351 Vegetative and Productive Response of Young ‘Williams’ Pear Trees to Regulated Deficit Irrigation (RDI), Mulching and Their Combinations L. Lepaja 1,a , E. Kullaj 1 , K. Lepaja 1 and A. Zajmi 2 1 Department of Horticulture and Lanscape Architecture, Agriculture University of Tirana, Kodër-Kamëz, Tirana, Albania 2 Horticultural Department, Agriculture University of Prishtina, Prishtinë, Kosovë Keywords: canopy volume, water stress, Pyrus communis, evapotranspiration, Kosovo Abstract This field experiment was designed to assess the vegetative and productive response of young ‘Williams’ pear trees to regulated deficit irrigation (RDI), mulching and their combinations with the aim of optimising such parameters. Using a water budged methodology, four levels of irrigation, specifically 100% of ET (control) and deficits of 80, 60 and 40%, were applied to 10 trees, 5 of which were mulched by a 10 cm layer. The experiment was conducted in Kosovo (Dukagjini Plain) during 2013 on a pear orchard of 10 ha in third year using a nested experimental design. Using ANOVA two-way with post hoc testing we found significant changes in a series of vegetative and productive parameters. Irrigation levels significantly influenced leaf surface and area, shoot length, total number of fruit and their weight and consequently total yield. In addition, mulching had a positive effect on all parameter values, in particular on shoot length and fruit diameter during all their growth but more remarkably in the third stage. RDI and mulching had a combined effect on shoot length and canopy volume while changes were not significant for number of leaves, number of shoots, number of fruits of extra class and first class. Considering the young age of trees and long-term consequences of water stress the experiment will be continued. INTRODUCTION Production of pear (Pyrus communis L.) is of particular importance for the economy of Kosovo, of which production in 2012 reached 1562 t. This lack of water can be covered more easily if deficit irrigation (DI) is applied, a technique with plenty of advantages, ranging from water saving, reduction of costs, minimization of nutrient and pesticide leaching to ground water (Pulupol et al., 1996), reduction of excess vegetative growth (Marsal et al., 2002) and quality improvements. DI is a system for the management of soil water to impose periods of water deficit to the plant in such a way as to be economically advantageous. It involves the use of a smaller amount than the calculated need for water (Kullaj, 2007). In other words, DI aims at stabilizing yields and at obtaining maximum crop water productivity rather than maximum yields (Zhang and Oweis, 1999). The use of deficit irrigation control (RDI) is getting more and more used (Goodwin and Boland, 2002; Struthers et al., 2013) in modern orchards and expansion of this technology runs parallel with the method of localized irrigation. In many cases several cultivars are planted within the same orchard and beside different water requirements, similar irrigation rates are applied to these cultivars, reducing the water use efficiency (WUE) (Kullaj et al., 2014). Determination of the age of the tree to start the RDI is highly dependent on genotype and rootstock. Application at an early age leads to an insufficient formation of the crown of the tree while on the other hand the aim is to apply RDI as early as possible. A moderate water deficit modifies the distribution of carbohydrates to the fruit development rather than the vegetation. When calculated over the entire season, RDI trees used 8% less water than well-watered control trees. Lower WU of deficit-irrigated trees was caused primarily by lower stomatal conductance, not by reduced leaf area. Shoot growth could be reduced a lavdim_lepaja@hotmail.com Proc. XII International Pear Symposium Eds.: T. Deckers and J. Vercammen Acta Hort. 1094, ISHS 2015