Iranian Water Research Journal

Iranian Water Research Journal

Investigating the interaction of pruning and water stress on the number of supplementary irrigation times and water productivity of Estahban rainfed fig trees

Document Type : Original Article

Authors
Mohammad Ali Shahrokhnia 1
hamid Zare 2
1 Associate Professor, Agricultural Engineering Research Department, Fars Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Shiraz, Iran
2 Associate professor (Ph.D.), Fig Research Station, Fars Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Estahban, Iran
10.22034/IWRJ.2024.14922.2634
Abstract
Extended Abstract

Fars province is the most important dry fig producing province in Iran, accounting for over 90% of the country's fig production. More than 50% of the cultivated area of rainfed fig orchards in Fars province is located in Estahban region, which includes about 17% of the cultivated figs in the world. In recent decades, decrease in rainfall and drying up of the surrounding lakes have caused water stress in these orchards and loss of some trees. Supplementary irrigation reduces water stress, and pruning fig trees can also reduce the water consumption. In this research, the interaction of different levels of pruning and water stress on fig trees in the Estahban area was investigated.
In this study, three pruning treatments (light pruning, medium pruning, severe pruning) and four water stress treatments (water stress indices of 0.2, 0.4, 0.6 and no irrigation) were considered. This experiment was in the form of factorial with two factors (pruning and water stress index) in the form of randomized complete block design with three replications, at Estahban fig research station. Different levels of water stress index were obtained by measuring the temperature of tree canopy and the air temperature based on past researches. In the current research, the relationships provided by IDSO and previous researchers were used to apply different levels of the water stress index of fig trees. In this method, the difference between the temperature of tree canopy and the air temperature is related to the water stress of the plant. Therefore, based on the different levels of water stress, threshold temperature difference was determined, indicated when irrigation should be applied. Leaf temperature measurements started after the completion of leaf growth and were taken once a week. In order to determine the volume of irrigation water, the soil of the site was sampled and analyzed to measure the moisture content of the field capacity and the wilting point, and the bulk density of the soil. Hence, the volume of irrigation water determined 1500 liter per tree.
The results showed that in the first year, when the amount of rainfall was significantly higher, water stress occurred later in the trees. Water stress treatment with the index of 0.4 required irrigation only in the second year for light and medium pruning level. This treatment did not need a supplemental irrigation under severe pruning conditions. In all three years of the experiment, dry fig trees in the water stress index of 0.6 did not need supplementary irrigation at all three levels of pruning. It can be claimed that with pruning, the number of times of supplemental irrigation of rainfed fig trees was reduced. During the experiments, the amount of yield and water productivity increased, and this increase in yield was significant in the first and third years of the experiment. Also, the difference in water productivity in all three years of the experiment was significant. In different supplementary irrigation treatments, yield values and water productivity were not significantly different, but water productivity increased slightly by reduction in irrigation events. In different levels of pruning, yield values and water productivity did not differ significantly. Therefore, it can be said that pruning, even severe pruning, did not significantly reduce the yield and water productivity of rainfed fig trees. It is clear that the number of supplementary irrigations required by fig trees depends on the amount of water needed or evapotranspiration. That is, the more evapotranspiration, the more irrigation is needed. Moreover, the amount of evapotranspiration is related to the amount of evaporation from the pan in meteorological stations. Therefore, it can be said that the number of times of supplementary irrigation is related to the amount of evaporation from the evaporation pan of the weather station and its difference with the amount of rainfall. A simple linear relationship can be established between the number of times of supplementary irrigation and the difference between evaporation and rainfall. Having these relations, it is possible to predict the number of the supplementary irrigation events according to the difference in evaporation and rainfall. Of course, the mentioned relationships have been extracted according to the limited data obtained from this research. It is evident that increase in data volume leads to increase the accuracy of the extracted relationships.
Keywords
Crop water stress index
Irrigation start time
Irrigation with tankers
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