Effects of Fall Fertilization on Cold Resistance, Color, and Growth of Kentucky Bluegrass1

Fall fertilization of turf is usually avoided because it is thought to reduce cold resistance of plants composing the sward. Turf receiving N during this season exhibits color longer in fall and earlier in spring. The effects of periodic fall nitrogenous fertilization on the cold resistance, color, and growth of Kentucky bluegrass (Poa pratensis L.) were measured from September, 1970, to June, 1971, to ascertain if there is a period during the fall when N may be applied to produce color longer, yet not predispose plants to cold injury. Determinations of the cold resistance of crown tissue were made utilizing conductivity techniques for measurement of solutes diffused after cold treatment. Nitrogen at 2 kg N/200 m² (as NH₄NO₃) was applied to different plots on October 1 and 15, November 1 and 15, and December 1 and 15, 1970. An additional treatment received 1 kg N/200 m² on each date. The cold resistance of all treatments increased through the fall and early winter, peaked near the end of January, decreased slowly through February, and was lost rapidly in March and April. Early fall fertilization (through November 1) resulted in the greatest reduction in cold resistance in the fall, while late fall fertilization (after November l) resulted in the greatest reduction in the spring. Fertilization up until November 1 resulted in a color increase (i.e., chlorophyll increase) shortly after fertilization, and maintenance of color into early winter. Fertilization after November 1 did not produce substantial fall green-up. All treatments produced good spring green-up by mid-March; however, late fall fertilized plots (after November 1) had a higher chlorophyll content by mid-April. No treatment produced any measurable topgrowth from the end of November until May. Plots fertilized before November 1 produced additional yields in the fall, while plots fertilized later produced additional yields in the spring.