In India where there is a wide heterogeneity in soils, the use efficiency of added fertilizer nutrients is very low. This limits crop productivity, results in loss of costly inputs and adds to environmental pollution. Hence utmost priority should be given to enhance the use efficiency of these costly fertilizers. In an effort to find out a cheap, indigenous and effective alternative to the imported K fertilizer, muriate of potash, a series of investigations were carried out in the Kerala Agricultural University from 1993 to 2004 with several low cost materials in which Na of common salt emerged as a partial substitute for K of muriate of potash. In these experiments, it was observed that addition of common salt resulted in changes in tissue concentrations of major and secondary nutrients with resultant changes in yield. The present paper discusses the interactive effect of applied K and Na on the nutrient concentration, uptake efficiency,agronomic efficiency and yield of some common tropical crops. Separate field experiments for each crop were conducted in statistically laid out plots. The treatments in all these experiments were combinations of K and Na at different levels of substitution or addition. The recommended dose of K as per the package of practices recommendations of the Kerala Agricultural University for the respective crop was taken as the control in each experiment. The soil of the experimental area belonged to the family of Loamy skeletal Kaolinitic Isohyperthermic Rhodic Haplustult with an acidic reaction and low status of K. The area enjoyed a humid tropical climate with a mean annual rainfall of 2000mm.The crops tested were cassava, banana, coleus, green and red amaranthus, cow pea and tomato. Plant weight and yield were recorded in each experiment. Nutrient concentration in plants were determined following standard analytical procedures and uptake calculated.Agronomic efficiency and recovery efficiency were worked out. The results revealed significant changes in nutrient concentration and uptake in all the crops tested. A combination of K and Na at 50:50 proportions(substitution of half K with half Na ) was found to be the most beneficial treatment in terms of agronomic and recovery efficiency of added nutrients.The plants in this treatment recorded higher concentrations of all the major and secondary nutrients in tissues in comparison with those receiving full dose of K.The increase in concentrations ranged from 3-19 percent for N, 1-11 percent for P, 7– 48 percent for K, 38-127 percent for Ca and 48-148 percent for Mg in the crops tested. In the case of plant uptake, up to 36 percent increase was obtained for N, 66 percent for P, 96 for K, 290 for Ca and 203 for Mg in the 50 K:50 Na treatment in comparison to the full K treatment resulting in a higher agronomic and recovery efficiency. K substitution at 50 percent was also found to be the most beneficial in terms of yield in cassava,rice,banana,coleus and tomato. In cow pea and green and red amaranthus, increase in yield was also recorded for higher doses of Na when supplied along with 50 percent K . The yield increase obtained in 50 K : 50 Na treatment in comparison with the 100 % (full recommended dose) K treatment ranged from 12 to 31 percent in various crops. The results thus point out that in acid soils when half dose of K is substituted with Na of common salt, the use efficiency of plant nutrients can be increased which results in higher dry matter accumulation and yield. Increased agronomic and recovery efficiency reduces the loss of added nutrients which lessens the risk of environmental pollution.Hence 50 percent substitution of K of muriate of potash by Na of common salt not only saves fertiliser cost , but also enhances income of farmer by an increase in yield, reduces nutrient loss and lessens environmental pollution .