Tuesday, November 14, 2006

Evaluation of Mehlich Buffer as an Alternative to the Woodruff Buffer for Lime Recommendations in Missouri.

Manjula Nathan1, Peter Scharf2, and Yichang Sun2. (1) University of Missouri, University of Missouri, 23 Mumford Hall, Columbia, MO 65211, (2) Univ of Missouri, 108 Waters Hall, Columbia, MO 65211

In Missouri, the Modified Woodruff Buffer (MWB) test is used to determine the lime requirement in soils. Though this method has proven to work for Missouri soils it uses para-nitrophenol as one of the reagents which is a hazardous substance. Also, since Missouri is the only state in the nation which uses the Woodruff Buffer test, it is better to evaluate the other buffer tests used so that data and lime recommendations developed for Missouri can be compared with similar information from the other states. Recent studies conducted in Maine, Pennsylvania and Virginia found the Modified Mehlich Buffer (MMB) test to be a better method for determining lime requirement in soils. Therefore, laboratory incubation studies were conducted to evaluate MMB as an alternative to MWB for determining lime recommendations for Missouri soils. Twenty soil samples collected from different soil regions in Missouri that represent major agricultural areas were used in the soil incubation study. Lime requirement in the soils selected for incubation study was estimated by the MWB test and the MMB test method. Soils were amended with reagent grade CaCO3 at rates of 0, 1/3, 2/3, 1 and 1 1/3 and 2 times the estimated lime requirement from the MWB method to raise the soil pHs for target of 5.5-6.0, 6.0 -6.5, and 6.5 -7.0 ranges, and incubated in the dark for a total duration of three months, with a three weeks interval wetting and drying cycle. Soil pH was regressed with CaCO3 added to all 20 soils, and the actual lime requirement was estimated for each soil to raise the soil pH to target levels of 5.8, 6.3 and 6.8. MWB and MMB pHs were regressed against actual lime requirement for all 20 soils to evaluate effectiveness of each test for estimating the lime requirement in Missouri soils.