Abstract1. The present paper gives a critical re‐examination of different data and conceptions on the action of sodium in relation to deficiency symptoms and yield response.2. The importance of sodium for different agricultural crops is discussed in relation to the replacement of potassium and independent sodium effects.3. The results of pot experiments on oats, reported in the literature, indicate that sodium has an independent function other than that of replacing potassium. Both the nitrate and chloride of sodium appeared to be suitable for oats.4. Field experiments testing sodium for early potatoes in Holland showed little effect on yield of tubers, but there were effects on the tops. Even at high levels of potassium there were responses in yields of main‐crop tubers from dressings of sodium. The effect of sodium was studied by comparing sodium nitrate with calcium nitrate. When sodium chloride was applied to potatoes, either as common salt or with 20‐40% muriate of potash, there were decreases in yield and starch contents of the tubers.5. Results are given of recent Dutch experiments with fodder beet, testing sodium as nitrate of soda. The influence of soil type and addition of farmyard manure is discussed.