Impacts of spatial variability of basins microtopography on irrigation performance

Land microtopography unevenness is a key variable affecting basin irrigation performances. Using stochastic modeling, a number of sets of spatially variable surface elevations were generated, and a two-dimensional basin irrigation model was used to simulate irrigation for the generated sets. Strip, narrow and wide basins, as well as graded and zero-levelled basins were analyzed. Results show that spatial variability of basin microtopography influences the infiltrated depth when the advance is completed (Z _adv) and the irrigation uniformity (DU_lq). When the degree of unevenness increases, the Z _adv value and its range of variation also increase, thus indicating that overirrigation increases with unevenness, mainly when zero leveling is adopted, inflow rates are small, and basin length is larger. Differently, DU_lq is relatively small and insensitive to unevenness in case of graded basins, but is much larger and sensitive in case of zero leveling. This indicates that when water saving is aimed, it is preferable to adopt graded basins and shorter cut-off times, while it is better to adopt zero leveling and high inflow rates when high DU_lq is pretended.     

Characterizing microtopographical effects on level-basin irrigation performance

Microtopography has long been recognized as one of the key variables in level-basin irrigation performance, although little effort has been devoted to establish its relevance. In this work, experimental data are used to quantify the influence of microtopography on irrigation performance. An irrigation evaluation was performed on a small level-basin (256 m²) LASER levelled to zero slope. Irrigation depth was gravimetrically measured and estimated at the 49 nodes of a regular network. Data from the irrigation evaluation and a two-dimensional flat-bed model were used to estimate irrigation depth. Irrigation times, soil surface elevation and distance to the inlet were estimated at the same nodes, and a correlation matrix was computed. Results showed that soil surface elevation was highly and significantly correlated with the times of advance (0.725⁷¹), recession ( −0.815⁷¹) and opportunity ( −0.852⁷¹), and with the measured irrigation depth ( −0.583⁷¹). Distribution uniformity using soil water measurements was 71.0%. Estimates from the irrigation evaluation and the two-dimensional model were 85.3% and 94.9%, respectively. The irrigation evaluation procedure could explain 30⁷¹% of the measured variability in irrigation depth. A large part of the unexplained variance in measured irrigation depth seems to be due to the spatial variation of infiltration properties. Predictions by the two-dimensional model were not significantly related to the measured values. A simple method was devised to estimate microtopography-adjusted irrigation performance from the results of a flat bed model and the standard deviation of elevation. Microtopography can have an important effect on level-basin irrigation performance. Models not considering this variable may incur large errors when simulating irrigation performance.     

A spreadsheet model to evaluate sloping furrow irrigation accounting for infiltration variability

A spreadsheet model was developed to evaluate the performance of furrow irrigation that accounts for soil variability and requires few field measurements. The model adjusts an advance trajectory to three (advance distance, advance time) points and, similarly, it adjusts a recession trajectory to three (recession distance, recession time) points. The head of the furrow (distance = 0) is one of the points used to adjust both trajectories. It then calculates the parameters of the infiltration equation using the two-point method (based on the volume balance equation with assumed surface shape parameters). The model gives the option to enter an estimate of the soil infiltration variability in order to account for this variation when calculating irrigation performance indicators. The combination of variance technique was used for this purpose. A set of irrigation performance indicators (distribution uniformity, application efficiency, tail water ratio, deep percolation ratio and deficit coefficient) is calculated, assuming that the infiltrated water follows a normal frequency distribution. To illustrate the evaluation method, it was applied to three irrigation events conducted on a sunflower field, with 234 m long furrows spaced 0.75 m apart. The evaluations were performed in two 3-furrow sets. The application efficiency was satisfactory in the first irrigation, but low in the other two. Uniformity was high in all three irrigations. The performance indicator that was most affected by soil variability was distribution uniformity. Considering soil spatial variability was important for more realistic determination of the infiltrated water distribution, and therefore of the deep percolation, but it had less importance for the determination of the application efficiency, due to the relevance of runoff in our field application.     

Determination of infiltration rate from border irrigation advance and recession trajectories

A volume-balance technique utilizing irrigation advance and recession functions, numerical integration, and an optimization procedure was developed to determine infiltration parameters. The procedure is simple yet rational and accounts for spatial variability of soil characteristics. The required data are flow rate, the coefficients and exponents of the advance and recession functions, and inflow shut-off time. In a field experiment on a clay loam soil (typical of southern Alberta) at the Lethbridge Research Centre, infiltration rates estimated by this technique were similar and in close agreement with those measured with a ring infiltrometer. Except for two border strips, there were no significant mean differences between simulated (I_s) and measured (I_m) infiltration rates. In the two non-conforming border strips, field measured infiltration rates were higher than those simulated with the volume balance approach, most likely due mainly to spatial variability of soil characteristics and partly to lateral flow which occasionally occurs when measuring infiltration with a ring infiltrometer.     

Evaluation of time domain reflectometry (TDR) for estimating furrow infiltration

TDR was used to estimate furrow infiltration, which is a key component in furrow irrigation system design and management. Furrow irrigation experiments were conducted on bare and cropped fields consisting of three 40 m long parabolic shaped furrows spaced at 0.8 m on a slope of 0.5%. The centre furrow was taken as the study furrow and the other two provided a buffer to the centre furrow. Altogether, 22 irrigations were conducted during 2004 and 2005 with inflow rates ranging from 0.1 to 0.7 l s⁻¹. TDR probes were installed vertically around the centre furrow at four locations 0.5 (S₁), 13 (S₂), 26 (S₃) and 39.5 m (S₄) from the inlet end. The S₁ and S₃ locations had four TDR probes installed at 0.15, 0.30, 0.45 and 0.60 m depths whereas the S₂ and S₄ locations had two probes each at 0.15 and 0.30 m depths. Soil moisture data collected at 5-min intervals were used to determine the average soil moisture content of the field. The change in moisture content was used to estimate the furrow infiltration which was compared with that measured using an inflow–outflow (IO) method. The performance of the TDR method was studied by calculating the absolute prediction error (APE), root mean square error (RMSE) and index of agreement (I _a). It was found that the TDR-method estimated furrow infiltration well for higher inflow rates and during the initial stages of irrigation. APE decreased and I _a increased with increase in flow rate for both bare and cropped conditions. The APE and RMSE were found to be larger for a cropped field than the bare field when irrigated at the same inflow rate. The accuracy of the TDR-method for estimating total infiltration was improved by using the average field moisture content of 30 or 45 min after the recession phase ceased. These results indicate that TDR can be used to estimate in situ infiltration under furrow irrigation.     

Evaluation of surface irrigation as a function of water infiltration in cultivated soils in the Nile Delta

As sources of irrigation water are decreasing, efficient use of surface irrigation is essential. The purpose of this study is to determine if partially-wetted furrow irrigation has more efficient water storage and infiltration than traditional border irrigation in an alluvial clay soil under cultivated grape production. The two irrigation components considered were wet (WT) and dry (DT) treatments, at which water was applied when available soil water reached 65 % and 50 %, and the traditional border irrigation control. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. Coefficient of variation (CV) was 5.2 and 9.5 % for WT and DT under furrow irrigation system comparing with 7.8 % in border, respectively. Water was deeply percolated as 11.9 and 19.2 % for wet and dry furrow treatments respectively, compared with 12.8 % for control, with no deficit in the irrigated area. Partially-wetted furrow irrigation had greater water-efficiency and grape yield than dry furrow and traditional border irrigation, where application efficiency achieved as 88.1 % for wet furrow irrigation that achieved high grape fruit yield (30.71 Mg /ha). The infiltration (cumulative depth, Z and rate, I) was functioned to opportunity time (t ₀ ) in minute for WT and DT treatments as: Z _WT ?=?0.528?t ₀ ^0.6, Z _DT ?=?1.2?t ₀ ^0.501, I _WT ?=?19?t ₀ ^?0.4, I _DT ?=?36?t ₀ ^?0.498. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. The irrigation parameters and coefficients, and soil water distribution have been also evaluated.     

Two-dimensional zero-inertia model of surface water flow for basin irrigation based on the standard scalar parabolic type

The two-dimensional zero-inertia equations for basin irrigation were formulated as a standard scalar diffusion equation subject to Neumann boundary conditions. The formulation can handle anisotropic variations in hydraulic resistance. A numerical solution was developed using finite-volume method on unstructured triangular cells. The simulation performance of the constructed model was validated based on typical experimental data. The complete hydrodynamic model of basin irrigation was selected as the comparative model. The validated results show that the constructed model can successfully simulate the basin surface water flow when the basin surface microtopography condition is relatively smooth. Similar results were found in terms of both the water quantity conservation and convergence rate. Moreover, the computational efficiency of the constructed zero-inertia model is approximately 17 times of the complete hydrodynamic model of basin irrigation. Therefore, the constructed zero-inertia model has good simulation performance.     

Zero-inertia model for surge flow furrow irrigation

Summary A surge flow furrow irrigation model was developed based on the zero-inertia concept originally developed by Strelkoff and Kastapodes, (1977) for border irrigation and later modified for continuous furrow irrigation by Elliot et al. (1982). The model simulates all phases of continuous and surge flow irrigation including simultaneous advance and recession and can also be applied to basin and border irrigation with various field slopes. The surge model was verified for a wide range of actual field conditions and management alternatives. A sensitivity analysis was performed for the size of time step and the physical input parameters.     

微地形及沟断面形状变异性对沟灌性能影响的试验研究

针对沟灌,研究了沟底起伏状况和沟横断面形状的空间变异性对灌水质量的影响。通过分析在河北吴桥开展的棉花沟灌试验数据,描述了灌水沟断面形状和沟底高程二因素的空间分布特征。采用田面平整精度Sd值作为评价沟底高程变化程度的指标,确定其对灌水均匀度和灌水效率的影响;采用断面形状参数p2描述灌水沟断面形状,以p2的标准差反映其空间变异性对地表水流运动和灌水质量的影响。结果表明,灌水均匀度和灌水效率均随沟底高程标准差的增大而减小;水流推进速度随断面形状参数p2标准差的增大而降低,灌水均匀度和灌水效率随p2标准差的增大而减小。因此,微地形和灌水沟断面空间变异性,对灌水均匀度和灌水效率均有显著的影响。     

Simulation of furrow irrigation practices (SOFIP): a field-scale modelling of water management and crop yield for furrow irrigation

Because of the spatial and temporal variabilities of the advance infiltration process, furrow irrigation investigations should not be limited to a single furrow irrigation event when using a modelling approach. The paper deals with the development and application of simulation of furrow irrigation practices (SOFIP), a model used to analyse furrow irrigation practices that take into account spatial and temporal variabilities of the advance infiltration process. SOFIP can be used to compare alternative furrow irrigation management strategies and find options that mitigate local deep-percolation risks while ensuring a crop yield level that is acceptable to the farmer. The model is comprised of three distinct modelling elements. The first element is RAIEOPT, a hydraulic model that predicts the advance infiltration process. Infiltration prediction in RAIEOPT depends on a soil moisture deficit parameter. PILOTE, a crop model, which is designed to simulate soil water balance and predict yield values, updates the soil moisture parameter. This parameter is an input of a parameter generator (PG), the third model component, which in turn provides RAIEOPT with the data required to simulate irrigation at the scale of an N-furrow set. The study of sources of variability and their impact on irrigation advance, based on field observations, allowed us to build a robust PG. Model applications show that irrigation practices must account for inter-furrow advance variability when optimising furrow irrigation systems. The impact of advance variability on deep percolation and crop yield losses depends on both climatic conditions and irrigation practices.     

Comparison and selection of furrow irrigation models

The capability of hydrodynamic, zero-inertia, kinematic-wave and volume-balance models to predict advance and recession phases in furrow irrigation were compared against two sets of field data, providing a wide range of soil conditions and field slopes. The input parameters required for each model were studied, and a simple sensitivity analysis was performed for field slope, furrow geometry, roughness coefficient, infiltration constants, time step, and discharge. The accuracy of the models' predictions depends on the precision of the measurements and the estimation of the input parameters. Excellent prediction of the advance and recession phases were obtained with hydrodynamic, zero-inertia and kinematic-wave models. Those models therefore are preferred in design and management in furrow irrigation.     

Elevation and infiltration in a level basin. I. Characterizing variability

Spatial characterization of soil physical properties could improve the estimation of surface irrigation performance. The aim of this research was to characterize the spatial and time variability of a set of irrigation-related soil properties. The small-scale experimental level-basin (729 m²) was located on an alluvial loam soil. A corn crop was established in the basin and irrigated five times during the season. A detailed survey of the soil properties (generally using a 3 × 3 m network) was performed. Classic statistical and geostatistical tools were used to characterize the variables and their interactions. Semivariograms were validated for the studied variables, except for the clay fraction, the saturated hydraulic conductivity and the infiltration parameters. The resulting geostatistical range was often in the interval of 6–10 m. For the three surveys of soil surface elevation the range was smaller, about 4 m. No correlation was found between saturated hydraulic conductivity and the other soil physical properties. Soil surface elevation showed a high correlation between surveys. After the first irrigation, the standard deviation of elevation increased from an initial 9.6 mm to 20.8 mm. The soil physical parameters were used to map the soil water management allowable depletion. In a companion paper these results are used to explain the spatial variability of corn yield and soil water recharge due to irrigation. Received: 24 February 1998     

Comparison of spatial interpolation methods for yield response factor of winter wheat and its spatial distribution in Haihe basin of north China

Yield response factor (K _y) is an important basis for implementing efficient irrigation and optimal water allocation. Because K _y varies in different sites, understanding its spatial distribution plays an important role in optimization irrigation in Haihe basin. After determining the K _y and ET₀ of winter wheat, an exponentially increasing function was found between the two parameters. Then, spherical and exponential semivariograms were chosen as proper theoretical models for ET₀ and K _y, respectively, with R ² of more than 0.970. By comparing six interpolation methods as well as two procedures, i.e. ‘calculate first, interpolate later’ (CI) and ‘interpolate first, calculate later’ (IC), IC-RK (residual kriging) was considered as an optimal method in interpolating K _y. Mapping of K _y for winter wheat indicated an increasing trend from the western and northern mountainous region to the eastern plain region in the basin, with the K _y of 0.783–1.668 for the dry growing season, 0.760–1.460 for the average growing season and 0.749–1.293 for the wet growing season. Moreover, the K _y values were more than 1.0 over the most of this basin, indicating that yield loss was more important than evapotranspiration deficit, and there were greater effect of water stress on the yield of winter wheat.     

A mathematical model for border irrigation II. Vertical and horizontal recession phases

Summary This paper, second in a series of three, develops a mathematical model, using the volume balance approach, to simulate vertical and horizontal recession of border irrigation. An equation is proposed for computing Manning's roughness factor N in both laminar and transitional flow regimes in recession phases. The model has four parameters which can be determined experimentally. Experimental data from ten vegetated as well as nonvegetated borders were used to verify the model. Average difference (AD) between calculated and observed vertical recession times was less than 4.4 min, and between calculated and observed horizontal recession times less than 4.6 min for the ten experimental data sets. Average relative error (ARE) in computed horizontal recession was less than 13% for these data sets. The model was found to be especially accurate for Reynold's number between 1,800 and 2,500.     

Effects of water infiltration and storage in cultivated soil on surface irrigation

Surface irrigation analysis and design require the knowledge of the variation of the cumulative infiltration water Z (L) (per unit area) into the soil as a function of the infiltration time t (T). The purpose of this study is to evaluate water infiltration and storage under surface irrigation in an alluvial clay soil cultivated with grape yield, and to determine if partially wetted furrow irrigation has more efficient water storage and infiltration than traditional border irrigation. The two irrigation components considered were wet (WT) and dry (DT) treatments, at which water applied when available soil water reached 65% and 50%, and the traditional border irrigation control. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. The infiltration (cumulative depth, Z and rate, I) was functioned to opportunity time (t_o) in minute for WT and DT treatments as: Z_WT = 0.528 t_o^0.6, Z_DT = 1.2 t_o^0.501, I_WT = 19 t_o^−0.4, and I_DT = 36 t_o^−0.498. The irrigation efficiency and soil water distribution have been evaluated using linear distribution and relative schedule depth. Coefficient of variation (CV) was 5.2 and 9.5% for WT and DT under furrow irrigation system comparing with 7.8% in border, respectively. Water was deeply percolated as 11.88 and 19.2% for wet and dry furrow treatments, respectively, compared with 12.8% for control, with no deficit in the irrigated area. Partially wetted furrow irrigation had greater water-efficiency and grape yield than both dry furrow and traditional border irrigations, where application efficiency achieved as 88.1% for wet furrow irrigation that achieved high grape fruit yield (30.71 Mg/ha) and water use efficiency 11.9 kg/m³.     

Methods for estimating irrigation needs of spring wheat in the middle Heihe basin,China

Understanding reference crop evapotranspiration (ET₀) is essential in planning the most effective use of water resources in the arid northwest China. The objective of the present work in the middle Heihe River basin were: (1) to determine the best model for calculating the areal distribution of reference crop evapotranspiration in this region, and (2) to estimate the spatial distribution of the irrigation requirements of spring wheat. Note that eight commonly used formulates were tested and that FAO-Penman was the best.The irrigation amount of spring wheat in 2000 was estimated by three steps. First, DEM-based and GIS-assisted methods were employed to estimate the spatial distribution of reference crop evapotranspiration (ET₀) according to FAO-Penman model. Then, spring wheat evapotranspiration (ET) was calculated by ET₀ and crop-coefficient (K_c). Finally, the maximum irrigation amount of spring wheat was estimated with the spring wheat evapotranspiration and precipitation in the different growing stage. The maximum irrigation has temporal–spatial variation. Temporally the irrigation amount appears the largest in June when it is the peak period of spring wheat development. The irrigation amount is the smallest in July because spring wheat was in late-season stage. In April, spring wheat was in seedling stage during which the water demand is also small. Spatially the irrigation amount increases from southeast to northwest.     

Temporal and spatial variations of evapotranspiration for spring wheat in the Shiyang river basin in northwest China

The methods for estimating temporal and spatial variation of crop evapotranspiration are useful tools for irrigation scheduling and regional water allocation. The purpose of this study was to develop a method for mapping spatial distribution of crop evapotranspiration and analyze the temporal and spatial variation of spring wheat evapotranspiration in the Shiyang river basin in Northwest China in the last 50 years. DEM-based methods were employed to estimate the spatial distribution of spring wheat evapotranspiration (ET_c). Reference crop evapotranspiration (ET₀) was calculated with the Penman–Monteith equation using meteorological data measured from eight stations in the basin. Crop coefficient (K_c) was determined from measured evapotranspiration in spring wheat season in the region. The results showed that ET_c gradually increased in the upper reaches of the basin in the last 50 years, while the middle reaches showed a significant decreasing trend, and in other regions, no significant trend was found. These changes can be attributed to expansion of irrigation areas and climate change. The multiple regression analysis between ET_c and altitude, latitude, and aspect were carried out for eight weather stations and the relationships were used to map ET_c for the basin. The spatial variations of ET_c were analyzed for three typical growing seasons based their precipitation. Results showed that long-term average ET_c over cultivated land was increasing from 270 mm in southwest mountainous area to 591 mm in northeast oasis of the basin, and the relative error between the estimated ET_c in spring wheat growing season by reference evapotranspiration (ET₀) and crop coefficient (K_c), and the interpolated ET_c was within 11.1%.     

The effects of different irrigation levels applied in golf courses on some quality characteristics of turfgrass

The purpose of this research was to examine the effects of different irrigation levels on evapotranspiration (ET) and quality characteristics of golf-course turfgrasses grown under Mediterranean climatic conditions and to determine the most economical irrigation level which would provide an acceptable turfgrass quality level. Four different irrigation treatments were examined: 100% (S₁), 88% (S₂), 75% (S₃), and 50% (S₄) of the evaporation measured in the Class A Pan. Treatment S₂ represented the existing irrigation level practiced by golf course management. The best color quality during the experimental period was obtained from the S₃ irrigation treatment, followed by S₂. Results regarding the ground cover percentage and root weights in the S₂ and S₃ treatments were better than S₁ and S₄. It was concluded that Class A Pan could be used to schedule turfgrass irrigation and 75% of evaporation from Class A Pan would be enough for irrigation. Additionally, it was found that 15% of irrigation water could be conserved compared with the current irrigation schedule (S₂), practiced by the owner.     

Determination of spatial water requirements at county and regional levels using crop models and GIS: An example for the State of Parana,Brazil

Due to the competitive use of available water resources, it has become important to define appropriate strategies for planning and management of irrigated farmland. To achieve effective planning, accurate information is needed for crop water use requirements, irrigation withdrawals, runoff and nitrate leaching as a function of crop, soil type and weather conditions at a regional level. Interfacing crop models with a geographic information system (GIS) extends the capabilities of the crop models to a regional level. The objective of this study was to determine the irrigation requirements, annual runoff and annual nitrate leaching for the most important crops of the Tibagi river basin in the State of Parana, Brazil. The computer tool selected for this study was the Decision Support System for Agrotechnology Transfer (DSSAT) version 3.5 (98.0) and its associated crop modeling and spatial application system AEGIS/WIN. It was assumed that farms within the same county use similar management practices. To achieve representative estimates of irrigation requirements, the weather data from stations located within each county or the nearest weather station were used. A weighting factor based on the proportion of soil type and crop acreage was applied to determine total annual irrigation withdrawals, annual runoff and nitrate leaching for each county in the river basin. The model predicted outputs, including yield, irrigation requirements, runoff and nitrate leached for different soil types in each county, were analyzed, using spatial analysis methods. This allowed for the display of thematic maps for irrigation requirements, annual runoff and nitrate leaching, and to relate this information with irrigation management and planning. The maximum annual irrigation withdrawal, runoff and nitrate leaching were 22,969 m³ per year, 31,152 m³ per year and 1488 t N per year in the Tibagi river basin. This study showed that crop simulation models linked to GIS can be an effective planning tool to help determine irrigation requirements for river basins and large watersheds.