Organic Fertilizer Effects On Turf Quality, Turf Color and Digital Green Color Index (DGCI) Under Summer Heat Stress.

Abstract  Organic fertilizers are much less nutrient dense than the synthetic fertilizer commonly used on turfgrass, particularly with regards to nitrogen. This creates an obstacle to use of organic fertilizers as application of the large volumes of material required is labor intensive and may require turf managers to rent specialized equipment. This study was designed to determine whether a single application of organic fertilizer early in the growing season could be substituted for the monthly applications used with standard synthetic fertilizers, with the reasoning that renting equipment only once per season would be most cost-effective.  Single applications of organic products were made at 3 rates (48, 146, and 292 kg N ha^-1 yr^-1). Products included Milorganite, Sustane, Griggs Brothers and Squid Hydrolysate. Controls included a no-fertilizer treatment, ammonium nitrate (fast release, 100% soluble N)applied at 48 kg N ha^-1 yr^-1 , and ProTurf (slow-release N) applied at 48 and146 kg N ha^-1 yr^-1.  We quantified weekly turfgrass quality, color and DCGI from mixed Kentucky bluegrass (Poa pratensis L.)/ perennial ryegrass (Lolium perenne L.) turf from 6 July 2010 to 9 November 2010. Visual ratings of turf quality were measured using a 1-9 scale with 1 representing dead unresponsive turf and 9 representing dense weed-free turf. Visual ratings of turf color were performed using a 1-9 scale with 1 representing yellow/brown turf and 9 representing dark green turf. Digital Green Color Index was measured on a 0-1 scale with 1 indicating 100% green saturation. As expected, ammonium nitrate gave excellent quality and color on the first rating date. However, the high rate of Milorganite, Sustane, and Griggs Brothers gave similar quality and color. Both quality and color of the ammonium nitrate plots declined rapidly, while the plots fertilized with the organic products at the high rate maintained excellent color and quality throughout the study. In addition, the Milorganite and Griggs Brothers products at the medium rate resulted in quality and color comparable to the synthetic ProTurf at the same rate. Turf quality and color did not begin to decline until September in plots fertilized at the medium rate. Our results indicate that organic and synthetic slow release fertilizers can be safely applied at rates significantly exceeding 48 kg N in a single application, and that these heavy applications will continue to provide nutrients for 2-4 months after application. Thus turf managers who wish to use organic fertilizers could minimize application costs by applying more product in fewer applications.