et al, 2021).
• We showed that the decomposition rate and with that the nutrient release of livestock manure in semi-arid drylands is water limited and much slower than in temperate regions (Zhu et al., 2020).
• We described the main nitrogen cycling processes leading to N2O formation in cattle bomas using functional gene analysis and stable isotope measurements (Fang et al., 2024)
• We described soil microbial communities in a paddy rice field in Kenya (Gorfer et al.; 2022).
• We’ve created an interactive soil map of the Kapiti Research Station and Wildlife Conservancy as foundation for research on grassland restoration and nutrient cycling.
• We described the main uncertainties in nitrogen budgets for smallholder African livestock systems (Rufino et al., 2014).
• We showed that pasture enclosures can increase pasture production and soil organic carbon in semi-arid rangelands (Oduor et al., 2018).