Graduate Thesis Or Dissertation
 

Effects of ryegrass residue management on Dayton soil organic carbon content, distribution and related properties

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  • Total organic carbon, total nitrogen, microbial respiration and enzyme activity (β-glucosidase) were measured on several horizons of a Dayton silt loam (fine, montmorillonitic, mesic, Typic Albaqualf) soil cropped to annual ryegrass under two straw residue management systems. The study evaluated the effects of annual burning of straw residues or annual incorporation of straw residues on the content, distribution and bioavailability of soil organic carbon. Four fields were selected to represent the burn management system which have been annually burned for a minimum of 40 years. Four fields were selected to represent the straw incorportated system (mold board plow) which had been annually burned for approximately 30 years, followed by incorporation of straw residues into soil for a minimum of 10 years. One native site was selected to represent non-cultivation conditions. Straw management system strongly influenced both the total organic C and N and microbial activity the surface soil horizon. Soil organic C and N content were significantly greater (p < 0.05) in the Ap horizons of soils under the plowed management system than soils under the burned management system. The collective evidence suggests, however, that the significant differences observed between the two residue management systems are not due to greater losses of soil organic C and N as a result of burning but rather that organic C levels have increased as a result of a change in management. Soil C:N ratios are slightly higher in the Ap horizons of soils as a result of straw residue incorporation in comparison to burning of straw residues. When expressed on a mass soil basis, both C0₂ evolution from microbial respiration, during a 32 day incubation period, and enzyme activity were significantly greater (p < 0.10) for the Ap horizon of soils where straw residue had been incorporated than in soils where residues had been annually burned. When expressed on a per gram C basis, neither C0₂ evolution from microbial respiration or enzyme activity were significantly different between the two management systems. These results indicate that long-term annual burning of straw residues has not decreased the bioavailability of soil organic C.
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