A Method for Measuring Short-Term Nutrient Absorption by Plants: II. Potassium
1959
The method previously reported for measuring short-term P absorption by plants has been adapted to studies of K uptake in relation to various factors. K-deficient oat or corn plants, grown in sand cultures, were placed in contact with soil or soil-fertilizer mixtures for periods of 1 to 14 days. Recovery in oat tops from applications of 10 to 120 mg. K ranged from 25 to 7% in 3 days to 63 to 30% in 14 days. When K content of roots in sand and in soil also was taken into account, 14-day recoveries from 30- and 120-mg. K additions were 85 and 43% respectively. Despite the wide range in K content of plants, growth differences among treatments were not apparent for at least the first week, as had previously been observed in studies with P. Unfertilized soils supplied significant amounts of K to plants in 3 days. At 7 days, rather wide differences in K content of plants were evident among soils, indicating the possible utility of the method in assessing the K status of soils. Moisture contents of soils were important in relation to K uptake. Moisture equivalent for each soil appeared to be the near-optimum level. Availabilities of K in potassium calcium pyrophosphate (KCP), potassium metaphosphate (KMP), and KCl to corn plants were compared in soil and sand. During 1- and 3-day absorption periods, KCl was more available than KMP and KCP in both media. The data suggest that contact with soil increased dissolution of the KMP and KCP. KCl was less available in soil than in sand. Very high correlations were found between uptake of K by tops and whole plants for a wide range of K rates, absorption periods, and soils. Thus, K content of plant tops is a suitable criterion for assessing relative effects of treatments on K nutrition of the plants.
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