Subsoil ridge tillage and lime effects on soil microbial activity, soil pH, erosion, and wheat and pea yield in the Pacific Northwest, USA

Soil erosion and the gradual acidification of soils are two major obstacles limiting crop productivity in the Palouse region of eastern Washington and northern Idaho. New tillage practices that replace the traditional moldboard plow are needed to maintain more surface cover to reduce erosion. Two tillage systems and lime were compared at two locations on silt loam soils. Treatment combinations were two levels of tillage (subsoil ridge till (SSRT) and plowing) and two levels of lime (0 and 2.68 Mg ha(-1)). Crop rotations were barley (Hordeum vulgare L.)-pea (Pisum sativum L.)-wheat (Triticum aestivum L.) at both sites in the US that receive 500-560 mm precipitation annually. Tillage and lime options were implemented after barley stubble and studied for 2 years. Microbial biomass, respiration, and dehydrogenase enzyme activity were enhanced at the Washington site under SSRT because of the initially higher residue levels and because residues were maintained at or near the soil surface compared to plowing. Liming increased soil pH and respiration and maintained microbial biomass at about 100 ug C g(-1) higher than for the unlimed plots at the end of 2 years. Soil moisture increased under SSRT at some profile depths. Pea seed yield at the Washington site and wheat yield at the Idaho site were significantly higher for SSRT compared to plowing. Lime significantly increased wheat yield only at the Washington site. Significantly higher surface residue was maintained during the study period from SSRT compared to plowing which contributed to lower rates of soil erosion in winter wheat 30 months after plot establishment. At the Washington site, surface residue levels were 20% in spring of 1992 for SSRT compared to less than 1% for plowing. One year later, soil erosion under winter wheat in spring of 1993 was 1.3 Mg ha(-1) for SSRT compared to 8.4 Mg ha(-1) for plowing. In general, the higher surface residue maintained under SSRT increased microbial activity, maintained higher surface residue, and reduced erosion in winter wheat, the vulnerable phase in the crop rotation for erosion. (C) 2003 Elsevier Science B.V. All rights reserved.