Potatoes (Solanum tuberosum L.) were grown on a soil with a pH of 4.5 and containing 12 ppm of exchangeable manganese, and in sand cultures where the manganese concentration ranged from 0.2 to 10 ppm. Potassium was supplied in the forms of chloride, sulfate, carbonate, nitrate and hydroxide. On un-limed soils, the yields of tubers were in the following order: K2CO3 > KOH > KNO3 > K2SO4 > KCl. With lime, they were as follows: K2SO4 > KCl > KNO3 > K2CO3 > KOH. The potassium content of potato foliage tended to be lower when lime was added. Liming also reduced the chlorine content of plants by about 20%. Part of the reduction in the potassium and chlorine contents of plants could be the result of greater growth. KCl and K2SO4 increased the uptake of manganese and K2CO3 decreased it. Potassium uptake from the soil where that element was in short supply was in the following order: K2SO4 > KCl > KOH > K2CO3 > KNO3. In sand cultures where K was plentiful, potassium sources had no effect on potassium uptake by plants. Manganese toxicity builds up very gradually in potatoes. In a period of 9 to 10 weeks, the manganese content of the lower leaves reached a level of 400 ppm (stage where the first symptoms appear), but 5 weeks later they contained 1,200 ppm. Plants containing an excess of chlorine were lighter in color and contained less nitrogen in their leaves but more in their stems.
Effect of Potassium Sources on Growth and Potassium Uptake of Spinach
