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ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #148715
Title: SOIL CARBON TRENDS IN PACIFIC NORTHWEST WHEAT-FALLOW SYSTEMS

Author
item Albrecht, Stephan
item MACHADO, STEPHEN - OREGON STATE UNIV.
item Wilkins, Dale

Submitted to: Columbia Basin Agricultural Research Annual Report
Publication Type: Other
Publication Acceptance Date: 3/3/2003
Publication Date: 6/1/2003
Citation: ALBRECHT, S.L., MACHADO, S., WILKINS, D.E. SOIL CARBON TRENDS IN PACIFIC NORTHWEST WHEAT-FALLOW SYSTEMS. COLUMBIA BASIN AGRICULTURAL RESEARCH ANNUAL REPORT. 2003.

Interpretive Summary: In the cereal-producing, dryland region of the Columbia Basin in the Pacific Northwest, the summer rainfall is insufficient for most crops. However, the area is well suited for winter annuals such as wheat. Although winter wheat yields in the region have increased since the area was opened to farming, soil quality, especially soil organic matter, has continued to decline when summer fallow is included in the management system. Summer fallow is the practice of allowing the ground to lie fallow for one year, then growing a crop the second year, hence producing one crop with two years of rainfall. In the 1930s, several long-term experiments were started at the Pendleton Experiment Station in northeastern Oregon to evaluate the effects of fertilizer, residue management, and tillage on crop productivity. Soil carbon determinations from two long-term experiments; one in summer fallow, the other a pasture, and each seventy years old; were evaluated. Soil carbon determinations provide an estimate of soil organic matter content and thus soil quality. Soil carbon declined in all experimental plots that were plowed and utilized summer fallow, except when substantial organic amendments, such as manure, were applied. Nitrogen fertilization eased soil carbon loss; however, the practice of burning wheat residue accelerated soil carbon loss. Manure applications increased soil carbon in the upper soil layers, but even with the manure additions, soil carbon below 12 inches declined with time. It was found that in an undisturbed grass pasture, soil carbon in the topsoil showed a substantial increase. This study strongly suggests that the fallow management system degrades soil carbon and soil quality.

Technical Abstract: In the Columbia Basin summer rainfall is inadequate for warm season crops, but the area is well suited for winter annuals and cool-season grasses. Although winter wheat yields in the region have increased over time, soil carbon and organic matter have continued to decline under the winter wheat/summer fallow rotation common in this area - even where soil erosion is minimal. In the 1930s, several long-term experiments were started at the Pendleton Experiment Station in northeastern Oregon to evaluate the effects of fertilizer, residue management, and tillage on crop productivity in the cereal-producing, dryland regions of the Columbia Basin. A chronosequence of soil carbon determinations from the long-term experiments were evaluated. Soil carbon declined in all conventional management systems, except when substantial organic amendments were applied. Nitrogen fertilization reduced the soil carbon decrease; however, residue burning intensified soil carbon loss. Manure applications increased soil carbon in the upper depths; however, even with manure additions, soil carbon below 12 in declined with time. Soil carbon in the upper 12 in increased substantially under a grass pasture management. It can be concluded that the wheat/fallow system is very detrimental to maintaining soil carbon.