The Efficacy of Soil Sampling Methods for Kentucky Soils.

The collection of soil data can be obtained by using a variety of methods. The methods examined in this study will focus on grid sampling, composite sampling and zone sampling. The objective of this study was to determine the efficacy of three specific soil sampling methods with the intent of making the most accurate variable rate fertilizer application. Samples were collected from 2 counties in Kentucky: Jefferson and Calloway. Each field was grid sampled using a 0.25 acre grid. P and K levels were determined using the Mehlich III method. The results of the soil test analyses were used to determine the amount of P and K fertilizers that should be applied to each field in order to provide the needed nutrients for a soybean crop with a yield of 40 bushels per acre. The soil test analysis results were integrated into multiple fertilizer recommendation equations to analyze the significance of the results. Nutrient variation throughout all of the fields was significant. Coefficient of variation was calculated to determine the significance of the variability for each field and each sampling approach. Based on preliminary analyses of the coefficient of variation of nutrients within a field and the corresponding fertilizer recommendation, grid sampling results in the most accurate fertilizer application of the three methods examined in this study.