crop water stress index

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.

The presence of salts in irrigation water and high evapotranspiration rate in Sistan and Baluchestan cause the accumulation of salt in the soil and as a result increases the osmotic force in soil. One method for crop irrigation planning is the use of Idso crop water stress index (CWSI) and Moran water deficit index (WDI). In order to investigate the effect of irrigation water salinity on CWSI and WDI and also wheat irrigation planning, an experiment was performed with three different irrigation water quality in Iranshahr, through the 1398-99 crop year. The experiment was performed as a randomized complete block design with 4 replications and 3 treatments including (1) irrigation water with salinity of 0.7, (2) irrigation water with salinity of 2.5 and (3) irrigation water with salinity of 5.2 dSm-1. The results showed that irrigation water with salinity of 0.7 and 2.5 dSm-1 have no significant difference in terms of yield and water use efficiency. However, the use of irrigation water with a salinity of 5.2 dSm-1 caused a significant reduction in yield and water use efficiency at a 1% level. Moreover, the salinity of irrigation water increased the upper baseline in the Idso diagram and the upper side of the proposed trapezoid of Moran, but it had no effect on the baseline (plant transpiration limit under standard conditions). As a result, according to the definition of CWSI and WDI indices, these two indices decreased by 19% and 22%, respectively compared to the control treatment. The average optimal CWSI and WDI in the first (non-saline) treatment were 0.39 and 0.38, respectively, and they were 0.33 and 0.32 in the very saline treatment, respectively. This showed a decreasing trend of irrigation frequency with increasing salinity of irrigation water.

The aim of this study was to assess the crop water stress index (CWSI), derived from leaf temperature using infrared thermometer measurements, to investigate the water stress status and irrigation timing of olive trees. Fpr this purpose a regression function was determined between crop water stress index and relative water content of leaf (RWC) and soil water content (SWC). The experimental treatments involved two olive cultivars (Koroneiki and T2) and four water regimes (irrigation of 100, 85, 70 and 55% of crop water requirement). The results showed that the non-water stressed baseline is varied throughout the study period as well as during the day. The daily variations of non-water stressed baseline were mainly due to variations in the intercept of the non-water stressed baseline that can be explained by variations in zenith solar angle. After investigating the relationship between vapor pressure deficit (VPD) and the difference between crop and air temperature (), the equation of Tc-Ta = -0.45 VPD+1.06, r2 = 0.99 was determined for the non-water stressed baseline of the olive trees at 12:30 pm. The effect of irrigation regime on water stress index of Kroneiki and  olive trees was not significant in none of the measurements during the study period. However, crop water stress index was significantly correlated with relative water content (Kroneiki: r2=0.67**, : r2=0.88**) and soil water content (Kroneiki: r2=0.74**, : r2=0.78**). Therefore, the crop water stress index is a good indicator of the water stress status of the Koroneiki and T2 olive trees.

To investigate the effects of substituting surface drip irrigation (DI) by subsurface drip-irrigation systems (SDI) on plant responses, a10 ha pistachio orchard with DI system located in Shahriar, Tehran province, was selected. Irrigation treatments including DI and SDI with saline water and DI with non-saline water (A) were established and plant responses were measured. The salinity distribution results showed that, in DI, at depth of 30-50 cm and distance of 70-100 cm, salts were accumulated. In SDI, salt accumulation was observed in surface layer and in distance of 60-80 cm from the tree. Based on all plant response indicators, treatment A showed significantly more favorable conditions. Unlike treatment A, there was no significant difference in the “canopy temperature” and “canopy–air temperature difference” between DI and SDI. By normalization of environmental-effects on foliage temperature, crop water stress index (CWSI) showed significant differences between DI and SDI treatments. Also, stomata conductance in SDI was significantly greater than DI. Additionally, treatment A had significantly the highest sap flow (SF). Based on SF measurement in 24 hour, there were no significant differences between DI and SDI irrigation systems, but the mean of this index for daylight time and midday, showed significant differences. With equal depth of irrigation water applied to DI and SDI and more favorable salinity distribution in root zone of SDI, this treatment leads to less water and salinity stress. Although the use of subsurface drip irrigation system requires long-term studies, but in view of the observed plant responses and in terms of soil salinity distribution, it is recommended to use SDI in pistachio trees.

Considering the great value of water, irrigation scheduling, and cultivation of medicinal plants, this research was conducted at the Faculty of Agriculture, Lorestan University, with the aim of scheduling irrigation of summer savory using CWSI and applying different levels of water stress under the condition of pot planting. In this research, seeds of summer savory were cultivated  with three replications under four irrigation treatments of 100%, 80%, 60%, and 40% of readily available water (RAW) (IR100, IR80, IR60 and IR40). Irrigation of the control treatment (IR100) was carried out when all the soil RAW was depleted. Irrigation of the other three treatments was carried out at the same time but with, respectively, 80%, 60%, and 40 percent of the volume applied to IR100.  The canopy cover temperature in IR100 and air temperature (dry and wet) were measured on the day after (8-14 o’clock) and before irrigation (12-15 o’clock) in order to construct the lower and upper limits base lines required to calculate CWSI. According to the result, the upper base line equation is (𝑇𝑐-𝑇𝑎) UL = 0.69, and the lower base line is (𝑇𝑐-𝑇𝑎) LL = 0.2787 - 0.1134 (VPD). Result showed that the effect of water stress on yield was significant. The highest yield was observed in IR100 (1.756 g / plant) and the lowest yield was observed in IR40 (1.421 g / plant). The crop water stress index (CWSI) of the four treatments in the day before irrigation was 0.19, 0.21, 0.28, and 0.46, respectively. According to this information, the permissible CWSI index for irrigation scheduling of summer savory growing in pots was 0.19. The result of means comparison indicated that differences between IR100 and IR80 in values of CWSI and canopy cover temperature were not significant, but they were significant between IR100, IR60 and IR40.  The increment of CWSI in IR80, IR60 and IR40 were 10%, 47%, and 142 percent relative to the IR100. In this research, a strong correlation (r= -0.978*) was obtained between CWSI and stomatal conductance.

Irrigation scheduling under water and salinity stresses is more difficult than normal conditions. To investigate the effect of water stress on crop growth, numerous indices have been introduced which one of them is crop water stress index (CWSI). To evaluate the suitability of this index for irrigation scheduling of corn (maize) with using saline water, a field experiment consisted of irrigation water with five salinity levels (S0: Caroon River (EC= 2.3 dS m-1), S1: EC= . dS m-1, S2: EC=4.5 dS m-1, S3: EC=5.5 dS m-1 and S4: EC=6.5 dS m-1) was conducted at the research station of Shahid Chamran University, Iran. Results showed that the lower baseline equation (without stress) for the summer corn was (Tc-Ta)ll=2.161-0.221 VPD and the upper baseline equation (with full stress) was h=3.690C. The CWSI value as a base for irrigation scheduling was calculated to be 0.23. Also it was found that increasing water salinity caused to increase the foliage temperature. Thus, CWSI may be used for irrigation scheduling under conditions of using saline water. By increasing water salinity from 2.2 to 6.5 dS m-1, the temperature difference between the canopy and air was increased by 30C, approximately. In this research, CWSI values at the day just before the irrigation were 0.23 for S0, 0.35 for S1, 0.46 for S2, 0.58 for S3 and 0.73 for S scenarios. Also results showed by increasing water salinity from 2.3 to 6.5 dS m-1, CWSI increased about three times.