Regulation of plant na/k ratio for productivity enhancement in pokkali rice
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Date
2019
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Department of Agronomy, College of Horticulture, Vellanikkara
Abstract
Pokkali is a sustainable and unique rice farming system in coastal saline soils of Kerala. Salinity, submergence and high inherent acidity are the major issues underlying this special system of rice cultivation. In saline soils, higher Na content and the resultant high ratio between Na and other cations like K, Ca and Mg within the plant becomes detrimental for crop. Maintaining a low ratio of Na with other cations especially with K, is considered to be an yield determining and salt tolerance criterion in crops. Ameliorants containing sufficient amount of calcium inhibits the effect of soil acidity as well as soil salinity. As no response to soil application of nutrients is observed in Pokkali rice, foliar nutrition of K is expected to maintain nutritional balance within the plant. Hence the study was conducted with the objective to study the effect of the narrowing down of Na/K ratio in Pokkali rice by liming and foliar application of K.
The study entitled “Regulation of plant Na/K ratio for productivity enhancement in Pokkali rice” was conducted at Rice Research Station, Vyttila. VTL8 was the variety used for the field experiment. Treatments included soil application of different levels of lime (500, 1000 kg ha-1) or dolomite (800, 1600 kg ha-1) alone and these treatments followed by foliar spray of sulphate of potash (2% SOP at 20 and 40 DAT). These treatments were compared with foliar spray of SOP alone and a control (no amelioration, no foliar spray). Various biometric observations, soil chemical characteristics and plant nutrient content were assessed during and after the field experiment. Crop duration was 137 days.
Both growth and yield parameters exhibited significant variation among treatments. Number of tillers per sq. m, number of panicles per sq. m, percentage of filled grains and grain yield (2975 kg ha-1) were found to be higher for soil application of lime along with foliar spray of SOP at 20 and 40 DAT. Effect of dolomite @1600 kg ha-1 on yield was higher than the effect of lime @ 500 or 1000 kg
ha-1. Foliar spray of K resulted in comparable yield to that of lime @ 1000 kg ha-1. Amelioration with dolomite @1600 kg ha-1 with or without foliar spray could significantly enhance the dry matter production and leaf area index and could result in a yield next to the best treatment.
Liming influenced the plant nutrient content in Pokkali rice at various stages. Higher potassium, phosphorus and magnesium content were observed when applied with lime @1000 kg ha-1+ K (2% spray) at 20 and 40 DAT. Higher calcium content was observed in plots treated with dolomite @ 1600 kg ha-1.
In acid saline soils, higher Na/K ratio is considered as the major yield limiting factor. Treatments significantly influenced the plant Na/K ratio at different stages of crop growth. Control treatment recorded highest Na/K ratio at all the stages. This indicated that amelioration and foliar spray of SOP had significant influence in reducing the plant Na/ K ratio. Correlation analysis also showed that grain yield had significant negative correlation with Na/K ratio at 90 days after transplanting. This indicates that Na/K ratio at flowering stage is most critical. Application of lime @1000 kg ha-1 or dolomite @ 1600 kg ha-1 along with SOP (2% spray) at 20 and 40 DAT could narrow down the Na/K ratio at flowering stage and thereby increase the yield significantly. A reduction in soil pH was observed in these treatments at flowering stage.
In addition to the correction of soil acidity, application of lime and dolomite could improve the availability of calcium and magnesium content in soil as well as enhance their uptake by the crop. Economic returns were also found to be higher on application of lime @1000 kg ha-1 and 2% foliar spray of SOP. Hence application of lime @1000kg ha-1 and 2% foliar spray of SOP at 20 and 40 DAT can be recommended to increase the yield of Pokkali rice.
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174815