The use of organic mulch and lime pelleting in field testing of Rhizobium strains under tropical conditions

Abstract

Two field experiments were conducted in the State of São Paulo, Brazil, to study the effect of soil and inoculation treatments on the nodulation and yields of the four legume species Glycine javanica, Teramnus uncinatus, Medicago sativa and Phaseolus vulgaris. Four Rhizobium strains were compared on each species. Three inoculation treatments were used, nil, peat applied with 10% sucrose, and peat applied with 45% gum arabic followed by lime pelleting. All treatments were replicated on mulched and unmulched soil. Mulching consisted of incorporating sugar cane bagasse into the soil surface. The technique of using mulch to tie up soil nitrogen proved to be an effective way of demonstrating differences in nitrogen fixing effectiveness of the Rhizobium strains in the field. It was also an efficient method of weed control. The technique of lime pelleting was shown to be of great use in promoting nodulation on the specialized species Medicago sativa and Phaseolus vulgaris. However, it had no effect on Teramnus uncinatus and only a very slight effect on Glycine javanica. The many differences in response of the various legume-Rhizobium combinations to mulch and inoculation treatment emphasizes the danger of drawing broad conclusions from experiments using only one combination. The potentials of mulching and pelleting are discussed with particular reference to the symbiotic specificity of the legume species under test.