SOIL SALINITY AND RICE PRODUCTIVITY MANAGEMENT WITH SPECIAL REFERENCE TO CYANOBACTERIA

Abstract

Laboratory and field experiments have been conducted during 2000-2001 to assess the role of Cyanobacteria for maintaining rice productivity, improving soil fertility and reclaiming soil salinity. Saline soils from two saline areas viz. Fultala village of Batiaghata upazila under Khulna district and Mahmudpur village of Shaymnagar paz under Satkhira district were selected for the study. The experiments were conducted in two phases. Firstly, soil samples were collected from two sites and microbiological study was done for isolation and identification of Cyanobacteria, and measuring their N-fixing capacity. Fifteen taxa of Cyanobacteria taking seven from Fultala and eight from Mahmudpur sites were isolated, identified and brought under pure unialgal cultures. Out of 15, six isolates of Cyanobacteria three from Fultala viz. Sccytonema, Oscillatoria, Fischerella, and three from Mahmudpur viz. Anabaena, Scytonema and: Westiellopsis were found promising in respect to fast growth and N fixation capacity at high salinity. BGA inoculum was prepared through composite cultures of these six isolates for field experiments. Secondly, two identical field trials were conducted at both sites to observe the effect of Cyanobacteria on the productivity of rice, soil fertility and soil salinity for two consecutive years (2000 and 2001). The six treatment combinations used for the experiment were — Control, Recommended Fertilizer Dose (RFD) i.e. NgoP22K33Ss, NgoP22K33Ss — 20%N, NgoP22K33Ss — 20%N+ Cyanobacteria, NgoP22K33Ss — 40%N and NgoP22K33Ss — 40% N + Cyanobacteria. The experiment was laid out in randomized complete block design with three replicaiions. The modern rice varieties BRRI dhan28 and BRRI dhan31 were used as test crops during boro and T.aman seasons, respectively. Results of the present investigation demonstrated that RFD — 20%N+ Cyanobacteria treatment significantly enhanced rice yield and productivity in saline soils, and maintained the highest yield and productivity throughout the experimentation. Application of Cyanobacteria inoculum in saline soils resulted slightly increased in organic matter, total nitrogen, available phosphorus, available sulphur and exchangeable potassium contents in soils while resulting in a decrease in pH and electrical conductivity (EC). Results of the present investigation indicated that Cyanobacteria inoculum might be used for maintaining rice productivity, improving soil fertility and reclaiming soil salinity.