Evaluation of Dry Matter Productivity of Thirteen Tropical Grasses Adapted to Iriomote Island, Yaeyama Region, Okinawa, Japan

Abstract

Thirteen tropical grasses were evaluated for seasonal and annual dry matter productivity. The field experiment was conducted for three years at Iriomote island, Okinawa, Japan (24°24'N, 123°48'E). The same management practices were applied for all genotypes in every season. Crop growth rate (CGR) of all genotypes increased in spring and summer season, and CGR of winter fell to 39% on the average in summer season. The CGR values of Brachiaria and Setaria genotypes were higher than other grasses from spring to autumn seasons. The CGR values of the leading three genotypes in the local cultivation (Chloris gayana Kunth cv. Katambora, Cynodon nelmfuensis Vanderyst, and Panicum maximum Jacq. cv. Gatton) were comparatively high in winter season. Annual mean CGR was highly correlated with CGR in spring and summer seasons. In the second year when there was little precipitation in summer the growth of two Chloris genotypes deteriorated markably. Chloris genotypes were most vulnerable to drought among the 13 grasses. Although C. gayana Kunth cv. Katambora has the largest cultivation area in Okinawa Prefecture, the productivity was relatively low among the 13 species. Principal component analysis was performed to evaluate dry matter productivity of all genotypes. The first two principal components explained about 85% of total variability. It is concluded that creeping signal grass (Brachiaria humidicola (Rendle) Schweich), signal grass (Brachiaria decumbens Stapf), purple pigeon grass (Setaria incrassata Hochst) and setaria (Setaria sphacelata var. sericea cv. Kazungula) were superior in growth of warm seasons for 3 years with high annual dry matter production to other genotypes.