Solid Set Sprinkler Irrigation System Research Articles

Analysis of Irrigation Performance of a Solid-Set Sprinkler Irrigation System at Different Experimental Conditions

The complexity of assessing the irrigation performance of a solid-set sprinkler irrigation system implies analyzing factors of the sprinkler features, the spacing among sprinklers, the evaluation heights, the meteorological variables and the crop. In this research, a number of solid-set experiments with impact sprinklers were evaluated with different operating conditions and a number of models of irrigation uniformity (CUC) and losses due to drift and wind (WDEL) were assessed at different catch-can heights. Statistical analysis and predictive models were performed for each variable analyzed. The results showed that ND 5035 and SEN 4023 impact sprinklers that presented the lowest variability in water distributions patterns based on the standard deviations of the irrigation depth collected in the catch can (0.85 mm/h). These sprinklers had demonstrated the best CUC values (mean of 86%) with low WDEL averages (lower than 9%). Regarding the CUC analysis, there was a statistically significant difference in measuring the irrigation uniformity from 1 to 2 m catch-can height based on the analysis of 396 solid-set experiments of different research works. Future research could be focused on more experimental conditions analyzing the effects of the irrigation on the crop agronomic development and its yield.

Effect of Water Regimes and Polyvinyl Alcohol on Faba Bean Yield, Chemical Composition and Water Use Efficiency

Quantifying local crop response to irrigation is important for establishing proper irrigation management approaches.To apply that, a field experiment was carried out to evaluate the effect of three available soil moisture depletion(ASMD) levels, 25 %, 50 %, and 75% applied using solid set sprinkler irrigation system in combination with four concentrations (0.00%, 0.05%, 0.1% and 0.2 %)of poly vinyl alcohol soil conditioner. The combined effect of water regimes and different concentrations of soil conditioner was studied on faba bean (Vicia faba cvGiza 843), The experiment was carried out in the semiarid climate of northeast Farm of El-Ismailia Agricultural Research Station, El-Ismailia Governorate Egypt during two successive seasons(2012/2013 and 2013/2014).Evapotranspiration (ETa), yield productivity of faba bean, water use efficiency and macronutrients uptake were also evaluated. Results showed that the actual seasonal crop evapotranspiration (ETa) for ASMD treatments varied between (1605.36 –2482.45m3 fed-1.) in the first season (2012/2013) and (1439.26 – 2457.01m3 fed-1.) in the second season (2013/2014). There are three options to calculate seasonal ETc for faba bean crop in Ismailia condition. So, it can be use FAO-24RD, PMd or Droogers and Allen (2002)methods. Moreover,obtained data reveal that application of polyvinyl alcohol(PVA)synthetic soil conditioners (with high concentration), decreased available soil moisture depletion (ASMD) in sandy soil and caused a significant increase in faba bean yield, water use efficiency (WUE) and improved the macronutrient uptake by faba bean yield. Finally, the results clearly showed that the significant effect of PVA at (0.1or 0.2 %) concentration was most observed at 50% ASMD.

Site Selection of Different Irrigation Systems Using an Analytical Hierarchy Process Integrated with GIS in a Semi-Arid Region

Site selection of different irrigation systems can lead to higher water productivity in drought conditions. The present study intends to evaluate suitable regions along the Izeh plain (Iran) for different pressurized and gravitational irrigation systems using Analytical Hierarchy Process (AHP) based on Geographic Information System (GIS). To that end, a variety of inputs such as climate, topography, skilled labor and system costs, etc. were identified and classified into two main categories of socio-economic and environmental criteria. Each criterion was subdivided into several criteria to make the site selection more specific. A matrix of the pair-wise comparison was, in turn, used to compare these criteria and sub-criteria, and to evaluate them based on their relative importance based on the region’s suitability for different irrigation system alternatives. Geographical layers were then obtained for each sub-criterion to select the most suitable sites for different irrigation systems in the study area. Pressurized irrigation systems including wheel move irrigation system, drip irrigation system and solid-set sprinkler irrigation system, together with gravitational irrigation systems consisting of surface irrigation system, and low-pressure irrigation system were considered as irrigation system alternatives during the site selection process in this study. The result map of site selection for different alternatives showed that surface irrigation, drip irrigation and low pressure systems were the best irrigation system alternatives for the region studied.

Influence of irrigation time and frequency on greenhouse gas emissions in a solid-set sprinkler-irrigated maize under Mediterranean conditions

Irrigation management may influence soil greenhouse gas emissions (GHG). Solid-set sprinkler irrigation systems allow to modify the irrigation time and frequency. The objective of this study was to quantify the effect of two irrigation times (daytime, D; nighttime, N) and two irrigation frequencies (low, L; high, H) on soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions in a solid-set sprinkler-irrigated maize (Zea mays L.) field located in NE Spain during 2015 and 2016 growing seasons and the fallow period between growing seasons. Compared with D irrigation, N irrigation increased soil water content (0–5 cm) in both growing seasons. Irrigation management did not affect CH4 emissions and the soil acted as a sink of CH4. Cumulative CO2 emissions were affected by the measurement period (growing season vs fallow) with the greatest values in 2015 growing season, being 81 and 32% higher over the fallow period and over the 2016 growing season, respectively, due to the effect of the preceding crop, alfalfa, and a better soil moisture conditions for the microorganism activity. Similarly, cumulative N2O emissions showed the highest values in 2015, reporting values 90 and 51% greater than the fallow period and the 2016 growing season, respectively. Moreover, N irrigation increased cumulative N2O emissions by 29% compared with D irrigation, but irrigation frequency did not affect cumulative N2O emissions. Irrigation time did not affect cumulative N2O emissions scaled per grain yield or per N uptake because N irrigation increased maize yield by 11% compared with D irrigation. Due to the lack of differences in the scaled N2O emissions, N irrigation should be consider as an appropriate strategy to optimize grain yield without compromising soil GHG emissions per unit of grain yield in Mediterranean agroecosystems.

Effects of irrigation uniformity on yield response and production economics of maize in a semiarid zone

Optimized irrigation scheduling to better match applied water to crop requirements can reduce the consumptive use of water and energy, improve water use efficiency, and increase gross profit margin. However, the distribution uniformity of applied irrigation can modify the way reduced water applications influence field-averaged performance, especially for crops sensitive to water stress as maize, in which the most sensitive stages are those related with reproduction and grain formation. We evaluated the effect of irrigation uniformity on the yield and profitability of maize (Zea Mays L.) in Albacete, Spain in two adjacent sectors equipped with a solid set sprinkler irrigation system of a field managed according to FAO-56 methodology throughout the growing season to maximize grain yield without water stress (Sector S1) or irrigation scheduling determined by an experienced producer (Sector S2). Irrigation uniformity was evaluated using catch cans in both fields and grain yield was harvested within zones exhibiting 75% (Z1), 100% (Z2), and 125% (Z3) of area-averaged volume applications throughout the year. The average coefficient of uniformity (CU) in both sectors (S1 and S2) was 83.5%, and the net amount of applied irrigation water totaled 709 mm in S1 and 832 mm in S2. Average grain yield in sector S2 approached the maximum expected yield of 18.4 Mg ha−1 and exhibited no significant differences in yield among zones. In contrast, sector S1 exhibited significant yield differences (p < 0.05) among zones with a measured yield in Z3 of 18.5 Mg ha−1 and a yield reduction of 1.6 Mg ha−1 and 4.0 Mg ha−1 in Z2 and Z1, respectively. Consequently, the area-averaged yield in S1 was 8% less than in S2. This last treatment was positively influenced by a higher amount of irrigation water supplied to the crop (17%), which decreased the effect of low CU (83.5%). The grain yields simulated by MOPECO for each monitoring zone within the sectors exhibited similar magnitude and trends. Because of these yield differences and the relatively low cost of irrigation water, area averaged gross margin in S1 was 18% less compared with S2. Simulations with MOPECO over a range of CU’s demonstrated that improved irrigation uniformity increased area-averaged yields and gross margin when following S1 instead of S2 strategy. The main innovations of this work were to quantify the effect of irrigation uniformity on the gross margin of a maize crop, and to highlight that in arid and semiarid areas with water scarce conditions, it is a better strategy to improve the irrigation uniformity than supply a higher amount of irrigation water to mask the lack of uniformity.

Low-pressure sprinkler irrigation in maize: Differences in water distribution above and below the crop canopy

Reducing the working pressure at the sprinkler nozzles is one of the alternatives to reduce energy requirements in solid-set sprinkler irrigation systems. Previous studies reported ≈10% lower seasonal Christiansen uniformity coefficient (CUC) for low-pressure treatments than for standard treatments, but no differences in maize yield. This research analyses the effect of maize canopy water partitioning on irrigation performance indexes (CUC and wind drift and evaporation losses, WDEL). Three irrigation treatments were considered, based on the working pressure: 1) A standard brass impact sprinkler operating at a pressure of 300 kPa (CIS300); 2) A standard brass impact sprinkler operating at a pressure of 200 kPa (CIS200); and 3) A modified plastic impact sprinkler (with a deflecting plate attached to the drive arm) operating at a pressure of 200 kPa (DPIS200). Irrigation performance was measured using a catch-can network located above the maize canopy (CUCac, WDELac) along the whole crop season and using stemflow and throughfall devices below the maize canopy (CUCbc, WDELbc) in eight irrigation events. Maize growth, yield and its components were measured. Under low-wind and fully developed canopy conditions (a frequent situation for maize irrigation), CUCbc resulted higher than CUCac for the low-pressure treatments, while the opposite was observed for the standard pressure treatment. Maize canopy partitioning reduces the differences in irrigation performance indexes between pressure treatments, explaining why there are no differences in grain yield between them. Caution should be used when measuring sprinkler irrigation performance above tall canopies, since the elevation of the catch-cans and the crop canopy partitioning affect performance estimations.

Fertigation Uniformity under Sprinkler Irrigation: Evaluation and Analysis

In modern farming systems, fertigation is widely practiced as a cost effective and convenient method for applying soluble fertilizers to crops. Along with efficiency and adequacy, uniformity is an important fertigation performance evaluation criterion. Fertigation uniformity is defined here as a composite parameter consisting of irrigation and fertilizer application uniformity indicators. The field and computational procedures for sprinkler irrigation uniformity evaluation have been the subject of various studies. The objective of the study reported in this paper, however, is the development of an analytical framework for the evaluation and analyses of test-plot scale fertilizer application uniformity under solid-set sprinkler irrigation systems. Irrigation uniformity indices are adapted for use in fertilizer application uniformity evaluation. Fertilizer application rate, given as a function of irrigation depth and fertilizer concentration, is identified as the appropriate variable to express fertilizer application uniformity indices. Pertinent mathematical properties of the uniformity indices along with their practical fertigation management implications are outlined. Carefully designed hypothetical fertigation scenarios were analyzed to examine the significance of the interactive effects, of the local spatial trends of depth and concentration data, on the test-plot scale uniformity of the resultant fertilizer application rate data. The results of the study show that the spatial overlap patterns between depth and concentration data sets are the main determinants of test-plot scale fertilizer application rate uniformity. The study also shows that often the uniformity levels of irrigation and fertilizer concentration data sets cannot be uniquely related to the uniformity of the resultant application rate data. However, some practically useful qualitative relationships between the uniformity of irrigation depth, solute concentration, and application rate data sets are defined. Application of the approach presented here in the evaluation and analysis of fertigation uniformity data sets, measured under sprinkler irrigated conditions, is highlighted.

Solid-set sprinklers irrigation of field boundaries: experiments and modeling

Numerous studies have analyzed the solid-set sprinkler irrigation system performance. However, the effect of field-boundaries irrigation has not been considered in the whole-field performance. The objectives of this study were (1) to characterize two different solutions to irrigate field boundaries (full-circle sprinkler equipped with a deflecting plate, DP, and partial-circle sprinklers, PC); (2) to calibrate and validate a ballistic model to adequately simulate these solutions; and (3) to analyze the two different designs (DP or PC) from a whole-field perspective. Two types of experiments were designed. The first was carried out with an isolated sprinkler under no windy conditions to estimate drop size distribution parameters. The second was performed in a solid-set sprinkler layout under windy conditions to calibrate and validate the ballistic model. The experimental design allows the comparison of both solutions under equal technical and meteorological conditions. Comparisons between designs (DP or PC) were established for a whole-field area in terms of irrigation performance and crop yield. From a technical point of view, PC sprinklers perform better than DP sprinklers. From an economical point of view, the shape and orientation of the plot and the legal requirements of the irrigation system design (minimum distance of the sprinkler line to the border) have an important effect on the optimal solution to irrigate field boundaries.

Sprinkler irrigation uniformity and crop water productivity of barley in arid region

An investigation has been organized To study the effect of the sprinkler irrigation system design on irrigation uniformity and its impact on barley crop yield and crop water productivity (CWP). The spring irrigation operating pressures (P) were 200 kPa (P1), 250 kPa (P2) and 300 kPa (P3). The sprinkler riser heights were 100 cm (H1), 125 cm (H2) and 150 cm (H3) from the ground. The results demonstrated that the maximum values of coefficient of uniformity (CU) and distribution uniformity (DU) (91.37 % and 0.85, respectively) were obtained at P3H3, while the minimum values (78.21 % and 0.71, respectively) were obtained at P1H1.Under P3H3 treatment, the highest values of 5.50 t ha-1 and 63.49 cm of grain yield (GY) and barely plant height (PH), respectively were recorded. The highest CWP value (0.75 kg m-3) was obtained when the P3H3 treatment was applied, while the lowest yield (0.36 kg m-3) was recorded under P1H1 treatment. According to the results of this experiment, under Sebha environmental conditions and similar regions, it is recommended to operate the solid set sprinkler irrigation system at P3H3 to obtain the highest CU and DU and consequently the highest GY, PH and CWP.

Development and validation of a modified model to simulate the sprinkler water distribution

Water distribution uniformity is important for the design of a sprinkler irrigation system. The movement of enormous water droplets after leaving the sprinkler nozzle significantly affect the water distribution of an individual sprinkler. Based on modified mathematical models of droplet dynamics and evaporation, a method for simulating droplet motion was proposed, and a corresponding software was developed as well. Using the given radial water distribution data of an individual sprinkler, the software can predict the water distribution of an individual sprinkler or a solid-set sprinkler irrigation system under different sprinkler spacing combinations and various environmental parameters. The corresponding combined application rate (P¯), coefficient of uniformity (CU) and evaporation loss rate of an irrigation system could be calculated. The model was validated by indoor and field experiments. The side length of the grid elements constituting the square region was recommended as 0.5m and the number of spray directions was 180 in the simulation. The results of model validation showed that the simulated radial water distribution of an individual sprinkler agreed well with the measured values, with a confidence coefficient of 0.899. The average relative errors in P¯ and CU between the measured and simulated values were 3.46% and 2.46%, respectively. The developed software package was capable of predicting the water distribution of sprinkler irrigation systems with relatively high accuracy under the conditions investigated.

Effect of Low Pressure on Irrigation Uniformity of Solid Set Sprinkler Irrigation System

The irrigation requires an efficient and effective method of water application to realize maximum return and conserve water resources. The low pressure sprinkler irrigation system is the most commonly used due to: its low energy cost, but the irrigation uniformity of this system is not constantly good because it is affecting by the design factors such as: nozzle type, nozzle diameter, operating pressure and spacing layout. But the most important factors are the operating pressure and nozzle diameter. In this study the effect of low pressure on the irrigation uniformity of the solid set sprinkler irrigation system was studied. Different low operating pressures (62, 82, 102 and122 kPa) were selected and different nozzle diameters (4, 5 and 7 mm) were used. The solid set layout was square (12 m between the sprinklers along the line and 12 m among the line). The catch-cans test was used to determine the uniformity coefficients such as: Christiansen’s coefficient of uniformity (CU), coefficient of variation (CV), distribution uniformity of low quarter (DUlq) and distribution uniformity of low half (DUlh). The distribution characteristics such as: throw radius and rotation speed were monitored. A comparison was made between the results obtained from different combination of operating pressures and nozzle diameters. The results of this study showed that, CU, DUlq and DUlh were increased when the pressure increased for all the nozzles. The greater values of CU, DUlq and DUlh were found with the combination of 7 mm nozzle diameter and 122 kPa. The coefficient of variation was increased when the pressure decreased for all the nozzles. The throw radius and rotation speed were increased gradually when the pressure increased. The throw radius was not significantly affected by the nozzle diameter while the rotation speed was more affected by the nozzle diameter.

Field-Scale Sprinkler Irrigation System Hydraulic Model. II: Hydraulic Simulation

AbstractThis paper describes a mathematical model for the hydraulic characterization of a field-scale solid set sprinkler irrigation system with a double-line lateral layout configuration. Formulation of the basic hydraulic equations along the mainline and laterals is based on manifold hydraulics. Lateral hydraulics remains the same as that described in a previously published paper, for systems with single-line laterals. A description of the mainline hydraulics of systems with a double-line lateral layout configuration, which requires the formulation and iterative solution of a system of nonlinear equations, is presented here. The hydraulic characterization functionality of the model, described in a previously published paper, serves as an interface for coupling the numerical solutions of the lateral and mainline hydraulic equations. In addition, this paper presents a description of the simulation functionality of the sprinkler hydraulic model and a related numerical algorithm, which is based on one-dimen...

PERFORMANCE EVALUATION OF SOLID-SET SPRINKLER IRRIGATION UNDER DIFFERENT PRESSURES AND NOZZLE DIAMETERS

Low irrigation efficiency and limited fresh water resources become serious issues worldwide particularly in arid and semi-arid regions. Rapidly deep percolation of water especially in light-textured soils needs efficient irrigation systems for water application. The overall irrigation efficiency can be increased through choosing the optimum operating conditions. This study investigated the effects of both operating pressure and nozzle diameter on the performance of the solid set sprinkler irrigation system. Three levels of operating pressure of (160, 180 and 200 kPa) and three different nozzle diameter of 3.0, 4.2, and 5.2 mm were used. The distribution efficiency of water was evaluated through the calculation of Christiansen’s uniformity coefficient (CU), distribution uniformity, application uniformity and precipitation rate. The results demonstrated that 180 kPa operating pressure produced the highest distribution uniformity, coefficient of uniformity and application uniformity.

Evaluation of uniformity coefficients for sprinkler irrigation systems under different field conditions in Kurdistan Province (Northwest of Iran)

In the past few decades, several coefficients of uniformity were developed to express the uniformity of water distribution for different sprinkler irrigation systems. Christiansen's uniformity coefficient seems to be the most popular uniformity coefficient used by researchers on the global scale. However, more coefficients have also been proposed by other researchers. Therefore, this study focused on evaluating different uniformity coefficients proposed and on investigating the effects of field conditions on the results obtained by means of those coefficients. In doing so, sprinkler uniformity tests were conducted by using rain-gauge in order to measure the uniformity coefficients of ten fields irrigated by solid set sprinkler irrigation systems in Dehgolan Plain located in the Kurdistan Province, northwest of Iran. All fields selected differed in prevailing conditions such as the wind speed, size and type of nozzle, raiser height, operating pressure and sprinklers spacing. The coefficient of uniformity for each field was computed using the equations proposed by Christiansen (1942), Hawaiian Cane Society Specialists Hart and Reynolds (1965), Wilcox and Swailes (1947), Karmeli (1978), Criddle et al. (1956), Benami and Hore (1964), and Beale (1966). Data analysis was performed using the general linear model procedure of Statistical Analysis System Software. The results indicated that should not the field effect be considered in the statistical model, significant differences (P &amp;lt; 0.05) would be observed between the aforesaid coefficients; however, by considering the field effect in the statistical model, no significant differences (P &amp;gt; 0.05) would be observed. The results of this study conclusively indicated that the application of various coefficients of uniformity depends on the field conditions and as any specific coefficient of uniformity is suitable only for specific field conditions.

A Simplified Method for Field Evaluation of Solid Set Sprinkler Irrigation Systems

Solid-set sprinkler irrigation has been widely used around the world because it can improve water application efficiency, increase crop production, and reduce environmental impact of irrigation. The uniformity of water distribution is a very important factor in the design and management of these sprinkler irrigation systems. In this article, a statistical method based on the coefficient of variation (CV) is evaluated using existing data to verify the rationale of this method. Two data sets of the water depths measured from different sprinkler systems were obtained. Eighteen randomly selected points from each data set were proved to be satisfactorily significant to evaluate the distribution of the intensity with 95% confidence limits compared with the results from the actual data points. A significant amount of labors and time can be saved with the application of this method when compared with the other traditional methods. This is a simple method that can provide irrigators, turf managers, and farmers a useful tool to evaluate the water distribution from their sprinkler irrigation systems.

Evaporation losses, efficiency and irrigation uniformity for center pivot and solid set sprinkler irrigation systems

أجریت دراسة حقلیة خلال عام 2007 لمقارنة فواقد التبخر من الرذاذ وکفاءة وتناسق الری بین نظامی الری بالرش المحوری والری بالرش الثابت. إذ تم تنفیذ التجربة فی موقعین من محافظة الانبار.بینت نتائج الدراسة إن متوسط فواقد الرذاذ خلال سنة الدراسة تحت ظروف نظام الری بالرش المحوری بلغت 9.38% من کمیة المیاه، بینما کانت 13.05 بالنسبة لنظام الری بالرش الثابت. کما أوضحت نتائج الدراسة أن قیمة کفاءة الری ومعامل التناسق لکلا موقعی الدراسة کانت 90.61 و 90.90 على التوالی بالنسبة لنظام الری بالرش المحوری. بینما کانت 86.95 و 80.70 بالنسبة لنظام الری بالرش الثابت.

Sprinkler droplet size distribution measured with an optical spectropluviometer

In solid set sprinkler irrigation systems, many factors have influence on water partitioning efficiency and uniformity. Drop size formation in the irrigation process is affected by some of these factors. Soil crustiness and damage to bare soil structure are problems associated with large drops. This study shows the results of measured drop size distributions in medium-sized sprinklers. An optical spectropluviometer (OSP) with infrared beam was used to measure drop size distributions. A variety of factors were checked: sprinkler type, nozzles, jet straightening vane and working pressure. The results showed that working pressure has the most influence on drop sizes; under low-pressure conditions, drops with a diameter of about 9 mm can be formed. The influence of the jet straightening vane and the types of nozzles and sprinklers has also been studied. A good similitude is obtained between the medium drop diameters measured and those simulated with the SIRIAS ballistic simulation model.

A case study for irrigation modernisation: II: Scenario analysis

Surface irrigation simulation models have seldom been used in engineering practise, and district modernisation is not an exception. Surface irrigation evaluations were performed in the Almudévar irrigation district to obtain the parameters required for surface irrigation modelling. The total district irrigated area was divided into 92 design units, for which a characteristic blocked-end border was defined. Simulation was used to establish the current irrigation performance in each design unit, and district performance contour maps were built. Irrigation performance was characterised using potential application efficiency, with an average of 54%, and irrigation time, averaging 6 h ha −1. Simulated potential application efficiency of the low quarter was similar to the seasonal irrigation performance index (an estimate of irrigation efficiency) presented in the companion paper. A set of seven modernisation scenarios was defined. Two strategies were identified to improve the potential application efficiency in the scenarios: increase the irrigation discharge into the current blocked-end borders and/or substitute the current system with a solid set sprinkler irrigation system. The performance of each scenario was estimated using irrigation models to determine efficiency, water conservation and irrigation time. The modernisation investment costs were estimated and compared to the performance of each scenario. The best results (potential application efficiency of 77%, reduced water allocation by 14.4 10 6 m 3 year −1) were obtained by a combination of blocked-end irrigation with a discharge of 200 l s −1 and sprinkler irrigation in the areas where surface irrigation efficiency could not attain 50%. The investment cost for this scenario was 3932 Euro ha −1. More expensive scenarios did not guarantee better performance.

Field Scale Transport of Bromide Under Variable Conditions Observed in a Furrow-irrigated Field

An experiment was conducted during the summer of 1991 to monitor field scale movement of bromide (Br-) under the variable conditions observed in a 0.81-ha furrow-irrigated fallow field. Twenty-one evenly spaced sampling stations were established, each consisting of a soil solution sampler at 0.3-m depth, and a neutron probe access tube to a depth of 2.1 m. A narrow pulse of Br- tracer was applied by injection through a solid-set sprinkler irrigation system and was subsequently transported downwards by 26 mm of sprinkler irrigation. Three furrow irrigation events were conducted at three-week intervals during the 63-day study period. Soil samples were taken at each station in 0.15-m increments to a depth of 2.4 m prior to each irrigation and at the end of the study period. The three furrow-irrigation events moved the solute front to 0.23-, 0.38-, and 1.13-m depth, respectively. Three piston flow models based on Darcy flow, field capacity, and the Transfer Function model (TFM) were used to predict the movement of the solute. The Darcy flow model under-estimated solute movement by 18% to 43% after each irrigation event. The TFM predicted the movement of solute with reasonable accuracy after the first irrigation but overestimated solute movement for subsequent irrigations. The latter was attributed to the need to calibrate the TFM at deeper depths. The field capacity model was more consistent with observed irrigations, and predicted the movement of solute with reasonable accuracy for the first and second irrigation. However, the field capacity model underestimated the final Br- position. It was hypothesized that preferential flow occurred during the third irrigation, since the infiltration rates increased during this irrigation and the final measured position of Br- was significantly greater than predicted by the piston flow models.

A Sprinkler Water Droplet Evaporation and Plant Canopy Model: II. Model Application

A model that combines water droplet evaporation and three-dimensional droplet trajectory equations with a comprehensive plant environment model is validated under field conditions for a solid-set sprinkler irrigation system by comparing field measurements of air temperature and vapor pressure with predictions for a mature corn canopy. Irrigation water temperature was significant in determining evaporation loss of droplets during flight. Although direct evaporation loss of water droplets was minimal (< 1%), a total amount of energy equivalent to 24% of the net radiation during irrigation was transferred from the plant-environment to the water droplets as they were warmed during flight and after they impacted the canopy and soil. Substantial errors in computing the energy balance of the plant-environment can be made by assuming that all droplets are at the wet bulb temperature when they reach the canopy. For the case study in this article, about 8% of the applied water was evaporated during irrigation, but only 3% of the water applied by an overhead sprinkler system was truly lost to the plant during the day of irrigation because transpiration and soil evaporation would have occurred even without irrigation. This indicates that irrigation efficiencies can be higher than previously expected with large solid-set irrigation systems.