The Yields and Composition of Five Grasses Growing in the Humid Mountains of Puerto Rico, as Affected by Nitrogen Fertilization, Season, and Harvest Procedures

Abstract

The productivity of Napier, Guinea, Para, Pangola, and molasses grasses, as affected by nitrogen fertilization and season of the year under both cutting and simulated grazing management, were determined under conditions typical of the humid mountain region of Puerto Rico. Molasses grass yielded much less than the others, all of which were very similar in yield, response to nitrogen fertilization, and seasonal growth rates with both harvest procedures, except that Guinea grass outyielded the others with grazing management. With cutting management and 400 pounds of nitrogen per acre yearly, Napier, Guinea, Para, and Pangola grasses yielded about 24,000 pounds of dry matter per acre yearly having about 8 percent of protein. Yields were lower with grazing than with cutting management. Season of the year markedly affected growth of all grasses with lowest yields occurring from December through March. Seasonal variations were accentuated by nitrogen fertilization. Annual yields of the Para, Guinea, Napier, and Pangola grasses increased rapidly with nitrogen rates up to 400 pounds. However, response was generally limited to the 200-pound rate during seasons of slow growth, but was strong up to at least the 400-pound rate at other times. Molasses grass responded only to the application of 200 pounds of nitrogen per acre yearly at all seasons. Protein content of all the grasses was similar, increased with nitrogen rates, was higher during seasons of slow growth, and lower with cutting than with simulated grazing management. Napier grass had the lowest drymatter content, while Guinea grass had a markedly higher calcium and magnesium content than the others. Otherwise, the forages were very similar in mineral and lignin content. There was little difference in efficiency of nitrogen utilization by the highest yielding grasses. Efficiency was lower with grazing management, higher during seasons of fast growth, and decreased with increasing nitrogen rates