Wednesday, November 15, 2006

Soil Acidity and Lime Responses in the Pacific Northwest.

Paul Carter1, Tabitha Brown1, Lyndon Porter2, David Huggins3, Donald Wysocki4, and Richard Koenig1. (1) Washington State Univ, 202 S 2nd St, Dayton, WA 99328, (2) USDA-ARS, Vegetable and Forage Crop Research Unit, IAREC, 24106 N Bunn Rd, Prosser, WA 99350-8694, (3) USDA-ARS, Washington State Univ, 215 Johnson Hall, Pullman, WA 99164, (4) Columbia Basin Ag Research Center, Columbia Basin Agric.Res.Ctr., PO Box 370, Pendleton, OR 97801

Soil quality and conservation is improved with minimum or no-tillage farming practices. Soils of the Palouse region of Washington, Oregon, and Idaho have developed stratified layers of acidity when tillage is reduced or eliminated. Some soil pHs have become relatively acidic (<5.0) in the upper 15 cm; however, it is not known whether this acid layer is impacting crop yields. The objective of this research was to determine the influence of lime rate on wheat, pea, and other rotational crop yields and, if necessary, to develop lime recommendations for cropping systems in the Palouse region. On-farm trials were established in fields under continuous no-till or reduced-tillage cropping. Treatments include a non-treated control, elemental sulfur application at 2,240 kg/ha, and applications of pelletized lime at rates of 2,240 to 11,200 kg/ha. Soil samples were collected at depths of 0 to15 cm and 15 to 30 cm, and in 1-cm increment to a depth of 15 cm to characterize initial soil pH conditions.  Initial soil pH (0 to 15-cm depth) ranged from 4.9 to 5.6. Detailed (1 cm increment) sampling indicated an acidic band at the 2 to 8 cm depth at no-till locations.  Soil pH in this acidic band is as low as 3.9 at some locations. Even though soil pH is below critical levels, wheat and pea yield responses to lime have been inconsistent, perhaps due to higher organic matter levels in reduced tillage systems.