Site-specific management of soil salinity in rice growing soils in the dry zone of Sri Lanka

Development of saline conditions in rice growing soils has become one of the major constraints that reduce the crop productivity in a number of irrigated areas in the Dry Zone of Sri Lanka. This study was conducted to assess the effectiveness of the application of sitespecific management practices to the salinity management classes identified based on the proximally sensed soil electrical conductivity on mitigation of soil salinity in rice growing soils in the dry zone of Sri Lanka. Two sites were selected in Galnewa and Thalawa areas in Mahaweli system ‘H’ where rice - OFCs cropping system has been practiced for nearly thirty years. The salinity management classes identified based on the proximally sensed electrical conductivity data of the topsoil in the Galnewa and Thalawa experimental sites in a previous study were used for the experiment. The resultant average electrical conductivity (EC_e) values were 0.38 dS m^-1, 0.48 dS m^-1 and 0.60 dS m^-1 in the identified salinity management class 1, 2 and 3 respectively. Non-salinity tolerant rice variety Bg 300 and salinity tolerant variety Bg 310 were investigated for their growth and yield performances without and with the application of Partially Burnt Rice Husk (PBRH). The EC_e levels in all the salinity management classes at the commencement of the Yala growing season were significantly higher than the EC_e levels recorded at the commencement of the Maha growing season indicating a greater salt stress for rice cultivation from the onset of the Yala season. The variety Bg 310 showed 25 - 45 % yield increment compared to the yield of the variety Bg 300 in the salinity management classes with comparatively higher electrical conductivity levels in the Yala growing season. The application of PBRH increased the rice yields and the benefits were more distinct under the salt affected conditions recording around 20% more yields from the higher rate of PBRH applied plots compared to the yields obtained from the PBRH unamended plots in the salinity management classes with higher electrical conductivity levels in the Yala growing season. Therefore, site specific varietal selection and application of PBRH to the salinity management classes identified based on the proximally sensed soil electrical conductivity has a considerable potential for further improvement of the rice yields in the dry zone of Sri Lanka. Further, the results of this work showed the need of further increasing of the PBRH rates in the salinity management classes with higher electrical conductivity levels.