Effect of fertility ratios on growth and turf quality of perennial ryegrass (Lolium prenne L.) in winter

Perennial ryegrass (Lolium prenne L.) has been introduced to Japan as a cool season turfgrass. In spite of relatively mild winter in most parts of the country, it still goes to winter dormancy. A well‐balanced fertility ratio and rate may prevent such dormancy without causing winter injury. Therefore, this experiment was designed to find a balanced rate and ratio among nitrogen (N), potassium (K), and phosphorus (P) fertilizers in order to prevent winter dormancy and promote growth during the winter in Japan. Yorktown 2 perennial ryegrass was used in this experiment. Nitrogen and K application rates were 50, 150, 250, 350, 450, 550, and 650 kg K/ha; whereas P rates were 50, 150, and 250 kg P/ha. These rates were applied in 30 different ratios. Growth, color, and density of the turf were estimated and used as the parameters for finding a suitable rate and ratio for these three major nutrients. Color, density, and growth were increased as the rate of N fertilizer increased, but there was no visual response to P or K rates. It is suggested that increases in color, density, and growth were function of N rates, whereas K and P rates maintained the cold hardiness of the turf when high N rates were applied under the conditions of this experiment. Fertility ratio and the rates of 450 kg N/ha, 250 kg K/ha, and 50 kg P/ha were sufficient to prevent dormancy, promote growth, and produce good quality turf throughout the winter. Thus, it is concluded that fertility ratios and rates are the main factors limiting growth and quality of perennial ryegrass in transitional zones similar to Japan.