INFLUENCE OF THE FOLIAR APPLICATION OF PHOSPHORUS AND POTASSIUM ON THE PHOTOSYNTHETIC INTENSITY IN APPLE TREES (MALUS DOMESTICA BORKH.)

In mature apple trees the influence of the foliar application of the mineral nutrients phosphorus and potassium on the photosynthesis (Pn) of leaves was estimated. The research was performed on twelve-year old trees of the cv. Golden Delicious on M9 rootstock in years 2000 and 2001. The treatments encompassed unpicked or picked trees either sprayed or not with the PK fertilizer Hascon M 10 AD. The photosynthetic intensity was measured in two leaves of short shoots of each tree, five times in year 2000 and at three times in 2001. An influence of PK- fertilizer on photosynthesis of leaves was observed only late in the season (fourth measurement in year 2000). At the third and fifth measurement times trees sprayed with PK and defruited trees showed the lowest Pn. Such differences were evident at 350 ppm of CO₂ (ambient concentration), but were less obvious at 2000 ppm of CO₂ (photosynthetic capacity). The decline in photosynthesis of leaves throughout the season was due to the senescence of leaves. In 2001 effect of PK-sprays was observed, whereas the presence of fruit significantly enhanced photosynthesis one month prior to the commercial picking.