Saturday, 15 July 2006

Corn Residue Incorporation and Manure Application History Influence Soil Enzyme Activities and Inorganic Nitrogen Dynamic.

Farshid Nourbakhsh1, Nazila Khorsandi1, and Richard Dick2. (1) Isfahan Univ of Technology, 84154, Isfahan, 84154, Iran, (2) Ohio State Univ, School of Natural Resources, 2021 Coffey Road, Columbus, OH 43210-1085

Soil organic matter is an active component of agroecosystems. Corn residues are generally considered as poor-N, low quality plant materials. A laboratory experiment was conducted to investigate the effects of corn residue application on the inorganic N dynamics and soil enzyme activities under different manure fertilization history. Nine soil samples were taken from three replications of control, 50 Mg ha-1year-1 and 100 Mg ha-1 year-1 treatments. The laboratory experiment was a factorial of the three fertilization history and the three residue applications including control (with no residue application), corn shoots and corn roots (at 1 g C kg-1 soil). Inorganic N was monitored by destructive sampling during 20 weeks of incubation at 10 occasions: 0, 1, 2, 4, 6, 8, 10, 13, 16 and 20 weeks. urease, L-asparaginase, L-glutaminase and - glucosidase activities were measured at two occasions 0 and 20 weeks. Results indicated that the treatments with no application of residues showed a flash of inorganic N during the first week of incubation followed by a slower inorganic N release phase. Regardless of the manure application history, similar patterns were observed in inorganic N accumulation with time. The treatments with no corn residue application did not show N immobilization. Inorganic N declined drastically in the corn residue-applied treatments in the first 2 weeks of incubation, followed by gradual release of inorganic N during the next 18 weeks. Urease, L-asparaginase, L-glutaminase and - glucosidase activities at the end of incubation were poorly influenced by the residue application. In contrast, the enzyme activities were significantly increased by increasing manure application rates. Overall, we concluded that, N immobilization occurred in corn-root and -shoot applied soils regardless of the fertilization history. However, the final concentrations of inorganic N in soil depended on the total amounts of manure N applied to soil.

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