Effect of Nitrogen Rates, Harvest Interval and Cutting Heights on Yield and Composition of Star Grass in Puerto Rico

Abstract

The effect of nitrogen rates, length of harvest intervals, and cutting heights on the yield and composition of a Puerto Rico cultivar of Star grass were determined during 2 consecutive years. Dry matter yields increased with nitrogen rates at the two cutting heights tested. However, the response at the various harvest intervals tested (30, 45, 60 and 90 days) was dependent on cutting height. Low cut Star grass responded sharply up to 400 to 600 pounds of nitrogen depending on harvest interval. High cut Star grass responded sharply to 400 to 600 pounds of nitrogen depending on harvest interval. The crude protein yield and content increased up to the highest nitrogen rate tested at all harvest intervals and cutting heights. The percent nitrogen recovered in the forage was of the same magnitude as that obtained with other grasses. However, the nitrogen rates did not have a pronounced effect on the percent nitrogen recovered in the forage. The proportion of leaves to stems was not affected by nitrogen rates. Leaves were higher in protein content than the stems at all nitrogen rates and harvest intervals. Dry matter yields increased but protein content decreased as length of harvest interval increased from 30 to 90 days. Length of harvest interval did not affect the percent nitrogen recovered in the forage, but had a marked effect on chemical composition of the forage. The content of N, P and K decreased at both cutting heights and at all nitrogen rates as the length of the harvest interval increased from 30 to 90 days. The apparent digestibility of the forage decreased and lignin content increased as length of harvest interval increased. Star grass produced higher yields when cut low than high. The difference was more evident as the length of the harvest interval increased from 30 to 90 days.