MSc

Pokkali is the unique system of rice cultivation in the water-logged coastal saline acid soils of Kerala. These are tidal wetlands characterized by multi stressed conditions such as acidity, salinity and waterlogging. Pokkali soils are the major salt affected soils in Kerala. Plant growth is affected by salinity at all stages of development resulting in reduced grain yield, dry matter production and total decrease in productivity. Excess sodium present in the saline environment creates adverse conditions for plant growth. High salinity in the root zone results in osmotic imbalance and ionic toxicity and thereby modifies nutritional status in soil and plant. In this context, the present study entitled “Management of soil salinity with calcium salts in rice–prawn farming system in Pokkali lands”, was conducted with the following objectives (i) to manage the soil salinity by application of calcium salts in pokkali lands (ii) to assess the effect of calcium salts on the growth and nutrition of rice, yield of prawn and soil properties. The experiment was conducted in the Thathapilli padasekharam (10º12’N, 76º26’ E) of Kottuvally Panchayath in Ernakulam district, during June 2017 to April 2018. The experiment was laid out in randomized block design with six treatments and four replications having plot size of 100 m². The treatments consisted of absolute control, calcium nitrate, calcium chloride, calcium sulphate, rock phosphate and dolomite at the rate of 45, 30, 34, 27 and 25 kg per plot so as to adjust the ratio of 1:5 for Na : Ca in the exchange complex on the basis of content of Na and Ca in soils. The Ca salts were applied before the rice crop only. Rice variety, Vyttila 6 was raised in the first crop season. Soil samples were collected from the treatment plots during three stages; before the sowing of crop, after the harvest of rice and after the harvest of prawn and analyzed for various physical (soil texture, bulk density), chemical (pH, EC, organic carbon, available N, P, K, Ca, Mg, S, Fe, Cu, Mn, Zn, B and exchangeable Na and Al) and biological parameters (microbial biomass carbon). Plant samples were collected at the time of harvest and analyzed for N, P, K, Ca, Mg and Na separately for shoot and root so as to assess the source sink relationship. Initial soil analysis revealed that texture of soil was sandy loam with a bulk density of 1.25 Mg m־³. Initial soil pH was 6.74 and electrical conductivity was 1.51 dSm¹־. Soil was deficient in available N, Ca, Mg and Cu and all other nutrients were in sufficiency level. Data on analysis of soil samples after the harvest of rice revealed that, all the treatments showed a superiority over control with respect to chemical parameters and biological parameter. The EC values ranged from 1.59 dSm־¹ to 1.75 dSm־¹. Exchangeable Na and Al content were highest in control. Among the different treatments, calcium nitrate registered peak values of organic carbon and available nutrients especially nitrogen and it reduced the available Fe content to an extent. Application of calcium nitrate significantly increased the grain yield (3300 kg ha־¹) and dry matter content and plant nutrient uptake. Increased shoot and root N content was also recorded and increment was reflected in the case of other plant nutrients also. Consequent reduction in the shoot Na content was observed as a result of reduced salinity. Highest Ca:Mg and K:Na ratio observed in plant samples of calcium nitrate treatment revealed better plant survival rate under salt stress. Next to calcium nitrate treatment, calcium chloride and dolomite treatments recorded higher in grain yield of 2192 kg ha־¹ and 2098 kg ha־¹ respectively and also the nutrient uptake. Soil analysis after the harvest of prawn recorded an increase in available major and secondary nutrients and reduced the Fe and Mn content in all the treatment with slight variation from control. Yield of prawn was highest in calcium treated plots as a whole than control plot and these variations in the productivity was a result of calcium salt treatments during rice cultivation and its residual effect retained in soil. Thus it can be concluded that application of calcium salts in pokkali soils increased the yield of rice and prawns, improved the soil properties and nutrient uptake by plants. Increase in grain yield was higher in calcium nitrate followed by calcium chloride and dolomite treatments. The highest B:C ratio was recorded in dolomite treatment because of the less input cost.