Nodulation and nitrogen fixation in legume trees

Abstract

Although herbaceous legumes are much better known, the vast majority (97% of Caesalpinioideae, 95% of Mimosoideae and 38% of Papilionoideae) are tree species. In contrast to the well known herbaceous species which all are able to form nodules and fix N₂, of the tree species many do not nodulate. Only a minor part of these species (18%) has been examined in this respect. Recent studies of the more important Brazilian forest trees have added 63 nodulated species and 16 non-nodulated species to the lists given in the literature. Species which nodulate should be planted in inocuolated seed beds which proportion better establishment in the field and faster growth than N fertilized seed beds. For this, host plant specificities have to be letter known to permit Rhizobium strain selections for inoculant production. For some important tree species (Mimosa caesalpiniaefolia, Prosopis juliflora and Leucaena Ieucocephala) inoculants are already available. Estimates of N₂ fixation by tree species reach 600kg N/h/yr.