Effect of Planting Dates and Nitrogen Fertilization Rates on Producing Suitable Rootstocks for Grafting of Pistachio (Pistacia vera L.) cv. 'Ashouri'

Abstract

The pistachio tree (Pistacia vera L.) holds significant economic and ecological importance, positioning it as a promising crop for the reclamation of arid and semi-arid lands in the Arab region. However, its slow growth during the early developmental stages presents a major challenge limiting the expansion of its cultivation. Therefore, this study aimed to evaluate the effect of different planting dates and varying rates of nitrogen fertilization on improving the vegetative growth indicators of pistachio seedlings, with the goal of achieving the appropriate size for grafting in the shortest possible time.

An experiment was conducted to investigate the germination of pistachio seeds (local cultivar 'Ashouri') across four successive planting dates at monthly intervals, starting from January 5, 2025. The highest germination percentage (90%) was recorded for the second planting date (February 5), which was also characterized by the shortest period to initiate germination (15 days after sowing). In contrast, the early planting date (January 5) resulted in a significantly lower germination percentage (55%) and a notable delay in germination onset (35 days). The third (March 5) and fourth (April 5) planting dates exhibited moderate germination percentages (65% and 60%, respectively) along with a considerable delay in germination initiation, reaching 40 and 45 days after sowing, respectively.

Regarding the effect of nitrogen fertilization using Diammonium Phosphate (DAP), four application rates (3, 6, 9, and 12 g seedling⁻¹) were applied in addition to a control treatment (no fertilization). The results revealed a significant superiority of the 9 g seedling⁻¹ treatment, which achieved the highest mean seedling height (55 cm) and the largest stem diameter (6 mm). This was followed by the 3 g and 6 g treatments, yielding mean heights of 25 cm and 30 cm, and stem diameters ranging from 3-4 mm, respectively. Conversely, the 12 g treatment exerted a negative effect, resulting in the mortality of five seedlings and reduced mean growth (23 cm height, 2 mm thickness) compared to the control, which recorded the lowest growth metrics (15 cm height, 1.5 mm thickness).

Based on the findings, it is recommended to plant pistachio seeds during the first half of February to achieve optimal germination percentage and rate. Furthermore, the application of Diammonium Phosphate (DAP) fertilizer at a rate of 9 g per seedling is recommended to enhance vegetative growth and attain the appropriate stem thickness, a crucial indicator for successful grafting.