FERTILIZER NITROGEN AND BORON UPTAKE, STORAGE, AND ALLOCATION VARY DURING THE ALTERNATE-BEARING CYCLE IN PISTACHIO TREES

The effects of alternate bearing on recovery and loss of isotopically labeled fertilizer N and B and on the accumulation of carbohydrate and N reserves were assessed in mature 'Kerman' pistachio (Pistacia vera L.) trees. Total recovery of labeled fertilizer N applied once (in lat e January) was almost-equal-to 60 % greater if applied to trees enteri ng an ''off'' than an ''on'' year, with respect to fruiting. Eleven pe rcent more labeled B was recovered in off- than on-year trees. Five ti mes more N (1 vs. 0.2 kg N) was lost from the tree in fruit and senesc ent leaflets from on- than off-year trees. In dormant trees, 144 % and 22 % more starch and N reserves, respectively, were present after off than on years. Thus, on-year trees were characterized by a greater re productive demand for N and carbohydrates, reduced accumulation of C a nd N (i.e., storage) reserves in perennial tree parts, and reduced rec overy of January-applied labeled fertilizer N than off-year trees. As B is absorbed passively, the higher transpiration that may accompany t he 43 % larger leaf area per tree and the probability of increased roo t growth probably contributes to its increased uptake during off years . The enhanced labeled N recovery in early spring by trees entering th eir off year preceded fruit and seed development in on-year trees. The differential tree capacity for nutrient uptake in spring may have bee n conditioned the previous rather than the current year. The increased uptake of labeled N by trees entering an off year (i.e., emerging fro m an on year) was associated with tower levels of carbohydrate and N r eserves than for on-year trees that had just completed an off year. Fu ture experimentation should assess the comparative capacity for nutrie nt uptake by on- and off-year trees at other stages of phenology, e.g. , during seed development and postharvest.