Plant-available soil nitrogen fluxes and turfgrass quality of Kentucky bluegrass fertilized with humic substances

High quality turfgrass requires adequate amounts of nitrogen (N) fertilizer. However, excess N application can increase N losses via leaching and gaseous emissions. Enhanced efficiency fertilizers (EEF) and humic substances have been used to decrease N losses to the environment. A two-year field experiment was conducted on a native soil with Kentucky bluegrass (Poa pratensis L.) to investigate if the addition of humic substances to fertilizers could be classified as an enhanced efficiency fertilizer. To determine this, the objectives were: a) to determine if incorporating humic substances will increase the plant-available N collected on ion exchange membranes (IEM) over a growing season and b) to determine the N release (NR) curves of the fertilizer treatments using the mesh bag technique. Fertilizer treatments included humic-coated urea (HCU), poly-coated humic-coated urea (PCHCU), urea + humic dispersing granules (HDG), poly-coated sulfur-coated urea (PCSCU), stabilized N, urea, and a nontreated control. Overall, the addition of humic substance to fertilizers did not improve turfgrass quality compared with fertilizers alone. Additionally, all fertilizer treatments had improved turfgrass quality relative to the nontreated control and provided acceptable turfgrass quality for almost all of the growing season. Over the growing season, PCHCU had 25% greater inorganic N captured on IEM compared with all other treatments. Both PCHCU and PCSCU show extended NR curves with PCHCU having a greater release period. In conclusion, PCHCU increased plant-available N concentrations, released it slowly, and should be classified as an EEF.