Abstract
This study was conducted to evaluate the responses of potatoes to six K solution concentrations maintained with a flow‐through nutrient film system. Potato plants were grown for 42 days in sloping shallow trays containing a 1 cm layer of quartz gravel with a continuous flow of 4 ml min‐1 of nutrient solutions having K concentrations of 0.10, 0.55, 1.59, 3.16, 6.44, 9.77 meq L‐1. Plant leaf area, total and tuber dry weights were reduced over 25% at 0.10 meq L‐1 of K and over 17% at 9.77 meq L‐l of K compared to concentrations of 0.55, 1.59, 3.16 and 6.44 meq L‐1 of K. Gas exchange measurements on leaflets in situ after 39 days of growth demonstrated no significant differences among different K treatments in CO2 assimilation rate, stomatal conductance, intercellular CO2 concentration, and transpiration. Further measurements made only on plants grown at 0.10, 1.59, 6.44 meq L‐1 of K showed similar responses of CO2 assimilation rate to different intercellular CO2 concentrations. This suggested that the photosynthetic systems were not affected by different K nutrition. The leaves of plants accumulated about 60% less K at 0.10 meq L‐1 of K than at higher K concentrations. However, Ca and Mg levels in the leaves were higher at 0.10 meq L‐1 of K than at higher K concentrations. This indicates that low K nutrition not only reduced plant growth, but also affected nutrient balance between major cations.