Spatial variability of the Illinois soil nitrogen test: Implications for sampling in a turfgrass system

Nitrogen fertilization of turfgrass continues to be scrutinized due to environmental concerns. Practices that reduce fertilizer inputs without sacrificing turfgrass quality are needed, but a reliable test of N status in turfgrass is not currently available. The Illinois soil N test has been developed to predict crop response to applied N by measuring the amount of amino sugar N in the soil. Amino sugar N does not fluctuate as rapidly as other forms of N in soil. Our objective is to determine the spatial variation of amino sugar N in soil to determine sampling frequency requirements for use of the Illinois soil N test as a management tool on golf course fairways. Soil samples from 0 to 15, 15 to 30, and 30 to 45 cm were collected from golf course fairways in Minnesota and analyzed for amino sugar N concentration. Our data indicate that amino sugar N concentration decreases with depth but is not correlated to the concentration in the 0 to 15 cm layer. Amino sugar N concentrations measured on the four sampled fairways varied, but the spatial correlation present would allow for traditional soil sampling techniques to be used to assess the soil amino sugar N concentration within an area such as a golf course fairway.