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The Profitability of Variable Rate Lime in Wheat
B. Mills, B. Brorsen, D. Arnall
B.E. Mills and B.W. Brorsen, Dep. of Agricultural Economics, Oklahoma State Univ., and D.B. Arnall Dep. of Plant and Soil Science, Oklahoma State Univ., Stillwater, OK 74078

Grid sampling allows a variable rate of lime to be applied and has been marketed as a cost saver to producers. However, there is little research that shows if this precision application is profitable or not. Previous research on variable-rate lime has considered only a small number of fields. This paper uses soil sampling data from 170 fields provided by producers in Oklahoma and Kansas. We compare net returns of variable rate to uniform rate lime for grain only wheat production, dual-purpose wheat grain and forage production, and a wheat-soybean rotation. Using university lime rate recommendation tables, we calculated the lime rate for variable rate using grid sampling and uniform rate using an estimated composite sample. We then calculated expected yield over a five year period to estimate the difference in net returns from variable rate lime for the three production systems. We evaluated a range of target pHs from 6.0 to 6.9. On average, net revenues were maximized at a target pH of 6.5 for variable and uniform rates. At this level, variable rate averaged $3.42/acre less net returns for grain only and $8.56/acre less with dual-purpose. For grain only, 66 of the 170 fields had higher net returns for variable rate at the optimal target pH. In a dual-purpose system only 32 of the 170 fields had higher net returns with a variable rate. For a wheat-soybean rotation at the optimal target pH of 6.5, variable rate had $6.02/acre higher average net returns than a uniform rate. Thus, variable rate liming is a marginal investment, but there are times when it can pay.

Keyword: Wheat, Lime, Precision Agriculture, Variable Rate, Profitability