Field Calibration and Lab Evaluation of BufferTests for Determining Lime Requirement in Missouri Soils.

The Modified Woodruff Buffer (MWB) test is used to determine lime requirement (LR) for Missouri soils. Though this method is proven to work for Missouri soils, it uses p-nitrophenol which is a hazardous substance.  Soil testing labs are under increasing pressure to reduce hazardous wastes which must be collected and disposed of following USEPA protocols. The goal of this study was to evaluate the Modified Mehlich Buffer (MMB) and the Sikora Buffer (SB) as alternatives to the MWB in determining the LR for Missouri soils.  Thirty soils were collected from major agricultural areas in Missouri, treated with calcium carbonate (CaCO3), and incubated for 90 d. Soil pHs (0.01 M CaCl2 1:1) was regressed against CaCO3 rate, and actual LR was estimated for each soil to raise the soil pHs to target levels of 5.8, 6.3 and 6.8. The MMB and SBs were found to be as good as MWB in predicting LR in Missouri soils. A field calibration study was established at University of Missouri Bradford (BF), Greenley (GR), Southwest (SW), Delta (DL) and Hundley-Whaley (HW) Research and Extension Centers. The BF, DE, GR and HW sites were planted with corn-soybean rotations; SW site was planted with tall-fescue. Each sites received seven lime treatments to cover a wide range from low, recommended LR, and 2xLR lime rates. The experiment was in a randomized complete block design with four replicates. Soil samples were collected (0 to 15-cm) at the beginning and at 45d, 90d, 120d and 360d after lime applications and analyzed for pHs, and for buffer pH using MWB, MMB and SBs. The crop yield data was collected at all five sites. Results from the field calibration and the lab incubation studies will be presented.