Human and poorly utilised animal excreta could supply 13% of nutrients needed by global crops, scientists estimate
A new scientific assessment has estimated that human excreta and livestock manure that is currently poorly utilised or wasted could together meet roughly 13 percent of the nutrient needs of global crops. The finding, published in a peer, reviewed study, quantifies for the first time at a global scale the fertiliser potential locked in waste streams that are often flushed away, dumped or left to decompose without being returned to farmland. The nutrients in question are the three macronutrients that drive crop growth: nitrogen, phosphorus and potassium, collectively known as NPK. According to the researchers, recovering these nutrients would not replace synthetic fertilisers entirely but could meaningfully offset demand at a time when fertiliser prices, energy costs and supply chain disruptions are straining farmers worldwide.
The context for the study lies in a long, standing paradox in global agriculture. Crops remove nutrients from soil, and those nutrients must be replenished if fields are to remain productive, yet the nutrients embedded in human and animal waste are frequently treated as a disposal problem rather than a resource. In many high, income countries, human excreta is managed through centralised sewerage systems that concentrate nutrients in sludge or discharge them into waterways, contributing to algal blooms and water pollution. In parts of the developing world, by contrast, manure from cattle, poultry and other livestock is often left in fields, burned, or washed away rather than being systematically collected, treated and applied to crops.
The study's core estimate rests on accounting for the total quantities of nitrogen, phosphorus and potassium excreted by humans and livestock, then subtracting the portions already recovered and reused through existing practices such as manuring and composting. What remains is a large, geographically uneven pool of nutrients that is either lost to the environment or only partially captured. The researchers emphasise that the 13 percent figure is an aggregate global estimate and that the recoverable share varies widely by region, depending on farming systems, sanitation infrastructure, livestock density and cultural attitudes towards waste. They also note that nutrient recovery is not simply a matter of collection, since waste must be treated to reduce pathogens and contaminants before it can be safely returned to fields.
Reactions to the findings have been mixed but broadly attentive, reflecting both the promise and the sensitivities involved. Agricultural scientists and circular, economy advocates have pointed out that nutrient recovery from waste aligns with efforts to reduce dependence on mined phosphate rock, which is a finite resource concentrated in a handful of countries, and on energy, intensive synthetic nitrogen production. Critics and some public health experts, meanwhile, caution that untreated excreta can carry disease, causing organisms, heavy metals and pharmaceutical residues, meaning that any large, scale recycling programme would require robust safety standards. Policymakers in several countries have already begun exploring nutrient recovery regulations, though implementation remains uneven and largely confined to pilot projects.
The study fits into a wider global conversation about closing nutrient loops in food systems, an idea that has gained traction as fertiliser affordability and food security have moved up the political agenda. International bodies and researchers have increasingly framed sanitation and agriculture as interconnected rather than separate domains, arguing that what is flushed away in cities could nourish fields in the countryside. The circular nutrient approach is also being discussed in the context of climate goals, since producing synthetic fertiliser is emissions, intensive and improper waste management releases greenhouse gases such as methane and nitrous oxide. At the same time, the scale of the opportunity described in the study underscores how much current infrastructure and policy still treat waste as a liability rather than an asset.
Historically, the reuse of human and animal waste as fertiliser is not a new idea but a return to older practice. For centuries, farmers across Asia and Europe applied night soil and manure to their fields, and urban waste collection systems in some cities were organised around supplying nearby farmland. That tradition faded in the twentieth century as synthetic fertilisers became cheap and abundant after the Green Revolution, and as urban sanitation systems prioritised hygiene and convenience over nutrient recovery. The pendulum has begun to swing back in recent decades, with composting toilets, struvite precipitation from wastewater and biogas digesters emerging as modern techniques for capturing nutrients. The new estimate effectively measures how much potential was abandoned during that transition.
What happens next will depend on whether the estimate translates into investment and policy change. Researchers are expected to refine their models to produce country, level and regional breakdowns, which would help governments identify where nutrient recovery makes the most sense economically and environmentally. Pilot programmes in several countries are already testing the logistics of collecting, treating and distributing recovered nutrients, and their results could inform standards for safety and quality. Whether the 13 percent figure becomes a planning target or remains an academic curiosity will hinge on political will, farmer acceptance and the willingness of consumers to accept food grown with recycled nutrients. For now, the study offers a concrete number to anchor a debate that has often been long on principle and short on quantification.
