Soil Carbon, Nitrogen Pools and Cycling Efficiencies in Organic vs. Conventional Systems. (A08-harwood212446-oral)
Authors:
R.R. Harwood* - Michigan State University J.E. Sanchez - Oklahoma State University J. Smeenk - Michigan State University
A.F. Fortuna - U.S. Department of Agriculture E.A. Paul - Colorado State University
Abstract:
Evidence on the dynamics of C and N pools comparing organic with a range of alternative crop management strategies was taken from a series of closely-related long term studies conducted in Michigan from 1993 to 2000. We found that pool sizes change across rotations, tillage types and between fertility treatments in patters that are consistent over time and locations. Organic rotations of corn, wheat and soybeans with compost application showed the greatest N mineralization potential when cover crops were used, reaching a maximum of 112 mg/kg of soil in the top 15 cm after six years.
The mineralizable N pool was highly correlated with the carbon pool, with no values in any treatment, organic or conventional, exceeding 60 mg N/kg of soil without at least 1000mg/kg of mineralizable C.
Organic systems with rotation were significantly higher in short term pools of both C and N than were continuous corn conventional systems that received higher inputs of both C and N over the 6 year period. Diverse-crop organic systems have the potential to accumulate higher levels of both C and N as long as tillage remains limited to chisel plowing or other, even less aggressive types. short-term pools of both C and N are sharply reduced by moldboard plowing. The C and N data are consistent with results from microbial biomass and nematode population structure measurements.
Speaker Information: Richard Harwood, Michigan State University, 5992 Wynn Jones Rd., Port Orchard, WA 98366; Phone: 360-871-4292; E-mail: [email protected]
Session Information: Wednesday, November 5, 2003, 7:30 AM-11:00 AM Presentation Start: 9:40 AM
Keywords: Organic Agriculture; Cropping Systems; Nitrogen Pools; Carbon Pools
