Submitted to: Advances in Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 11/20/1996
Publication Date: N/A
Interpretive Summary: Semi-arid regions are very susceptible to a loss in soil quality when farmed because of low crop yield, removal of crop residues for feed or fuel, and frequent fallowing to improve water storage and control weeds. Crop rotation, tillage, addition of manure or fertilizer, and the amount of crop residue returned to the soil influence the level of organic matter in soil. It is important to quantify each effect so we can determine agricultural practices that prevent a deterioration in soil quality. When treated correctly, soil can act as a sink to absorb and tie-up some of the carbon dioxide in the atmosphere and reduce adverse effects of global warming. This study was part of an international effort to identify practices that sequester carbon in soil and help ameliorate increased carbon dioxide in the atmosphere. We analyzed carbon change in soils where experiments with differing crop management treatments have been conducted for 30-65 years. Growing a crop every year, minimizing tillage, and adding fertilizer or manure were very favorable for maintaining soil organic matter. Summerfallowing to increase water storage and crop yield was very detrimental to soil organic matter, and methods need to be developed to decrease its use in semi-arid regions. Returning crop residues to the soil increased carbon storage in soil; thus, removal for feed, fuel, or industrial use is to be discouraged where soil erosion is a problem or fallowing is practiced. It appears possible to maintain soil quality, prevent loss of crop productivity, and sequester carbon in semi-arid regions with the proper agricultural practices.
Technical Abstract: Soil quality is difficult to maintain in cultivated soils of semi-arid regions because of low crop residue production, frequent fallowing, and often excessive wind and water erosion. Identification and quantification of practices that increase soil carbon (C) is necessary to identify management systems that sustain crop production, and improve C sequestration as a means for reducing the effect of global climate changes that may result from increased atmospheric carbon dioxide. We analyzed C change in semi-arid soils of the Pacific northwest where crop management experiments have been conducted for 30 to 65 years. Most systems lost C when crop rotations included summerfallow. Reducing tillage or adding nitrogen fertilizer or manure to increase crop growth decreased soil C loss. Development of crop management criteria to maintain soil quality and achieve maximal C sequestering capability appear possible only if crop residues are returned to soil, erosion is kept below 3 tons per hectare, moldboard plowing is avoided, and summerfallowing reduced to less than one year in five.