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figure 4.7 Potassium concentration in aboveground barley throughout the growing season of treatments with and without N supply (a) in the dry matter, (b) in the tissue water, and (c) in the tissue water with or without fertilizer K. (Adapted from A.E. Johnston and K.W. Goulding, in Development of K Fertilizer Recommendations. Bern: International Potash Institute, 1990, pp. 177-201.)

suboptimum and optimum supply. Such an example is shown in Table 4.5 (65). Maximum fruit yield was obtained in the K2 treatment at K+ concentrations in the range of 25 to 35 mg K/g dry matter (DM). In the K+ concentration range of 33 to 42mg K/g DM, the optimum was surpassed.

The optimum K+ concentration range for just fully developed leaves of 25 to 35 mg K/g DM, as noted for tomatoes, is also noted for fully developed leaves of other crop species, as shown in Table 4.6 (52). For cereals at the tillering stage, the optimum range is 35 to 45 mg K/g DM. From Table 4.5, it is evident that stems and fleshy fruits have somewhat lower K+ concentrations than other organs. Also, roots reflect the K+ nutritional status of plants, and those insufficiently supplied with K+ have extremely low K+ concentrations. Young roots well supplied with K+ have even higher K+ concentrations in the dry matter than well-supplied leaves (see Table 4.5). The K+ concentrations for mature kernels of cereals including maize ranges from 4 to 5.5mg/g, for rape seed from 7 to 9mg/g, for sugar beet roots from 1.6 to 9mg/g, and for potato tubers from 5 to 6mg/g.

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