Potassium uptake by potatoes

SUMMARY Potatoes (var. Pentland Dell) were grown in pots containing soils from the Bothamsted ley–arable experiments. When about half the initially available K was used, the tops were harvested and the potential limiting K uptake, inferred from K uptakes, was – 4150 cals/equiv. The plants grew on until they exhausted the available K and died, having set tubers. The potential then limiting K uptake, inferred from total K uptakes, was – 4900 cals/equiv., similar to the mean potential in the exhausted soils, – 4710 ± 61 cals/equiv. The significance of these measurements is discussed. Total K uptake was closely related to the amount of K that had to be removed from each soil to lower the potential to – 4900 cals/equiv. and the relationship suggested that the potatoes did not use any K from initially non-available reserves. Dry-matter yields of tubers and of tops + roots, and the ratio of the two, were well related to quantity and potential of K in the soil; tuber yield was also well related to K in tops. The K potential needed for maximum yield of tubers exceeded – 2430 cals/equiv.