Potassium and Phosphorus

Abstract

Potassium deficiency was associated with large reductions in the total weight of fruit per vine in a commercial kiwifruit orchard. This effect on yield resulted largely from a reduction in fruit numbers, there being only a slight effect on the mean weight per fruit. There was a strong association between potassium concentrations in leaves collected prior to fruit set and fruit yield. Maximum yields were associated with potassium concentrations in excess of 25 g kg^‐1 DM in the leaves. However, even greater concentrations are likely to be required since there was no indication of the yields diminishing even at this comparatively high concentration. The association was less strong for leaves collected after fruit set. There was no apparent relationship between exchangeable potassium in the soil and the potassium status of the vine.

The postharvest storage of fruit was largely unaffected by potassium deficiency. After 146 days storage at 0.5C to 1C there was no difference in the firmness of the fruit, but the mean soluble solids content of fruit from the severely deficient vines was slightly higher than that from the healthy vines.

Inadequate applications of potassium fertilizer to compensate for potassium required in new cane and leaf growth, and for the large annual removal in fruit, largely accounts for the substantial reductions in yield in this particular orchard.

Key words:

• Potassium deficiency
• kiwifruit (Actinidia deliciosa)
• fruit yield
• postharvest fruit storage