Volume 37, 11-19

Tropical Grasslands (2003) Volume 37, 11–19

Nitrogen fixation and growth of cowpea (Vigna unguiculata) and yam bean (Pachyrhizus erosus) in a sodic soil as affected by gypsum and sulphur inoculated with Thiobacillus and rhizobial inoculation

N.P. STAMFORD, A.D.S. FREITAS, D.S. FERRAZ, A. MONTENEGRO and C.E.R.S. SANTOS

UFRPE — Department of Agronomy, Recife, Brazil

Abstract

A greenhouse experiment was carried out to evaluate the effects of applying gypsum and sulphur inoculated with Thiobacillus, on nitrogen fixation and growth of cowpea and yam bean, inoculated with specific rhizobial strains. A Neosol Fluvic Salic sodic soil from the Brazilian semi-arid region was submitted to treatments consisting of sulphur inoculated with Thiobacillus (0.6, 1.2 and 1.8 t/ha) and gypsum (1.8 and 3.6 t/ha). A control treatment had no sulphur or gypsum applied. Cowpea and yam bean were inoculated with Bradyrhizobium strains NFB 700 and NFB 450, respectively, selected for saline conditions. Treatments without rhizobia were included as controls. Sulphur with Thiobacillus was more efficient than gypsum, in reducing soil pH, electrical conductivity (EC) and exchangeable sodium. Sulphur with Thiobacillus reduced pH (8.2 to 4.7) and E C of the soil saturation extract (15.3 to 1.7 dS/m) to values below those adopted in saline and sodic soil classifications. Nodulation, dry matter production and nitrogen and sodium uptake were affected by the ameliorants. Rhizobial inoculation with specific strains was very effective and, when applied with soil ameliorants, increased nodulation, total nitrogen and shoot dry matter yield in both legumes.