عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Increasing water efficiency and productivity is one of the most important and effective ways to tackle the water crisis and mitigate the effects of drought in agriculture (Hajari-Georgi, 2007). Operation of irrigation (time and depth of water) is determined based on the amount of plant water need. Therefore, to increase the efficiency of irrigationthe crop water requirements have to be precisely estimated. Appropriate management of irrigation water requirements of plants can be achived based on accurate estimates (Farshi and et al., 2003). Among the reasons of errors in estimating crop water requirements are the lack of knowledge of, irrigation designers in agroeconomical issuesand plant physiological characteristics in relation to water consumption and alsochoosing unsuitable methods for estimateing crop water requirements (shahabi and et al, 1383). In drip irrigation systems, local soil or only a portion around the roots of the plants are wet. Irrigation systems and irrigation scheduling can affect water uptake by plants (Michlakis and et al.1996). Using both methods of monitoring soil moisture and weather data simultaneously is needed to estimate the amount of plant needs and irrigation water.
This study used the local irrigation system (bubbler) by monitoring soil moisture and meteorological data to calculate the water requirement of two cultivars of pomegranates (Yazdi and Saveh) and the effect of different irrigation regimes on yield during the growing season. Production in the gardens of four-year pomegranate was examined. Plan was designed on the area of one hectare with sandy loam soil, in a factorial experiment based on randomized complete block It was concluded three treatments (I1, I2, I3), respectively, full irrigation (FC), 25 percent deficit irrigation and 50 percent deficit irrigation, in three replications. Meteorological data required were gained from long-term statistics of synoptic stations weather of Yazd. Evapotranspiration was estimated by Penman-Monteith CropWatt software and calculated during the experiments and their average was used in this study.
In order to analyze and determine the amount of irrigation water and regime in each period, the volumetric soil moisture content by means of reflection from the waves TDR (Model TRIME_FM) were measured.
The amount of water consumed at the end of the growing season in each irrigation regimewas calculated as 3744.44, 2783.1 and 1873.1 cubic meters of water per hectare, respectively for three levels of irrigation (I1, I2, I3). Vriation range in the water need during the growing season was 0.6 to 2.43 mm per day, (I1). Analysis of variance showed that the yield of irrigation regimes I1 and I2 with I3 were significantly different at 5% level. Given the amount of evapotranspiration in each irrigation regime, crop coefficients (Kc) for I1, I2, I3, were 0.54, 0.4 and 0.27, respectively.
According to the results of irrigation water applied to four-year mature trees and trees in full irrigation can be concluded that the age level of the canopy is an important issue in determining the water requirements of the tree. The results showed that the amount of water consumed by fouryear trees comparing to mature trees during the growing season in FC treatments reduce about 6000 cubic meters. Canopy of trees acoording to their age is important in predicting the amount of water used in each of the regimes and causes a large difference in the rate of evapotranspiration. The results showed that with the increase in soil moisture or too much irrigation, the evapotranspiration increased. This reflects the fact that although the pomegranate tree is drought- tolerant, itrequires sufficient water for optimum growth. The lower Kc represents less growth, andsmaller canopy and therefore less amount of ET. The amount of Kc over the growth years shows the sensitivity of the irrigation water requiremen. Pomegranate is a defoliant fruit tree, which has germination and emergence in the spring and leaves fall in the winter. Also, the amount of Kc is very different from season to season (bantana and et al 2010). Changes in water treated in I1 during the growing season were from 0.6 to 2.43 mm per day. The results of variance analysis showed that irrigation levels of I1 and I2 at 5% level had a significant difference with I3. Fainally, due to the lack of water resources, investigating impacts of defecit irrigation in different growth stages is recommended.