Mr. Joseph Wilson - Master of Soil Science Student

Mr. Joseph Wilson Master of Soil Science Student Department of Crop and Soil Sciences Committee: David Hardy (co-advisor), John Havlin (co-advisor), Carl Crozier, and David Jordan Moderator: Chandler Fulmer, MS Student in Soil Science Field and Laboratory Evaluations of NCDA Lime Recommendations Over the last four years, the NCDA&CS Soil Testing Laboratory changed its soil:water pH (pHW) method to soil:0.01 M CaCl2 solution (pHS) and is reporting an adjusted water pH (pHadjW) by increasing pHS by 0.6 units. Also, a modified Mehlich soil buffer pH (BpH) method replaced the original Mehlich buffer to measure exchangeable acidity (Ac). Currently, lime requirement (LR) is calculated as: lime (t/ac) = × [( − !"#$)⁄(6.6 − !"#$)]. Due to these significant changes, field and laboratory studies were conducted to evaluate the current LR method’s ability to achieve target pH on North Carolina soils. Comparisons prior to change and substituting pHS for pHadjW were made. The University of Georgia LR method was also evaluated. Four, two-year field studies were established with eight treatments: four multiples of the NCDA LR (0X, 1X, 2X, 4X) in two tillage systems (till, no-till). Incorporated treatments were rototilled twice to 10 cm. Soil samples were collected at three depths (0-10 cm, 10-20 cm, 20-30 cm) every four months in the first year and every six months the second year. Eleven soils varying in texture and organic matter were collected for a six-month lime incubation including five multiples of the NCDA LR (0X, 0.5X, 1X, 1.5X, 2X). Soils were sampled every month. Soil from each of the four field sites was included in the incubation study for laboratory to field comparisons. All soil samples were analyzed for pHW, pHS, and BpH. Incubation and field results indicate that NCDA LRs were more accurate than the previous method, but under-recommend lime by an average factor of two for incorporated lime in finer textured soils. Field results further show NCDA LRs require an average multiplier of three to reach target pH in no-till systems. Further research involving a larger population of soils is warranted.