YIELD INCREASES OF TROPICAL GRASSES AFTER INOCULATION WITH SPIRILLUM LIPOFERUM

During the first year, 1974, inoculated Panicum maximum (guineagrass) and Digitaria decumbens (digitgrass) produced 80% and 61% more protein than uninoculated controls. In 1975, inoculation produced significantly higher protein and dry matter yields in Pennisetum americanum (pearl millet) and P. maximum. Projected yields using regression analysis of both pearl millet and guineagrass indicated that about 40 kg. N. ha-1 yr-1 were replaced by inoculation. Although overall production was lower during 1976, yield responses due to inoculation were similar to those of 1975 in guineagrass. Nitrogen fertilizer was required to enhance response to inoculation and higher rates of nitrogen fertilizer repressed response. Acetylene reduction verified that nitrogen fixation occurred, but did not correlate well with yield increases. Immunofluorescent techniques were used to specifically identify and monitor Spirillum lipoferum populations in the soil. These data are being used to evaluate inoculation procedures. Inoculation with Spirillum lipoferum has given yield increases for three consecutive years in Florida. This indicates: (1) Response to inoculation can be repeated; (2) economically important amounts of nitrogen can be replaced by inoculation; and (3) a high potential exists for developing grass-bacteria systems.