مجله پژوهش آب در کشاورزی
سال سی و ششم شماره 2 (تابستان 1401)

This project was implemented with the aim of measuring water applied to onion under farmers’ management in 190 selected sites at the production hubs of onion in Iran including Azarbaijan Sharghi, Isfahan, Khusestan, Zanjan, Kerman, Fars, Khorasan Razavi, Khorasan Shomali, and Hormozgan provinces. According to the results, differences between the average volumes of irrigation water in those provinces, different irrigation methods, various sources and salinities of irrigation water and soil, and different onion varieties were significant (p<1%), during the growing season of 2020-2021. The average amount of applied water by farmers in those provinces was 9502, 13273, 9740, 16588, 9618, 13880, 11998, 8438 and 7057 m3/ha, respectively, with the weighted average of 10823 m3/ha. The onion yield in selected sites, varied from 20000 to 90000 kg/ha, with an average of 49980 kg/ha. The measured values were compared with the net irrigation water requirement estimated by the FAO Penman-Monteith method and with the National Water Document values. The results showed that the differences between average volumes of applied water by farmers, yield and irrigation water productivity, and irrigation water plus effective rainfall productivity in the selected sites were significant at 5% probability level. Irrigation water productivity varied from 3.13 to 6.30 kg/m3 and its average was 4.93 kg/m3. The average irrigation water plus effective rainfall productivity for onion in Iran was 4.50 kg/m3. The average net irrigation water requirement in the study areas by the Penman-Monteith method and the National Water Document were 8834 and 6972 m3/ha, respectively. These results showed that the average applied water in surface, sprinkler, and drip irrigation methods were 11453, 12740 and 10317 m3/ha, respectively, with significant (p<5%) difference. These results showed that in drip irrigation method, applied water was 10% lesser while irrigation water plus effective rainfall productivity was 35% higher. Transplanting seedling compared to direct seeding caused 14.7% reduction in applied water and 16.7% increase in water productivity. According to the results of this study, drip irrigation and transplanting method for onion fields is recommended.

The current research was conducted with the aim of identifying the weaknesses, strengths, threats, and opportunities in the operation of the Dasht Varamin Network from the viewpoint of users, experts, and managers of the network. The research tool was a questionnaire whose validity was improved by completing 30 prototypes and checking reliability under the supervision of university professors, managers, and experts in this field. Data was collected by single-stage, random, and field survey. The statistical population included the network operators, experts, and active managers. The statistical sample size was 98 through the Cochrane relationship and 105 to avoid errors. The results of the SWOT analytical model showed that with increasing information and real awareness of the users about the challenges of the network, the cost of construction and maintenance, the actions of the Irrigation Department and Water Affairs, Agricultural Jihad, and other related organizations, will encourage the users to stop confronting and having a negative attitude. Thus, they would probably have a more responsible and concerned participation and would take more effective steps in order to remove the threat, eliminate the weakness, enhance the strength, and use the opportunities. The comparative examination of the opinions of experts such as users determined opportunities more than threats, weaknesses and strengths, this shows a shared view and hope for the existing opportunities of the network. From the respondents’ point of view, the priority was to determine the competitive strategies, then, the defensive ones. Knowing the problems of the users (challenge of the administrative process, inconsistency of the sectors related to water, negative view of the government measures by considering the previous unsuccessful experiences) experts can eliminate the weaknesses and threats in order to facilitate the affairs for the water users. Activities such as promoting new methods of irrigation and agriculture and showing the successful experiences of cooperative management of water users in the network, should have pioneering and practical results.

In order to investigate the effect of different irrigation systems and weed control treatments on quantitative and qualitative yield of sugarcane and weeds biomass, an experiment was conducted as split plot based on randomized complete block design (RCBD) with three replications in 2020 at Sugarcane Development Research and Training Institute of Khuzestan, Iran. The five irrigation systems included surface drip irrigation (I0), two types of subsurface drip irrigation with a discharge rate of 2.3 and 3.6 L/h and emitter spacing of 50 and 60 cm (I1 and I2 respectively), Low Energy Precision Application (LEPA) sprinkler irrigation (I3), and the conventional  furrow irrigation method (I4) as the main plot, and weed treatments included no weed control throughout the season, (W0), weed control throughout the season (W1), and use of cultivator (W2). The highest and lowest mean cane yield (167 and 117 ton/ha, respectively) and sugar yield (18.24, 12.40 ton/ha, respectively) were observed in I3 and I4 irrigations, respectively. Mean cane and sugar yield in W0 were significantly lower than W1 and W2 treatments (with a difference of 18.34% and 18.78% for cane yield and 17.84% and 18.85% for sugar yield, respectively). Qualitative traits including Brix, syrup sucrose percentage and syrup purity percentage were not affected by irrigation systems and weed control treatments. The total dry matter of weeds for I0, I1, I2, I3 and I4 Irrigation treatments were 90, 78, 47, 43 and 173 g/m2 under W0 treatment and 30, 23, 16, 15 and 40 g/m2 under W2 treatment, respectively. In the condition of the study area, results indicated that adoption of LEPA sprinkler or subsurface drip irrigation system together with the use of cultivator in the first ratoon leads to irrigation water saving and reduces weeds competition in sugarcane fields.

In this study, the seasonal applied water and physical and economic water productivity of soybean were evaluated through monitoring 37 farmers’ fields (with furrow/border irrigation systems) in Moghan Plain, Ardabil Province, Iran, during the 2020-21 growing season. The net soybean water requirement during that growing season and its 10-year mean value ranged from 431-691 mm and 442-671 mm with a mean of 542 and 543 mm, respectively. The mean seasonal total applied water (irrigation + effective precipitation) and the grain yield were 6554 m3 ha-1 and 2.90 ton ha-1, ranging from 5005-10009 m3 ha-1 and 2.05-4.12 ton ha-1, respectively. The mean seasonal total applied water for spring soybean (7906 m3 ha-1) was significantly (P < 0.01) higher than its corresponding value for summer soybean (6390 m3 ha-1). Total water productivity (WPI+Pe) and economic water productivity (WP$) ranged from 0.18 to 0.30 kg m-3 and 15.21 ´ 103 to 62.40 ´ 103 Rials m-3 with a mean of 0.24 kg m-3 and 33.19 ´ 103 Rials m-3, respectively. In most of the studied farms (70% of total cases), the grain yield was higher than the minimum expected threshold for irrigated soybean (2.5 ton ha-1). The results indicated that reasonable levels of grain yield and water productivity indices can be achieved by applying five and three irrigations for spring and summer soybean, respectively. The mean water application efficiency over soybean growth stages in the studied fields ranged between 50-82%.

This study aimed to determine the crop coefficient of sugar beet using canopy cover extracted from digital images under different irrigation managements. The crop coefficient and canopy cover were directly measured by water balance and image processing methods, respectively, in 10 days intervals during the growing season. The crop coefficient of sugar beet in three irrigation managements with maximum allowable depletion (MAD) of 40%, 60%, and 80%, was estimated using its regression equation with canopy cover. This was modeled for potential conditions and then validated by using the average measurements in two years. The findings showed that the estimated crop coefficients were in good agreement with the observations in irrigation managements that had MAD of 40% and 60%. The coefficient of determination (R2), normalized Root Mean Square Error (nRMSE), and model efficiency (EF) were 0.95, 0.11 and 0.95, for 40% MAD, 0.9, 0.13 and 0.85 for 60% MAD, respectively. The results illustrate that the crop coefficient of sugar beet, within the moisture range between field capacity to a MAD of 60%, can be reliably estimated by this approach. The values of determination coefficient (R2), normalized Root Mean Square Error (nRMSE) and model efficiency (EF) decreased to 0.49, 0.37 and 0.63, respectively, for 80% MAD, indicating poor performance of the model under severe drought stress conditions. The proposed method has some advantages including easy and fast data collection, greater accuracy and lower cost, the ability to provide the desired number of images, and no need for meteorological data. Therefore, this can be applied to study the plant growth and crop coefficient variations during the growth period.

In the present study, the effect of different levels of water and salinity stresses was investigated on dry matter production, biochemical attributes, and activity of antioxidant enzymes in sorghum [Sorghum bicolor (L.) Moench] in Marvdasht and Arsanjan regions in 2017. The treatments included four levels of water stress: 100%, 85%, 70%, and 55% of field capacity (FC) in the main plots and four levels of salinity stress: 1.5, 4.5, 7.5 and 10.5 dS m-1 in the sub plots, which were arranged in split plots based on randomized complete block design, with three replications. The results showed that water and salinity stresses in both regions were associated with decreased dry matter production and concentrations of chlorophylls a and b and carotenoids, while the concentration of free proline and the activity of antioxidant enzymes catalase, peroxidase and superoxide dismutase were increased depending on the stress level. Ascorbic peroxidase activity was increased only under water stress. The highest dry matter yields were obtained from 100% FC irrigation with 4.5 dS m-1 salinity and were 1.292 and 1.198 kg ha-1 in Marvdasht and Arsanjan, respectively. Non-significant effect in 85% FC irrigation regime showed that only 70% and 55% FC irrigation regimes led to water stress in sorghum. On the other hand, no significant difference was observed between non-saline conditions and 4.5 dS m-1, which indicates salinity tolerance of sorghum, at least up to this level. In both regions, the intensity of changes due to water and salinity stress was correlated with the intensity of that stress. The results of this research showed that due to antagonistic effects, drought and salinity stresses have a greater effect on reducing plant yield; therefore, water deficit irrigation strategies are not recommended in case of using water with salinities of 7.5 dS m-1 and more for sorghum irrigation.

For irrigation planning, parameters such as actual crop water needs (transpiration) and water losses (evaporation) are considered. In this research, for management of deficit irrigation, the amounts of maize evapotranspiration components were simulated under water stress conditions. Water stress was applied by reducing the soil water, relative to the readily available water. Four treatments were defined as depletion of the available soil water by 40% (I0), 55% (I1), 70% (I2), and 85% (I3). The amounts of maize evapotranspiration and its components (transpiration and evaporation rates separately) were measured in a mini-lysimeter. The seasonal total values of evapotranspiration and components of transpiration and evaporation were equal to 443, 319 and 124 mm (I0), 401, 282 and 119 mm (I1), 303, 211 and 92 mm (I2), and 201, 127 and 74 mm (I3), respectively. Soil water deficiency reduced the evapotranspiration and its components relative to the normal conditions (treatment I0). Reduction of evaporation losses was favorable point in this deficit irrigation method (long irrigation interval). Transpiration and evaporation values were simulated based on the evapotranspiration data (in I0), evapotranspiration stress coefficient (Ks), and crop growth stage sensitivity (Kpi). For this purpose, we used the linear, exponential, logarithmic, polynomial, and power functions as the regression models. By using the actual data, unknown coefficients in the functions were estimated by SPSS software and regression models were generated. Statistical analyses showed that the linear function (R2= 0.91) and polynomial function (R2= 0.874) were the optimal models for estimation of transpiration and evaporation components (under water stress conditions), respectively. The actual water requirement of crop and evaporation losses can be estimated more accurately by separate estimation of evapotranspiration components. This would provide a suitable criterion for irrigation planning and calculation of water use efficiency.