SUMMER COLOR AND FALL COLOR RETENTION OF KENTUCKY BLUEGRASS RECEIVING VARYING AMOUNTS AND TIMING OF INORGANIC OR INORGANIC-ORGANIC COMBINATIONS OF NITROGEN
Varying levels of N as ammonium nitrate, ammonium nitrate phosphate, ammonium phosphate sulfate, and monoammonium phosphate (0.83–2.51 kg N/100 m2/season) applied in three replications at 6-wk intervals (mid-May to mid-August) did not markedly affect the summer color quality of Kentucky bluegrass turf when the season was warm. When the season had a below-normal number of accumulated degree days, however, there was a positive correlation and linear regression between green color of the turf and the amount of N applied. When organic N (processed sewage) was used in two of the applications and inorganic N in one of the three replications, the green color response of the turf during summer was even more influenced by growing conditions. With a below-normal accumulation of degree growing days in 1975 there was no difference in green color from varying levels of organic N while in 1976 with an above-normal accumulation of degree days there was a better green color development with the higher levels of organic N. In the fall, higher levels of green color were maintained from higher levels of inorganic N. Varying the amount of nitrogen within the three application dates did not affect this correlation. When two applications of organic N were used in combination with one application of inorganic N, however, this correlation between better green color and higher rate of N did not show up until very late when all scores were relatively low. Although the range of scores for inorganic and inorganic-organic combinations had a similar range on any particular date in the fall, the application of inorganic N on the final date gave the best color retention and those receiving organic N on the final date tended to go dormant earlier. Where early spring green color or fall color retention of the turf is desired in northern climates, the inorganic form of N is more suitable than the organic form. The amount of color was positively correlated with the amount of inorganic N applied during the summer fertilizer program.