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

Fars province is the most important dry fig producing province in Iran, which accounts for more than 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, the decrease in rainfall and the drying up of the surrounding lakes have caused water stress in these orchards and dead of some trees. Supplementary irrigation reduces water stress, and pruning fig trees can also reduce the water consumption of these trees. 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 of 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 this 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. Based on the different levels of water stress considered, the difference between the temperature of tree canopy and the air temperature on which irrigation should be done was determined. The measurement of leaf temperature started with the completion of leaf growth and was done once a week. In order to determine the volume of irrigation water, once the soil of the test site was sampled and characteristics including the moisture content of the field capacity, the moisture content of the wilting point, and the apparent specific gravity of the soil were measured. Hence, the volume of irrigation water was 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 in question. Water stress index treatment of 0.4 required irrigation only in the second year for light and medium pruning level. In other words, this treatment did not need asupplemental irrigation under severe pruning conditions. In all three years of the experiment, dry fig trees in the water stress index treatment of 0.6 at all three levels of pruning did not need supplementary irrigation. Therefore, in general, it can be said that with pruning, the number of times of supplemental irrigation of rainfed fig trees is reduced. With the passage of time, the amount of yield and as a result the amount of 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 statistically significantly different, but water productivity increased slightly due to reduced irrigation. 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. On the other hand, 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. By having these relations, it is possible to predict the number of times of supplementary irrigation 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 clear that if you have more data, more accurate relationships can be extracted and presented.