Effect of dual inoculation with arbuscular mycorrhizal fungi and sulphur-oxidising bacteria on onion (Allium cepa L.) and maize (Zea mays L.) grown in sandy soil under green house conditions

Thirty isolates of Thiobacillus sp. were successfully isolated on Thiobacillus enrichment medium from different plants rhizosphere. Thiobacillus A1, Thiobacillus A2 gave the lowest pH and the highest total sulphate in liquid medium after one week. These two isolates were used as bioinoculants. The effect of inoculation with the two selected isolates and/or arbuscular mycorrhizal fungi (AMF) on onion and maize plants was studied in pot experiment under green house conditions. Mineral fertilizers were applied at the recommended dose of N, P, K and sulphur(S) besides rock phosphate (RP) as P fertilizer. Results showed that, inoculation gave significant increases in N, P, K and S concentrations in plants rhizosphere soil at the sampling periods of 60 and 90 days from planting. Highest values of nutrient concentrations were found in soils fertilised with NK + S + rock phosphate (RP) and inoculated with AMF + Thiobacillus A1. Total sulphur-oxidising bacterial counts, dehydrogenase activity (μg TPF/100 g dry soil Day−1) and CO2 evolution (mg CO2/100 g soil) were determined in rhizosphere of the tested plants. Soil biology was affected by either mineral or biofertilizer treatments. Significant differences were found for samples collected after 60 days for onion and 90 days for maize fertilised with NK + S + RP and inoculated with AMF + Thiobacillus A1 which gave the highest significant differences over control. Mycorrhizal spores number and AMF infection percentages in plants roots greatly affected by AMF inoculation especially when combined with Thiobacillus A1 after 60 days from planting. Dry weight of onion bulbs and maize shoots as well as NPK contents significantly affected by AMF and Thiobacillus inoculations than the control plants.