Contribution of Evapotranspiration Reduction during Sprinkler Irrigation to Application Efficiency

The effect of reduced corn evapotranspiration (ET) during solid-set sprinkler irrigation on application efficiency was analyzed on two subplots. During each irrigation event, one subplot was irrigated (moist treatment) while the other was not (dry treatment). ET (weighing lysimeter) and transpiration (heat balance method) rates were determined at each subplot before, during, and after the irrigations. During daytime irrigations, there was a significant decrease in ET (32–55%) and transpiration (58%) for the moist treatment. After the irrigations (1–2?h), ET significantly increased (34%) and transpiration decreased (20%). Gross wind drift and evaporation losses (WDELg) were found to be 19.3% of the applied water. Taking into account the ET changes during and after the irrigations, net sprinkler evaporation losses (SELn) were 14.4–17.5% of the applied water. During nighttime irrigations, changes in ET and transpiration were almost negligible, and SELn were slightly greater than WDELg (9.5 and 8.1%, respectively, of applied water). SELn was mainly a function of wind speed. Reduced ET and transpiration during daytime irrigations moderately increased solid-set sprinkler application efficiency.     

Applications of Drag-Reducing Polymers in Sprinkler Irrigation Systems: Sprinkler Head Performance

The study investigates the effects of polymer additives on sprinkler performance. Experiments were carried out on a medium-pressure sprinkler to determine the effect of polymer additives. Two kinds of polymer additives with several concentrations were used: a low molecular weight polymer, sodium carboxymethylcellulose, and a high molecular weight polymer, polyacrylamide. The results show that with polymer additives the radius of throw and the sprinkler flow rate increase. The jet is slightly affected. Generally, polyacrylamide shows better results than sodium carboxymethylcellulose.     

Optimal Design of Pressurized Irrigation Subunit

A linear programming (LP) model is presented for optimal design of the pressurized irrigation system subunit. The objective function of the LP is to minimize the equivalent annual fixed cost of pipe network of the irrigation system and its annual operating energy cost. The hydraulic characteristics in the irrigation subunit are ensured by using the length, energy conservation, and pressure head constraints. The input data are the system layout, segment-wise cost and hydraulic gradients in all the alternative pipe diameters, and energy cost per unit head of pumping water through the pipeline network. The output data are: segment-wise lengths of different diameters, operating inlet pressure head, and equivalent annual cost of the pipeline network. The explicit optimal design is demonstrated with design examples on lateral and submain or manifold of pressurized irrigation systems. The effect of the equations for friction head loss calculation on optimization procedure is investigated through the design example for microirrigation manifold. The performance evaluation of the proposed model in comparison with the analytical methods, graphical methods, numerical solutions, and dynamic programming optimization model reveals the good performance of the proposed model. The verification of operating inlet pressure head obtained by the proposed model with accurate numerical step-by-step method suggested that it is mostly accurate.     

Method for Measurement of Canopy Interception under Sprinkler Irrigation

A procedure called water wiping is developed to measure the amount of water intercepted by the canopy of winter wheat under sprinkler irrigation. Macromolecule bibulous materials with high water absorption is used to collect sprinkler water intercepted by winter wheat canopy by wiping water from leaves, sheathes, heads, and stems. A procedure is developed for application and verified using field experiments. The results show that this method is rational and applicable. This method could be used to measure canopy interception of other crops with small leaves and short heights.     

Operational Cost Benefits Study of Flexible On-Farm Irrigation Supply Systems

Efficient on-farm use of water and labor for all methods requires a water supply flexible in frequency, rate, and duration and under the control of the irrigator at the point of application. For surface irrigation, the use of large capacity systems for supply and distribution are essential and economical, especially when considering the reduced labor needs, increased irrigation efficiency, and reduced potential high water table problems resulting from having a large, flexible supply associated with a flexible arranged-demand schedule. Automation and stability of flow at the farm turnout, comparable to a domestic system with variable flow delivery conditions, are typically accomplished by use of large capacity semiclosed pipeline systems. A cost comparison of capital investment for various sized, flexible supply systems with resulting farm water and labor costs is presented which shows the great value from the upgraded management made possible.     

Water Stress Detection Under High Frequency Sprinkler Irrigation with Water Deficit Index

A remote sensing package called the agricultural irrigation imaging system (AgIIS) aboard a linear move irrigation system was developed to simultaneously monitor water status, nitrogen status, and canopy density at one-meter spatial resolution. The present study investigated the relationship between water status detected by AgIIS and soil moisture for the 1999 cotton (Gossypium hirsutum, Delta Pine 90b) season in Maricopa, Ariz. Water status was quantified by the water deficit index (WDI), an expansion of the crop water stress index where the influence of soil temperature is accounted for through a linear mixing model of soil and vegetation temperature. The WDI was best correlated to soil moisture through the FAO 56 water stress coefficient Ks model; stability correction of aerodynamic resistance did not improve correlation. The AgIIS did provide field images of the WDI that might aid irrigation scheduling and increase water use efficiency.     

Survey of Irrigation Methods in California in 2001

Reliable information on irrigation methods is important for determining agricultural water demand trends. Therefore, a study was conducted during 2002 to collect information on irrigation methods that were used by growers to irrigate their crops in 2001. The results were compared to earlier surveys to assess trends in cropping and irrigation methods. A one-page questionnaire was developed to collect information on irrigated land by crop and irrigation methods. The questionnaire was mailed to 10,000 growers in California that were randomly selected from a list of 58,000 growers by the California Department of Food and Agriculture, excluding rice, dry-land, and livestock producers. From 1972 to 2002, the area planted has increased from 15 to 31% for orchards and from 6 to 16% for vineyards. The area planted to vegetables has remained relatively static, while that planted to field crops has declined from 67 to 42% of the irrigated area. The land irrigated by low-volume (drip and microsprinkler) irrigation has increased by about 33%, while the amount of land irrigated by surface methods has decreased by about 31%. Sprinkler usage has decreased in orchards and vineyards, but it has increased in vegetable crops.     

Hydrologic Impacts due to Changes in Conveyance and Conversion from Flood to Sprinkler Irrigation Practices

Improvements in irrigation efficiency are well documented when changing from flood to sprinkler irrigation methods; however, other impacts to the watershed associated with this change are not well known. The resulting impacts to a river basin hydrology when irrigation and conveyance methods are changed are the focus of this study. In an attempt to improve water application and conveyance efficiencies in the Salt River Basin of western Wyoming, irrigation practices were changed from flood irrigation to sprinkler irrigation beginning in the late 1960s, with completion by the mid-1970s. Based upon a water balance, flow in the Salt River increased an average of 65.62 MCM/year. Return flow timing was also impacted by the conversion to sprinkler irrigation. Flows increased 34% in May and 50% in June, while decreasing 15 and 14% in August and September. These changes may have coincided with decreases in groundwater storage. However, analysis of changes in groundwater levels with time was inconclusive. Surface water total dissolved solids (TDS) appears unaffected by the conversion in irrigation practices, while limited groundwater quality data indicate that TDS values are lower in sprinkler irrigated areas.     

Measurement Accuracy Analysis of Sprinkler Irrigation Rainfall in Relation to Collector Shape

Sprinkler irrigation is a widely studied subject in scientific and technical literature. Initially studies were mainly conducted experimentally, whereas more recently we can say that the use of simulation models is the rule. To calibrate such models, experimental data of high precision are required to prevent possible errors in simulations. In sprinkler irrigation evaluation the collectors play a central role and should be designed to minimize the perturbation of water application it is measuring. Using the fluid dynamics software program Fluent, several designs of collectors have been analyzed to assess their capabilities for precise water collection under a horizontal wind. The analysis was performed in two steps: (1) evaluation of airflow perturbation due to collector and (2) calculation of collection rate for different droplet diameters and wind velocity on two selected collectors (one minimizing airflow perturbations, one easy to manufacture). The collector design producing the best results was used to create a mold for manufacturing collectors out of injected plastic material.     

Evaluation of Closed-Loop Site-Specific Irrigation with Wireless Sensor Network

Automated site-specific sprinkler irrigation system can save water and maximize productivity, but implementing automated irrigation is challenging in system integration and decision making. A controllable irrigation system was integrated into a closed-loop control with a distributed wireless in-field sensor network for automated variable-rate irrigation. An experimental field was configured into five soil zones based on soil electrical conductivity. In-field soil water sensors were installed on each zone of the distributed wireless sensor network and remotely monitored by a base station for decision making. The soil water sensors were calibrated with a neutron probe and individually identified for their response ranges at each zone. Irrigation decisions were site-specifically made based on feedback of soil water conditions from distributed in-field sensor stations. Variable-rate water application was remotely controlled by the base station to actuate solenoids to regulate the amount of time an individual group of sprinkler nozzles was irrigating in a 60-s time period. The performance of the system was evaluated with the measurement of water usage and soil water status throughout the growing season. Variable water distribution collected in catch cans highly matched to the rate assigned by computer with r2 = 0.96. User-friendly software provided real-time wireless irrigation control and monitoring during the irrigation operation without interruptions in wireless radio communication.     

Comparison of Different Irrigation Methods Based on the Parametric Evaluation Approach in Abbas Plain: Iran

The main objective of this research is to compare different irrigation methods based upon a parametric evaluation system in an area of 29,300 ha in the Abbas plain located in the Elam Province, in the west of Iran. The soil properties of the study area such as texture, depth, electrical conductivity, drainage, calcium carbonate content, and slope were derived from a semidetailed soil study carried out on the Abbas Plain on a scale of 1:20,000. Once the soil properties were analyzed and evaluated, suitability maps were generated for surface, sprinkle, and drip irrigation methods using remote sensing techniques and geographic information system. The obtained results showed that for 16,125 ha (55.03%) of the study area surface irrigation method was highly recommended; whereas for 16,600 ha (56.66%) of the study area a sprinkle irrigation method would provide to be extremely efficient and suitable; moreover, it was found that 15,425 ha (52.65%) of the study area was highly suitable for drip irrigation methods; however, one soil series coded 9 and covering an area of 2,150 ha (7.34%) was incompatible for sprinkle and surface irrigation systems. For drip irrigation systems the unsuitable lands did not exist in this zone. The results demonstrated that by applying sprinkle irrigation instead of surface and drip irrigation methods, the arability of 21,250 ha (72.53%) in the Abbas Plain will improve. In addition by applying drip irrigation instead of surface and sprinkle irrigation methods, the land suitability of 6,275 ha (21.42%) of this plain will improve. The comparison of the different types of irrigation techniques revealed that the sprinkle and drip irrigation methods were more effective and efficient than the surface irrigation methods for improving land productivity. It is of note, however, that the main limiting factor in using either surface and/or sprinkle irrigation methods in this area is soil texture and the main limiting factor in using drip irrigation methods were soil calcium carbonate content and soil texture.     

Improved Pressurized Pipe Network Hydraulic Solver for Applications in Irrigation Systems

GESTAR is an advanced computational hydraulic software tool specially adapted for the design, planning, and management of pressurized irrigation networks. A summary is given of the most significant characteristics of GESTAR. The hydraulic solver for quasi-steady scenarios uses specific strategies and incorporates several new features that improve the algorithms for pipe network computation, overcoming some of the problems that arise when attempting to apply drinking water software, using the gradient method, to irrigation systems. It is shown that the gradient method is a nodal method variant, where flow rates are relaxed using head loss formula exponents. Although relaxation produces a damping effect on instabilities, it is still unable to solve some of the numerical problems common to the nodal methods. In this contribution the results of the research on computational strategies capable of dealing with low resistance elements, hydrant modelling, multiple regulation valves, numerous emitters, and pumps with complex curves are presented, obtaining accurate results even in conditions where other software fails to converge. GESTAR incorporates all these computational techniques, achieving a high convergence rate and robustness. Furthermore, GESTAR’s solver algorithm was easily adapted to incorporate inverse analysis options for optimum network control and parameter calibration. Illustrative examples are provided, documenting the improved numerical techniques and examples of GESTAR’s performance in comparison with EPANET2, a widely used gradient method-based hydraulic solver.     

Economic Design of Center-Pivot Sprinkler Laterals

Center-pivot laterals are characterized by important friction loss, so therefore the energy consumption is also significant. In this paper, a new, particularly simple, equation is derived to solve explicitly the economic design problem of tapered center-pivot laterals taking into account the energy cost. The appropriate lengths of center-pivot lateral segments with different pipe sizes are calculated directly from the proposed equation in such a way that the total cost of energy and lateral segments is minimized. Friction loss can be calculated using the simple empirical Hazen–Williams formula but also can be calculated using the more general Darcy–Weisbach friction equation. The explicit economic design is applied in two design examples. A detailed economic analysis and comparison between different systems with and without multiple pipe lateral sizes also is performed. A stepwise economic design method determining the most economic pipe diameter at each section of the lateral included between two consecutive sprinklers also is applied. Comparison between the two methods indicates the good performance of the analytical method.     

Allocation of Flow to Plots in Pressurized Irrigation Distribution Networks: Analysis of the Clément and Galand Method and a New Proposal

This article reviews the method for allocating flow to irrigation plots proposed by Clément and Galand in (1979). Mention is made of its shortcomings, such as the lack of consideration given to the specific technical and economic factors governing current pressurized (drip or sprinkler) irrigation systems and how they provide water to plots. We propose a method for fixed irrigation systems, which takes into account the irrigation method on the plot and the existence of an optimum block area. The result is to allocate a constant flow of water to plots up to an established value of maximum surface area. From there on, we propose applying linear increases related to the total plot area. We also present a formula for calculating the maximum number of blocks based on variables that are easily obtainable during the project phase.     

Hydraulic Analysis of Multidiameter Center-Pivot Sprinkler Laterals

Analytical equations for direct hydraulic analysis of a multidiameter center-pivot lateral with and without an end gun were developed. The pressure head profile along the multidiameter center-pivot lateral is described by simple analytical functions. The analysis is based on both continuous outlet and discrete outlet approaches. Friction losses can be calculated using the Darcy–Weisbach or the Hazen–Williams formulas. The proposed equations simplify important practical applications such as the economic design and evaluation of a multidiameter center-pivot system. A comparison test with a numerical stepwise method indicates that the proposed analytical approach is sufficiently accurate for practical applications.     

Coupled Crop and Solid Set Sprinkler Simulation Model. I: Model Development

The development of a coupled crop model (Ador-Crop) and solid set sprinkler irrigation model (Ador-Sprinkler) is reported in this work. The crop model incorporates many of the features developed in the well-known CropWat model. Improvements include the use of thermal time and the input of daily ET0. The solid set sprinkler model applies ballistic theory to determine water distribution resulting from water droplets subjected to a wind vector. Regarding the validation of the coupled model (AdorSim), the plot of soil available water versus measured and simulated yield reduction resulted in similar features. AdorSim explained 25% of the variability in measured yield reduction. Most of the unexplained variability is due to the effect of nonwater-related factors affecting crop yield. In a companion paper, AdorSim is used to investigate optimum water management options in the middle Ebro basin in the NE of Spain.     

Coupled Crop and Solid Set Sprinkler Simulation Model. II: Model Application

In this work, applications of the coupled solid set sprinkler irrigation and crop model AdorSim introduced in the companion paper are presented. The sprinkler irrigation model is based on ballistic theory, while the crop model is based on CropWat. AdorSim was used to evaluate the effect of sprinkler spacing on seasonal irrigation water use (WU) and crop yield. The most relevant results were related to the characterization of advanced irrigation scheduling strategies. The differences in crop yield and WU derived from irrigating at different times of the day were estimated for two locations strongly differing in wind speed. Irrigation guidelines were established in these locations to relate gross water use and water stress induced yield reductions. Simulations were also applied to estimate adequate wind speed thresholds for irrigation operation. In the experimental conditions, thresholds of 2.0–2.5?m?s?1 proved effective to control yield reductions and to minimize WU.     

Quantifying Management of Irrigation and Drainage Systems

To evaluate the performance of irrigation systems, different indicators have been used by researchers. In this study some of the water management problems of three different irrigation systems in Iran are presented. In addition, the water delivery performance of the Doroodzan Irrigation and Drainage Network in southern Iran is evaluated in detail. The analyses included wet and dry seasons and were based on the indicators of overall project water delivery efficiency (ep) and the monthly water requirement of crops. The distribution and conveyance of water in the Doroodzan Irrigation Network was unreliable in both seasons. With an overall project efficiency of around 46%, about 20% of the total delivered water was distributed unreliably. Water distribution equity along tertiaries was also found to be poor. A contributing factor could be the poor operation and maintenance of gates.     

Model for the Simulation of Water Flows in Irrigation Districts. I: Description

Significant improvements in the profitability and sustainability of irrigated areas can be obtained by the application of new technologies. In this work, a model for the simulation of water flows in irrigation districts is presented. The model is based on the combination of a number of modules specialized on surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balances. These modules are executed in parallel, and are connected by a series of variables. The surface irrigation module is based on a numerical hydrodynamic routine solving the Saint Venant equations, including the heterogeneity of soil physical properties. The simulation of water conveyance is performed on the basis of the capacity of the elements of the conveyance network. Crop growth is simulated using a scheme derived from the well-known model CropWat. The irrigation decision making module satisfies water orders considering water stress, yield sensitivity to stress, multiple water sources, and the network capacity. Finally, the hydrosaline module is based on a steady state approach, and provides estimations of the volume and salinity of the irrigation return flows for the whole irrigation season. The application of the model to district irrigation management and modernization studies may be limited by the volume of data required. In a companion paper, the model is calibrated, validated, and applied to a real irrigation district.     

Model for the Simulation of Water Flows in Irrigation Districts. II: Application

In a companion paper a model for the simulation of water flows in irrigation districts was formulated. The model combines a series of modules specialized in surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balance. The objective of this paper is to calibrate, validate, and apply the model, using the Irrigation District Five of Bardenas (Spain) as a study area. Two years of study were used for the analysis, which could be classified as normal (2000) and dry (2001) from the point of view of crop water requirements. Model calibration was performed in one of the 11 hydrological sectors in which the district is divided. The control variable was the monthly water demand, while the calibration variables were related to irrigation operation and scheduling. The seasonal differences in observed and simulated water demand amounted to 0.9 and 1.9% for 2000 and 2001, respectively. Model validation was performed in the rest of the sectors, and the regression line of observed versus simulated monthly water demand could not be distinguished from a 1:1 line in both years. Model application explored scenarios based on management improvement (controlling the irrigation time) and structural improvement (increasing drainage water reuse for irrigation). These scenarios permitted one to sharply reduce water demand, halve the irrigation return flows, and reduce the daily irrigation period from 24?to?16?h.