title: Opposing effects of different soil organic matter fractions on crop yields.
abstract: Soil organic matter is critical to sustainable agriculture because it provides nutrients to crops as it decomposes and increases nutrient- and water-holding capacity when built up. Fast- and slow-cycling fractions of soil organic matter can have different impacts on crop production because fast-cycling fractions rapidly release nutrients for short-term plant growth and slow-cycling fractions bind nutrients that mineralize slowly and build up water-holding capacity. We explored the controls on these fractions in a tropical agroecosystem and their relationship to crop yields. We performed physical fractionation of soil organic matter from 48 farms and plots in western Kenya. We found that fast-cycling, particulate organic matter was positively related to crop yields, but did not have a strong effect, while slower-cycling, mineral-associated organic matter was negatively related to yields. Our finding that slower-cycling organic matter was negatively related to yield points to a need to revise the view that stabilization of organic matter positively impacts food security. Our results support a new paradigm that different soil organic matter fractions are controlled by different mechanisms, potentially leading to different relationships with management outcomes, like crop yield. Effectively managing soils for sustainable agriculture requires quantifying the effects of specific organic matter fractions on these outcomes.
authors.affiliation: Department of Ecology, Evolution & Environmental Biology, Columbia University, 1200 Amsterdam Ave., 10th Fl., New York, New York, 10027, USA. stephen.wood@yale.edu.|Agriculture and Food Security Center, The Earth Institute at Columbia University, 61 Route 9W, Lamont Hall, 2G, New York, New York, 10964, USA. stephen.wood@yale.edu.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Wood
authors.affiliation: School of Forestry and Environmental Studies, Yale University, 195 Prospect St., New Haven, Connecticut, 06511, USA.
authors.forename: Noah
authors.initials: N
authors.lastname: Sokol
authors.affiliation: Natural Resource Ecology Laboratory, Colorado State University, 1499 Campus Delivery, Fort Collins, Colorado, 80523, USA.
authors.forename: Colin W
authors.initials: CW
authors.lastname: Bell
authors.affiliation: School of Forestry and Environmental Studies, Yale University, 195 Prospect St., New Haven, Connecticut, 06511, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Bradford
authors.affiliation: Department of Ecology, Evolution & Environmental Biology, Columbia University, 1200 Amsterdam Ave., 10th Fl., New York, New York, 10027, USA.
authors.forename: Shahid
authors.initials: S
authors.lastname: Naeem
authors.affiliation: Natural Resource Ecology Laboratory, Colorado State University, 1499 Campus Delivery, Fort Collins, Colorado, 80523, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Wallenstein
authors.affiliation: Agriculture and Food Security Center, The Earth Institute at Columbia University, 61 Route 9W, Lamont Hall, 2G, New York, New York, 10964, USA.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Palm
mesh_terms: D000349:Africa; D000383:Agriculture; D002244:Carbon; D018556:Crops, Agricultural / Q000254:growth & development*; D004784:Environmental Monitoring; D009584:Nitrogen; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen
keywords: Africa; agroforestry; carbon; extracellular enzymes; legumes; microbes; soil organic matter