Irrigation
H. Ojaghlou; F. Ojaghlou; Mohammad Mahdi Jafari; Farhad Misaghi; Bijan Nazari; Esmaeil Karami Dehkordi
Abstract
Introduction
Over the last years, long-term average rainfall has experienced a meaningful decrease (from 250 to 206 mm per year) leading to continuous drought in Iran. In addition, population growth and increasing demand for food put more pressure on the limited available water resources. Thus, the ...
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Introduction
Over the last years, long-term average rainfall has experienced a meaningful decrease (from 250 to 206 mm per year) leading to continuous drought in Iran. In addition, population growth and increasing demand for food put more pressure on the limited available water resources. Thus, the quantitative and qualitative improvement of agricultural products become a necessity. There is 640,000 hectares of alfalfa cultivated land, standing for 5.4% of the total cultivated area. One of the most basic obstacles in these farms is the unsuitable model of water consumption management. Previous studies were conducted with the aim of evaluating the mutual effects of different treatments in controlled plots. Nonetheless, there is a need for large-scale investigations to monitor and improve water productivity in agricultural systems. In this research, the focus was on irrigation management and optimizing irrigation timing as a potential solution to enhance water productivity, considering the fixed irrigation cycles and traditional use of available water resources. The study began by assessing the current water productivity in 11 alfalfa farms located across four regions in Zanjan province, ensuring a suitable spatial distribution. Subsequently, the impact of irrigation management, particularly the adjustment of irrigation timing, was evaluated to determine its effectiveness in improving water productivity in these farms.
Materials and Methods
Eleven alfalfa farms, covering a total area of 28 hectares, were initially selected in the agricultural lands of Zanjan province. The majority of these farms were equipped with sprinkler irrigation systems. From these 11 farms, two specific farms were chosen to implement the proposed methods aimed at improving water productivity. These selected farms served as experimental sites where the irrigation management techniques were applied and evaluated. Improvement solutions were mainly focused on irrigation management. Each farm was divided into two parts; one part with real conditions (farmers' management) and the second one with controlled conditions. In the controlled treatments, irrigation management was implemented through optimization of irrigation time. A nutritional program was also prepared according to the soil quality of the fields and applied in the controlled treatments. In each farm, basic information such as area, physical and chemical properties of soil and water quality were determined. Irrigation information (such as inflow discharge and irrigation schedule) was measured and determined at least three times during the cropping season. Soil moisture were measured before and after irrigation in order to calculate the water application efficiency. The amount of harvested product and production costs were obtained at the end of the cropping season through measurements and interviews with farmers. In this research, the indicators including the volume of irrigation water, the water use efficiency, and the physical and economic efficiency of water have been calculated to analyze the water productivity.
Results and Discussion
The volume of irrigation water in alfalfa farms was measured as 14250 m3/ha on average (with the lowest and highest consumption values of 9849 and 20576 m3/ha, respectively). The average of irrigation water in farms with surface irrigation systems equals to 17,806 and in farms equipped with sprinkle irrigation systems is about 13,460 m3/ha. While the net water requirement of alfalfa in study area was 7160 to 7290 m3/ha. The minimum and maximum values of water application efficiency were 38.3 and 82%, respectively, with average of 64%. The average of application efficiency in surface and sprinkle irrigation systems were obtained 50 and 67%, respectively. The measured alfalfa yield ranged from a minimum of 6.5 ton/ha to a maximum of 14.1 ton/ha, with an average yield of 10.4 ton/ha. After implementing the revised irrigation program in the controlled plots, the harvested water decreased by an average of 49.5%. It was observed that the irrigation schedule in most farms followed a traditional and estimated pattern, with the depth of irrigation water in the middle of the growing season exceeding the net irrigation requirement. The water use efficiency (WUE) values varied between 0.42 and 1.28 kg/m3, with a minimum value of 0.42 kg/m3 and a maximum value of 1.28 kg/m3. The average WUE was calculated as 0.79 kg/m3. Analyzing the correlation between water consumption and the water use efficiency index revealed a decreasing trend. As the volume of irrigation water increased, the water use efficiency index experienced a decline. Specifically, an increase of 1000 m3 in irrigation water resulted in a decrease of 0.04 kg/m3 in the water use efficiency index. The implementation of the corrected irrigation program and appropriate to the water demand led to an increase of the mentioned index by 72%.
Conclusion
The lack of proper irrigation programs that consider climatic conditions and the actual needs of the alfalfa plant was identified as a key factor contributing to high water consumption in the farms. Additionally, the inefficient selection and design of the irrigation system led to lower irrigation efficiency than expected. Despite the majority of farms being equipped with sprinkle irrigation systems, the harvested water did not decrease significantly due to inadequate water management practices. These factors ultimately resulted in a decline in both physical and economic productivity indicators in the alfalfa farms. However, the results of the study highlighted that implementing corrected irrigation management, particularly through modifications to the irrigation timing, can lead to a significant decrease in volume of irrigation water and an improvement in both physical and economic productivity.
A. Zarei; T. Sohrabi; H. Ojaghlou; Z. Bigdeli
Abstract
Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and ...
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Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and water distribution uniformity. One of the factors affecting the performance of surface irrigation systems is the accurate estimation of infiltration. Due to continuous changes in the infiltration process during on-off cycles in surge irrigation, determining the empirical equation of infiltration in surge irrigation method is complex and requires time-consuming and costly field data. As a result, proper selection and parameterization of empirical equations with a simplified procedure are needed. The goal of this research was the field evaluation of the point method (surge infiltrometer) to simulate the infiltration process in advance phase surges. Materials and Methods: A field experiment was conducted at the experimental station of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. A ring infiltrometer was modified by connecting a pipe arm for inward and outward water flow to the ring and from the ring to the pipe to create on-off surge cycles, respectively. Water entered the ring through the inlet hole at the top of the pipe arm and water depth was recorded at different time intervals during the on-time of each cycle. Four treatments were performed for infiltration tests under surge flow, including different cycle time and ratio. Also, infiltration tests were performed under continuous flow conditions. To simulate the first (dry soil) and second irrigation conditions, infiltration experiments were conducted twice on an 8-day interval. The Kostiakov infiltration equation was corrected by applying surge factors to predict infiltration water depth for subsequent surges, using first surge data. The empirical coefficients of the Kostiakov equation were calculated by applying the two-point technique. Results and Discussion: Results of the study revealed that the infiltration data simulated by the developed Kostiakov equation matched closely with those collected from the surge-ring infiltrometer. The coefficient of determination and the root mean square error were calculated to be 0.92 to 0.97 and 0.03 to 0.16 cm, respectively. In general, the amount of cumulative infiltration in the second and subsequent surges decreased. The ratio of the infiltration depth at the end of the second to the first surge was less than 0.5. In all experiments, the depth of water infiltrated in the third surge was significantly reduced and almost reached to the final infiltration rate. As the cycle ratio increased, the cumulative infiltration also increased. However, the effect of on-off time on the infiltrated water depth in the first experiment was greater than that in the second experiment. It was concluded that in the first experiments, the surging phenomena substantially reduced water movement and the reduction in cumulative infiltration ranged from 50 to 70% during the second surge and from 59 to 85% during the third surge. The above values were determined 52 to 76% and 61 to 88% for the second experiment, respectively. A significant difference was observed between surge and continuous flow tests. The surge flow led to a 46 to 76% reduction in the cumulative infiltration depth compared to the continuous flow. The effect of surge flow was greater in the first experiments. Conclusion: One of the most important points in designing surface irrigation systems is to determine the infiltration equation parameters. In particular, the difficulty involved in the planning and design of surge irrigation systems is the prior knowledge and understanding of how infiltration changes occur during surging. The main objective of the present study was to evaluate the surge ring infiltrometer test to predict the infiltration in the second and third surges using the first surge data. The results obtained from the surge infiltrometer experiments showed that the use of surge irrigation has the potential to reduce infiltration. The observed and predicted cumulative infiltration for the second and third surges showed a good agreement. The surge-ring infiltrometer has the potential for creating an on-off mechanism and is best suited to determine the cumulative infiltration from surges for constant on-off time surge intervals.
P. Moradzadeh; H. Ojaghlou; Mohammad Ghabaei Sough
Abstract
Introduction: The average of irrigation efficiency is less than the global average due to improper irrigation systems and traditional water management practices in the field. The use of modern irrigation systems is one of the most important ways to cope with the water shortage crisis in Iran. ...
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Introduction: The average of irrigation efficiency is less than the global average due to improper irrigation systems and traditional water management practices in the field. The use of modern irrigation systems is one of the most important ways to cope with the water shortage crisis in Iran. However, it is necessary to evaluate the effective factors on performance of irrigation system. In present study, a zoning map of suitable land for implementation of sprinkle irrigation system was prepared using AHP method with considering the criteria such as chemical characteristics of water, soil properties, topography, climate, social and economic factors in the Zanjan plain.
Materials and Methods: The present study was carried out using collected data from Zanjan plain that located in northwest of Iran and east of Ghezel Ozan River. The total study area is about 4705 km2 and the average rainfall and temperature in region are 259 mm and 10.9 °C, respectively. The first step in the AHP method is to create a hierarchical structure. For this purpose, each of the criteria was rated 1 to 9 based on paired comparisons done by experts and then classification maps were prepared for each of them. In order to provide zoning maps for water and soil factors, data of more than 2000 wells and 111 soil samples were collected, respectively. In addition, data of 13 Meteorological stations were used to prepare zoning maps of climatic factors such as wind speed and temperature. In this research, a topographic map with a scale of 1/25000 was used to investigate the ground slope effect. More than 60 interview forms were completed to produce maps related to socio-economic factors. Zoning maps were prepared using the Kriging interpolation method in ArcGIS software. Finally, the weight of each criteria was calculated according to the scores that obtained in the previous stage and then land classification map was produced by applying the obtained weights on each criteria. In order to evaluate the situation of sprinkle irrigation projects, location of 52 farms equipped with sprinkle irrigation system obtained from the agricultural organization of Zanjan province.
Results and Discussion: Regarding the quality of water resources, 40.3% and 21.0% of area were classified in most suitable and suitable classes, respectively and about 10.4% was evaluated in the inappropriate class in order to implementation of sprinkler irrigation. In terms of the soil physical and chemical properties, about 38.4% of plain were classified as "most suitable", 22.8% as "suitable" and 24.7% as "inappropriate" class. In relation to topographic criteria, it can be stated that about 85% of area are in good condition, so that the ground slope in most of the lands is less than 10%. Based on climate criteria and specifically wind speed factor, about 61% of the plain was classified as "good" and "very good", while about 39% was in medium and low class. In terms of social and economic criteria, most of area were found to have a good rating, so there is no particular limitation in this regard. The results of the paired comparisons between criteria showed that, social and climatic criteria have the lowest and highest weight, respectively. The value of the inconsistency rate was calculated about 0.07, which indicated the acceptability of the gained weights. An examination of land feasibility map showed, about 33.4% of the region is suitable for implementing sprinkle irrigation system. About 29.5% and 25.8% were evaluated without limitation and low limitation, respectively. Also, about 10.3% was not recommended for use of sprinkle irrigation. The assessment of the location of implemented projects showed that 44.2% of the projects were in suitable or perfectly suitable classes of land. The rest of the projects (55.8%) were implemented in medium or unsuitable classes.
Conclusion: The results obtained from the AHP method showed that wind speed factor has the most weight and importance in selecting sprinkle irrigation system. Generally, in most farms of the region, there is no significant limitation on the implementation of sprinkler irrigation system. Due to low water quality and high wind speed in a small part of the study area that located in northern and eastern, the use of these systems is not recommended. The results showed that some of the sprinkle irrigation projects have been implemented in lands with low-class and it is essential to improve or change these systems.
