Substitution of sodium for part of the potassium in mixed fertilizers

The two crops gave strikingly different responses to the various potassium and sodium levels. The crop yields indicated NaCl may be substituted for a portion of the potash in mixed fertilizers where the supply of potash is inadequate for the maximum growth of either crop; but, where an adequate amount of potash can be supplied, the substitution of sodium for part of the potash will not give as large yields of soybeans. For beets, at all potash levels the substitution of NaCl for fourth of the K2O resulted in no reduction in yield and in most cases significantly increased the yield, proving that for this crop the partial substitution of sodium for potassium would be a profitable practice. A relatively low level of potash and high level of sodium (75 pounds of K2O and 500 pounds of NaCl) gave the best results with beets. For beets, which require sodium per se, NaCl should be considered more as an important ingredient of the fertilizer mixture rather than as a substitute for part of the potash. With soybeans the substitution of sodium for one-fourth of K2O did not reduce the yield at the two lower levels (50 and 100 pounds of K2O) and these levels were below the needs of the crop. At the third level (150 pounds of K2O), which gave the largest yield of soybeans, the substitution of NaCl for one-fourth of the K2O significantly reduced the yield. For soybeans a relatively high level of potash (150 pounds of K2O) with no sodium gave the best results. Hartwell and Damon stated prophetically 27 years ago, "The gains in yield due to sodium assume unusual economic interest. In the future, conditions may be such that attention should be given to the use of our liberal supply of sodium salts as economic support to the limited amount of potassium." That statement might well be applied in 1947 to certain specific crops, such as beets, if the supply of potash is not ample to meet all requirements.