Soil mineralization as effects of plant growth promoting bacteria isolated from microalgae in wastewater and rice straw application in a long-term paddy rice in Central Viet Nam

This study investigates the effects of rice straw and potential nitrogen fixing Bacillus subtilis (Bacillus sp.) isolated from seafood wastewater on carbohydrate- and nitrogen mineralization from a long-term rice paddy soil by four weeks anaerobic incubation. Soil collected at the depth of 0–15 cm from a long-term rice paddy cultivation, and set up as following: (1) Control (10 g air dry soil), (2) Rice straw (control ＋ 0.2% rice straw w/v), (3) Bacillus sp., and (4) Combine (rice straw 0.2% w/v and Bacillus sp.) was subjected to an incubator in dark at room temperature/ submerge condition for 4 weeks anaerobic incubation. As showed in results, content of decomposed carbohydrate ranged from 83–447 mg kg ⁻¹ soil. Content of extracted carbohydrate was not affected by rice straw application, but significant decreased with bacillus or rice straw-bacillus combine inoculation (2.0–2.2 times decreased) compared to Control treatment, which is closely to the initial soil extraction carbohydrate. In contrary, mineralization nitrogen increased 120% in Bacillus sp. inoculation compared to Control treatment, but Rice straw and Combine treatments resulted in immobilization more than nitrogen mineralization. Inoculation of Bacillus subtilis is recommended as a good environment friendly method to enhance the soil fertility and reduce nitrogen immobilization. Further research within rice plant is therefore needed to consolidate the preliminary results.