The effect of different levels of saline irrigation water and some amendments on microbial respiration, and acid and alkaline phosphatase activities in the rhizosphere soil during vegetative growth of Soybean

The applications of organic and inorganic amendments in saline soils may alleviate salinity effects on soil microbial activity and biochemical characteristics. In order to investigate the effects of different levels of saline irrigation waters, and organic and inorganic amendments on soil respiration, and acid and alkaline phosphatase activities in the rhizosphere soil during vegetative growth of soybean a factorial experiment consisting of five salinity levels (i.e. S1= 0.8 S2= 1.6 S3= 3.2 S4= 4.8 and S5= 6.4 dS/m from the sea water source) and five amendment treatments including T1 (control without amendments), T2 (20 ton gypsum ha-1), T3 (20 ton manure ha-1),T4 (10 ton gypsum +10 ton manure ha-1), T5 (15 ton gypsum +15 ton manure ha-1) arranged as randomized blocks design with three replications was conducted using pots under greenhouse conditions. The results showed that with increasing salinity level, soil respiration and enzyme activities of acid and alkaline phosphatases decreased significantly, however, the reductions were not similar and comparable among amendment treatments. Soil respiration and enzyme activities in treatments receiving higher amount of the combined organic and inorganic amendments were greater than other amendment treatments. Increasing the salinity levels in treatment without amendments application caused the reduction of soil enzymes activities and respiration. Whereas, application of manure and gypsum together, as organic and inorganic amendment increased the soil enzymes activities and respiration. Results indicated that the maximum soil respiration occurred in T5 treatments and the greatest soil enzyme activities occurred in T3 treatments relative to the other treatments.