DYNAMICS OF NUTRIENT-UPTAKE FROM FOLIAR FERTILIZERS IN RED RASPBERRY (RUBLES-IDAEUS L)

The dynamics of nutrient uptake from foliar applied N-15-urea and Rb ( a K analog) were quantified in red raspberries. Both N and Rb in an aq ueous solution were absorbed rapidly into the leaf and transported thr oughout the plant. In the greenhouse, about half of the urea and a thi rd of the Rb were absorbed within 32 hours of application. The additio n of a surfactant to the foliar solution reduced uptake, while solutio n pH, time of application and leaf age had little effect. The lower le af surface exhibited a faster rate of absorption than the upper surfac e, but the difference was not large. In the field, some foliar N appea red to have been washed off leaves and taken up by the root system; ho w ever, none of the foliar applications affected plant growth. We conc lude that significant uptake of foliar applied N and K occurs in raspb erry, but the absolute amount delivered through a single foliar applic ation is small, The percentage of total plant nutrient supplied throug h a foliar application is reduced to <5% over time as the plant grows, so multiple applications would be required to maintain levels signifi cantly higher than would exist through root uptake alone.