Determining fungicide rates for soils old and new

Tifway bermudagrass growing on renovated soil (left) and existing topsoil (right). The greater quantity of nutrients in the existing topsoil resulted in acceptable turfgrass, whereas the newly renovated turfgrass growing on poor soil on the left required more nitrogen.

Superintendents often follow best management practices (BMPs) for establishing turfgrass, which provide a range of nutrient applications that have been determined to be sufficient. However, many BMPs do not account for differences that may exist due to soils or nutrient sources. Two superintendents may follow the same nitrogen recommendation; one develops high-quality fairways, the other does not. To address this problem, we are determining if current nutrient recommendations are sufficient for both existing and newly renovated soils.

The study began by simulating the same methods of fairway construction. In half of the research plots, topsoil was removed and replaced with the underlying subsoil. In the remaining plots, the topsoil remained intact. We applied nitrogen to each of these soils, either soluble urea or as polymer-coated urea. First-year results indicate bermudagrass grown on newly renovated soils requires an amount of nitrogen greater than the highest recommended rate of 7 lbs. of nitrogen per 1,000 sq. ft. per year. Bermudagrass grown on the existing topsoil was acceptable using nitrogen below the lowest recommended nitrogen rate of 5 lbs. of nitrogen per 1,000 sq. ft. per year. Nitrogen source had little influence on turfgrass quality.

Based upon this research, superintendents will have evidence to support applying different rates of nitrogen based upon their soil type. BMPs would be amended to allow greater quantities of nitrogen to be applied to poor-quality soils, leading to higher quality turfgrass and better playing conditions, even when soils are not ideal.

Kaiyuan Tang and Travis Shaddox, Ph.D., University of Florida-Ft. Lauderdale. You may reach Travis Shaddox at shaddox@ufl.edu for more information.

Photo by: Travis Shaddox