Nitrogen fixation and transfer by some tropical and temperate pasture legumes in sand culture

Abstract

Nitrogen fixation by four tropical pasture legumes-Indigofera spicata Forsk., Desmodium uncinatum (Jacq.) D.C., Lotononis bainesii Bak., and Stylosanthes bojeri Vogel-and by lucerne (Medicago sativa L.) and white clover (Trifolium repens L.), was measured in sand culturere in the glasshouse. During a two year period lucerne and white clover fixed significantly more nitrogen than any of the tropical species. Indigofera spicata fixed as much nitrogen as lucerne during the first year, but was only half as productive as lucerne during the second year. Lotononis bainesii added as much nitrogen as Indigofera spicata, while smaller amounts were fixed by Desmodium uncinatum and Stylosanthes bojeri. It is likely that nitrogen fixation by Lotononis bainesii, Desmodium uncinatum, and Stylosanthes bojeri was restricted by strains of Rhizobium that were not fully effective. Paspalum commersonii Lam. was grown in association with four of the legumes. White clover was the most efficient nitrogen donor in the first year and Desmodium uncinatum was superior to the other legumes during the second year. The proportion of nitrogen transferred to the grass over two years was only 0.6 to 1.7 per cent of total fixation. Some possible reasons for this result are discussed.