Transitioning to Natural Organic Fertilizers.

Natural organic (NO) fertilizer use in turf management has increased in recent years. Research indicates that these products may release between 30 and 90 percent of the amount of nitrogen (N) released by synthetic fertilizers. Because of this incomplete N release, turf managers may see limited turf response if they apply NO products using the same N rates as they previously used. This study was designed to evaluate turfgrass response under three different management programs for transitioning to NO fertilizer use. Programs included applying two different NO fertilizers or a synthetic controlled-release fertilizer (PCSCU) at a standard (1X) rate (147 kg N ha^-1 yr^-1); increasing the rate to 1.5X (221 kg N ha^-1 yr^-1);  and alternating the NO fertilizers with the PCSCU, increasing the organic : synthetic ratio over a three-year period.  Visual color and quality ratings were collected monthly, as well as chlorophyll index measurements (FieldScout CM1000 meter). Clipping yield and N content were measured one month after each application of fertilizer. The 1.5X rate treatments generally resulted in the highest color, quality, and chlorophyll index measurements. During late fall and winter, PCSCU applications maintained better plant color, although 1.5X rate NO treatments were similar. The 1X NO treatments usually had lower color, quality, and chlorophyll index than all other treatments, including PCSCU alone. Incomplete N release from NO fertilizers should be compensated for by either increasing the rate of application or alternating NO and synthetic fertilizers during the first two or more years of NO fertilizer use.