Effect of root undercutting time on survival and growth characteristics of Chestnt-leaved Oak bare root 1+0 seedlings under different irrigation period.

Abstract
Background and objectives: Chestnut-leaved oak is one of the most important northern Iran forest trees, that is planted in broad scales in degraded areas of its natural sites. According to deep rooting of Chestnut leaved oak seedlings in nursery bed, root undercutting is inevitable practice in bare root seedlings of this species. Studies showed that late root undercutting in nursery can negatively affect seedling survival and performance in planting site. So far, many efforts were done to determine suitable time of root undercutting in some species of Quercus genus, for example in Lebanon oak and Sessile oak. Because, root undercutting along with growing season can increase drought stress in seedlings and, as a result, can decrease nursery production efficiency, this study aimed to investigate the effect of root undercutting and irrigation period on bare root seedlings of Chestnut leaved oak simultaneously.
Materials and methods: Present study‌ were conducted in Golestan province Ghorogh nursery, so that using a randomized complete-block split-plot design with three replications, effects of root pruning time (pre-summer, late- summer and control) using horizontal blade attached to tractor, and furrow irrigation period (2, 4 and 6 days) on Chestnut-leaved oak bare root seedlings production efficiency and growth characteristics were investigated. At the end of growing season survival and growth characteristics of seedlings were recorded and analyzed using univariate ANOVA and Duncan multiple rage test of means techniques in 0.05% experimental error probability.
Results: The results showed that irrigation period was significantly affected seedlings root dry weight and quality index (QI), so that minimum and maximum amount of seedlings root dry weight were detected in 2 days and 6 days respectively. Also, use of horizontal root undercutting (in different irrigation periods), specially in early summer, significantly increase seedlings root growth trait (volume, length, diameter, area and dry weight) and QI. Furthermore, the result showed that root undercutting in early summer with irrigation period of 6 days is the most suitable treatment for growing Oak seedlings in the study area‌.
Conclusion: Based on this study finding, it can be stated that horizontal root undercutting and irrigation period are essential factors that should be considered in oak seedlings root growth and seedlings quality enhancement practices. Because, the more root system density, extending and frequency, the more nutrient and water absorption potential in seedlings, and such planted seedlings can better resist to harsh environmental condition and establish in forest planting site.