Submitted to: Direct Seeding Intensive Cropping Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/18/2001
Publication Date: N/A
Technical Abstract: Data from long-term experiments ongoing at CPCRC, Pendleton OR, show that most traditional dryland farming methods result in a reduction in soil organic matter content from the original native grasslands. Wheat/fallow crop rotations lose the most, wheat/pea loses less, and annual wheat loses the least organic matter on an annual basis. Tillage is a second factor in the rate of soil organic matter loss. Increased tillage intensity, related to depth of disturbance and how completely surface residues are mixed with soil and place below the surface, increases the rate of soil organic matter loss. Long-term trends indicate that each crop rotation is headed toward a specific equilibrium soil organic matter level determined by residue input and tillage intensity. Systems which accumulate relatively high soil organic matter levels also have larger proportions of unstable, more easily decomposed organic matter. Measuring changes in soil organic matter is difficult because it take decades for measurable changes to occur, current measurement techniques include variable amounts of recently deposited residues, and variability within fields and between sampling techniques is significant. Cropping systems which minimize tillage cause soil quality effects not related to an increase in total soil organic matter content, such as stratification of high organic matter near the soil surface where it has a greater effect on tilth, infiltration, and other soil properties.