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Using the Williams Equation to Evaluate Nutrient Uptake Rate by Intact Plants

Ben-Gurion Univ. of the Negev, J. Blaustein Inst. for Desert Research, Sede-Boker campus, Israel 84993
Univ. of Arkansas, Agric. Statistics Lab., Fayetteville, AR 72701-1201

^* Corresponding author.

The Williams equation uses root growth and nutrient accumulation data to evaluate nutrient uptake by plants. Accuracy of this equation depends on basic assumptions of constant uptake rate with time and space. The validity of the Williams equation and the assumptions underlying it were tested with sorghum [Sorghum bicolor (L.) Moench] plants grown in solution culture and analyzed for N, P, K, Ca, and Mg uptake. Only N and Ca influx were independent of time, as required by the equation. Influx of P, K, and Mg decreased linearly during the entire growth period. Mean root radius, which is assumed constant, decreased linearly with time. Consequently, a cautious and selective use of the equation is recommended.

Received for publication July 27, 1992.