Manure beats fertilizer at reshaping soil life long-term
Visscher AM, Ndungu SM, Conz RF, Laub M, Mucheru-Muna MW
Soil Health
If you compost or mulch your garden beds instead of relying on synthetic fertilizer, this two-decade experiment shows you're doing something chemical nitrogen can't: actively rebuilding the community of microbes that keep soil fertile.
Scientists tracked soil health on farms in Kenya for 20 years, comparing plots fed with manure, green leafy mulch, crop leftovers, or plain chemical fertilizer. The manure and plant-based composts consistently changed which bacteria and fungi lived in the soil, even across very different climates and soil types, while chemical fertilizer alone left the microbial community largely unchanged. In the driest, poorest soil, manure caused a 30-fold jump in bacteria that help convert nitrogen into plant-usable forms, showing that organic matter, not synthetic fertilizer, is the real driver of long-term soil health.
Key Findings
Site conditions (climate, soil type) explained the largest share of microbial variation: 30% for bacteria and 28% for fungi.
Farmyard manure significantly affected 65 bacterial genera and achieved 96% classification accuracy for distinguishing fungal communities across sites.
At the driest, most nutrient-poor site, manure caused a 30-fold increase in ammonia-oxidizing bacteria compared to untreated soil, while nitrogen fertilizer alone modestly reduced certain nitrogen-cycling genes.
chevron_right Technical Summary
A 20-year study across Kenyan farms found that adding compost and manure reshapes soil microbial life more powerfully than local climate or soil type, while chemical nitrogen fertilizer alone barely changes the microbial community at all.
Abstract Preview
Original paper
Can Organic Amendments Override Environmental Filtering of Soil Microbiomes? Evidence From 20 Years Old Agricultural Field Trials in Contrasting Tropical Sites.
Soil microbial communities underpin ecosystem functions critical for sustainable agriculture, yet our understanding of how long-term management of tropical agroecosystems shapes these communities r...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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