SOIL SAMPLING PROCEDURES FOR MONITORING POTASSIUM DISTRIBUTION IN GRAZED PASTURES

Nutrient redistribution in grazed pastures occurs primarily via deposition of excreta by animals. Because this redistribution is generally not uniform, a composite sample of randomly collected soil cores may not reflect the nutrient status of much of the pasture. To address this limitation, zonal soil sampling, with zones determined by distance from shade, water, and supplemental feeders (lounging areas), has been proposed as an alternative sampling strategy. This experiment was conducted to evaluate the potential of zonal soil sampling for monitoring extractable K distribution in grazed pastures. Utility of the zonal approach was evaluated by comparing it with a more rigorous, but less practical transect sampling procedure. Rotationally and continuously stocked bermudagrass [Cynodon dactylon (L.) Pers. 'Callie'] pastures were used in the study. Ranges of extractable K within a pasture were as great as 13-fold (14-181 mg kg-1) after 2 yr of grazing. Extractable K concentration was greatest in the one-third of the pastures closest to lounging areas regardless of grazing method. Data from zonal soil sampling described this distribution of soil K. Kriged contour maps constructed using data from transect soil sampling supported the conclusions made using zonal sampling. We conclude that zonal soil sampling is a useful and practical tool for describing K redistribution in pastures and for improving the utility of soil test results and ferlilizer recommendations for grazed swards.