Synopsis Napiergrass, guineagrass, and paragrass responded strongly to annual applications of up to 800 pounds of nitrogen per acre. Protein content and protein yields increased up to the highest N level tested. Yields increased but quality of the forage decreased with length of harvest interval. Between 30,000 and 45,000 pounds of dry matter averaging about 9.5% protein were produced annually per acre.

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

The effects of phosphorus applications on yields and phosphorus content of otherwise well-fertilized tropical grasses growing on three typical soils of the Humid Region of Puerto Rico were determined. Napier grass responded strongly in yield to applications of 150 pounds of P2O5 per acre yearly on both Múcara and Catalina clay soils at Orocovis. The phosphorus content of the forage increased with applications of up to 300 pounds of P2O5 per acre yearly on both soils. On the other hand, Napier, Guinea, and Pangola grasses, growing on a Fajardo clay formerly in moderately fertilized sugarcane for many years, did not respond in yield or phosphorus content to applications of phosphorus over a 5-year period. Various methods of determining "available" soil phosphorus did not give satisfactory results with these soils.

The effects of applying 600 pounds of nitrogen per acre yearly from five sources on yield and composition of Napier grass growing on a latosol in the humid Mountain Region of Puerto Rico over a 3-year period were determined. Dry-matter yields and the calcium, phosphorus, manganese, and potassium content of the forage were unaffected by the nitrogen source. However, less protein was produced with urea and ammonium hydroxide than with ammonium sulfate, sodium nitrate, or ammonium nitrate, showing that the former are somewhat less efficient providers of nitrogen under the conditions of this experiment. Forage yields were lower but protein content was higher during the "winter" months of lower rainfall, shorter days, and cooler weather.

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