Legume trees in semi-arid and arid areas

Abstract

A review of the research and development activities on nitrogen fixing trees for semi-arid regions is presented. In the period from 1980 through 1983 much new information on pod productivity, on natural stand nitrogen fixation and on greenhouse mineral nutrition has become available. Early results from small plot plantation work indicate a biomass productivity of 10-13 dry metric tons per hectare per year. Clones have been made of promising individual trees and research on rooting of cuttings is rapidly approaching commercialization. Tissue culture propagation of semi-arid nitrogen fixing trees has only just begun. Procedures have been developed employing subsoiling and herbicides that yield more than 90% survival on sites receiving 500 mm annual rainfall. A tabular review is presented of the major research organizations and donors involved in semi-arid nitrogen fixing trees. Major technical constraints are coping with semi-arid soils that are generally low in available phosphorus, iron, zinc and manganese, range in soil texture from cracking clays to high bulk density sands or rocky desert pavement, and that vary in pH from 6.5 to 9.5. Pest management issues (insects and diseases) have not yet been studied in semi-arid nitrogen fixing trees and should be addressed before large scale plantations are undertaken. The excellent progress made from 1980 through 1983 suggests a very bright future for semi-arid nitrogen fixing trees.