BIOLOGICAL RECYCLING OF SOIL NUTRIENTS
Sustainable Agriculture
James Hoorman
Assistant Professor
Ohio State University Extension
Ottawa
Abstract
The objective was to compare field decomposition of various cover crops (6 legumes, 4 grasses) residues under no-till conditions using a randomized complete design with 3 replications. A 200 g composite fresh aboveground sample from each replicated plot was taken in 4 nylon mesh bags and placed in close contact with the field soil. Mesh bags were collected from the field every 3 months for four years, weighted, and oven-dried for temporal loss of residues. On average, a significantly greater decomposition of residues was found for winter pea (>89%) and lower decomposition rates for spelt (52%) and Sudan-sorghum grass (46%) residues. Within first 3 months, significantly greater decomposition was found for Clover, winter peas, Cowpeas, Hairy vetch than Ryegrass, coriander, spelt, and Sudan-sorghum grass residues, respectively. However, net difference in residue decomposition between 3 and 6 months was higher for coriander and clover than spelt and Sudan-sorghum grass. Cowpeas, Hairy vetch, and winter pea residues decomposition were significantly higher than Sudan-sorghum grass. The net difference in residue decomposition between 6 and 9 months was highest for ryegrass and lowest for clover. On average, leguminous cover crops had a faster and higher decomposition rates than grasses used as cover crops. Results suggest that field decomposition of cover crop residues depends on C:N ratios, soil temperature and amount of rainfall. Organic residues with a low C:N ratio (<20) decompose quickly and nutrients are released quickly (4 to 8 weeks) while high C:N ratio (>20) residues decompose slowly and tie up soil N.
Authors: Hoorman, J.
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Hoorman, J. Extension Educator, Cover Crops & Water Quality, Ohio State University Extension, Ohio, 45841