Effects of Nitrogen Fertilization and Frequency of Cutting on the Yield and Composition of Guinea Grass in Puerto Rico

Abstract

The effects of nitrogen rates ranging from 0 to 1,600 pounds of N per acre yearly and of 40-, 60-, and 90-day harvest intervals on the yield and composition of Guinea grass and on soil acidity were determined for 2 consecutive years. Yields increased with nitrogen fertilization up to the 800-pound level, while protein content and protein yields increased up to the 1,600-pound level. About half of the fertilizer nitrogen was recovered in the forage when 800 pounds or less were applied per acre yearly. Efficiency of utilization, in terms of dry matter produced per pound of nitrogen, decreased with increasing rates. The phosphorus content of the forage decreased while the lignin content increased with nitrogen rates. Fertilization with nitrogen had no apparent effect on the calcium, potassium, or magnesium content of the forage. Yields and lignin content of the forage increased while the protein. phosphorus, calcium, magnesium, and potassium contents decreased with length of harvest interval. A 60-day harvest interval and 400 to 800 pounds of nitrogen per acre yearly, depending on rainfall, seemed to be the optimum combination. With the higher nitrogen rate, Guinea grass yielded 32,733 pounds of dry matter (about 73 tons of green forage) per acre yearly with 9.6 percent of protein. With this treatment Guinea grass removed about 70 pounds of phosphorus, 286 pounds of calcium, 169 pounds of magnesium, 500 pounds of nitrogen, and 330 pounds of potassium per acre yearly. About the same yields were produced during each of the two years although rainfall varied greatly. Seasonal yields varied widely. The application of 800 pounds of nitrogen as ammonium sulfate per acre annually over a 2-year period caused a drop of 2.1 pH units and a loss of 5.5 m.e. of exchangeable bases per 100 gm. in the upper 6 inches of soil.