Temporal Variation of Amino Sugar Nitrogen in Turfgrass Soils.

Nitrogen (N) fertilization of turfgrass continues to be scrutinized due to environmental concerns.  Practices that reduce fertilizer inputs without sacrificing turfgrass quality are needed.  However, 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 agricultural soils.  The objectives of this study were to determine the temporal variation of soil amino nitrogen in managed turfgrass systems and the contribution of thatch to amino sugar N levels.  Studies were established in 2004 and 2008 to examine both the contribution of thatch and seasonal fluctuation of amino N in a Kentucky bluegrass soil profile.  Replicate soil cores were tested weekly for 52 weeks during each study.  There was no net change in the amino N concentration of the soil during the study period.  No significant differences (P=0.05) in amino N concentration were detected due to fertilizer application on any of the weekly sampling dates either in 2004.  Thatch accounted for 9% of the total amino N in the top 15 cm of soil.  Our results indicate that the Illinois Soil N Test may have value for identifying sites that will be either unresponsive to added fertilizer nitrogen, or, at increased risk for nitrate leaching due to added fertilizer N.