Physiological influence of N in preventing of alternate-bearing of pistachio (Pistacia vera cv. Kalleh-ghuchi)

The physiological influence of N in preventing of alternate-bearing of pistachio (Pistacia vera cv. Kalleh-ghuchi) was studied in the Ghazel Ozen (south-west of Zanjan), Iran, during four years (2003-2006). Nitrogen as urea (CO(NH(2))(2), 46% N) at 100, 150 and 200 g actual N per tree were soil surface applied for both fruiting and non-fruiting of the 25 year-old trees. Floral bud abscission was influenced by the level of N application. It increased, through both in the low N and high N application, as compared to medium (150 g actual N tree(-1)) levels. There was a strong relationship between leaf protein and N application, similarly as leaf protein increased, floral bud abscission decreased. Fresh weight of fruit per tree, as annual yield, was significantly (P = 0.05) influenced by growth season, regardless of N application. "Off" year was the main factor that decreased nut yield (tip to 30%) in control, but fruit quality (nut size, blanked %, protein and fat %) was less affected. The rate of fruit growth (dry weight) varied during fruit growth season for individual treatments. The rate of growth was associated with floral bud abscission, however, as the N application increased, percent of bud abscission decreased. Minerals and protein concentrations in leaves from fruiting branches were in most cases lower than that of non-fruiting ones. The floral bud abscission per cluster was very low during nut fill in "off" year trees compared with "on" year trees, there was a relationship between bud drops and consumption of N (protein concentration of kernel). This indicates that reproductive growth (nut growth) demand more N, especially in the "on" year.