Effect of sulphur inoculated with Thiobacillus on soil salinity and growth of tropical tree legumes

A greenhouse experiment was carried out with the objective of evaluating the effects of the elementary sulphur inoculated with Thiobacillus, compared with gypsum, in the amendment of a alluvial sodic saline soil from the Brazilian semiarid region, irrigated with saline water and grown with the tropical legumes leucena and mimosa. The treatments consisted of levels of sulphur (0; 300 and 600 kg/ha) and gypsum (1200 and 2400 kg/ha), irrigation using different waters containing the salts NaHCO3, MgCl2, CaCl2, NaCl and KCl, with different electrical conductivities (ECs: 0.2, 6.1 and 8.2 dS/m at 25°C). Based on the results it appears that saline water increased exchangeable Na+, K+, Ca2+, Mg2+, and soil pH. Sulphur inoculated with Thiobacillus was more efficient than gypsum in the reduction of the exchangeable sodium of the soil and promoting leaching of salts, especially sodium. Sulphur inoculated with Thiobacillus reduced the EC of the soil saturation extract to levels below that adopted in soil classification of sodic or saline sodic. Leucena was more tolerant to salinity and mimosa more resistant to acidity promoted by sulphur inoculated with Thiobacillus.