Experimental and numerical investigation of laboratory scale sheetpipe-typed automatic subsurface irrigation

Sheet pipe is a type of perforated pipe used for drainage designed initially for drainage but has the potential for sub-surface irrigation. The objectives of this study were to experiment and observe the performance of the sub-surface irrigation control system with sheet pipe. This investigation covered the observation of water table control and its effect on soil moisture. The detailed process of water flow during the setting of the water table was numerically modeled in 2 dimensions to observe the distribution of soil moisture, soil pressure, and flux. The results showed that the system successfully controlled the water table at the desired level in the experiment. The developed two-dimensional numerical simulation showed the distribution of soil moisture in the model center as a response to the water table increase, represented by the variable head. The soil wetting advances toward soil surface driven by the water table, which was increased gradually and reached saturation at the height of water table setpoint.

Discharge Characterization and Variability Determination along Shorter Sections of Soaker Hose Pipe for Soil Column Experiment

Unlike other micro-irrigation facilities like a drip, trickle, and sprinklers that emits water at regularly spaced intervals with predefined discharges, porous rubber pipes (soaker hose) has openings of variable sizes that become unevenly spaced with uneven distribution. The latter makes discharge to be variant along its lateral. Shorter sections are used under laboratory column experiments of soil wetting pattern studies and for this reason, laboratory experiments were conducted to evaluate the extent of emission rates variability on short sections of commercial Irrigation Soaker Hose, 16 mm diameter. Three sections of 10 cm length pipes were randomly selected from 15 no's cuts from different parts of the twenty meters length pipe bundle and used to investigate the extent of variability on emission rates characteristics under six different operating pressures. The result was achieved by collecting and measuring water emitted through the pipe sections at pre-determined pressures. The various discharges, coefficient of variation, and pressure-discharge curves of the section of the pipe then determined from the data. The result shows somewhat similar trends on the increase for water collected with an increase in pressures; however, when statistically compared, the discharges among the pipe sections vary. The values of Coefficient of Variation (CV) are less than 10 % as the values CV range from 0.92 % to 5.82 %, which is within a good category, according to ASAE Standard EP405.1 of 0-10%. The findings indicate that, despite variations among the investigated sections, it can use any part as a representative unit in the soil column experiments with reasonable accuracy.

Development and Validation of a Model for Soil Wetting Geometry Under Moistube Irrigation

We developed an empirical soil wetting geometry model for silty clay loam and coarse sand soils under a semi-permeable porous wall line source Moistube Irrigation (MTI) lateral irrigation. The model was developed to simulate vertical and lateral soil water movement using the Buckingham pi (π) theorem. This study was premised on a hypothesis that soil hydraulic properties influence soil water movement under MTI. Two independent, but similar experiments, were conducted to calibrate and validate the model using MTI lateral placed at a depth of 0.2 m below the soil surface in a soil bin with a continuous water supply (150 kPa). Soil water content was measured every 5 minutes for 100 h using MPS-2 sensors. Model calibration showed that soil texture influenced water movement (\(p\) < 0.05) and showed a good fit for wetted widths and depths for both soils ( \(nRMSE\) = 0.5% − 10%; \(NSE \ge\) 0.50; and d-index \(\ge\) 0.50. The percentage bias \(\left(PBIAS\right)\) statistic revealed that the models’ under-estimated wetted depth after 24 h by 21.9% and 3.9% for silty clay loam and sandy soil respectively. Sensitivity analysis revealed an agreeable models’ performance values. This implies the applicability of the model for estimating wetted distances for an MTI lateral placed at 0.2 m. However, further experimentation under varying scenarios for which MTI would be used, including field conditions, is needed to further validate the model and establish robustness. MTI wetting geometry informs placement depth for optimal irrigation water usage.

Numerical Simulation of Water Distribution with Uptake Root in Drip Irrigation using Different Soil Hydraulic Models

Surface drip irrigation is one of the most conservative irrigation techniques that help control providing water directly on the soil through the emitters. It can supply fertilizer and providing water directly to plant roots by drippers. One of the essential needs for trickle irrigation nowadays is to obtain more knowledge about the moisture pattern under the trickling source for various types of soil with various discharge levels with trickle irrigation. Simulation numerical using HYDRUS-2D software, version 2.04 was used to estimate an equation for the wetted area from a single surface drip irrigation in unsaturated soil is taking into account water uptake by roots. In this paper, using two soil types were used, namely sandy loam and clay loam, with three types of plants; (corn, tomato, and sweet sorghum). The soil wetting pattern was analyzed each half an hour for three hours of irrigation time and three initial soil moisture content. Equations for wetted radius and wetted depth were predicted and evaluated by utilizing the statistical parameters for the different hydraulic soil models (Model Efficiency (EF) and Root Mean Squares Error (RMSE)). The values RMSE does not exceed 0.40 cm, and EF is greater than 0.96 for all types of soil. These values were between the values obtained from program HYDRUS-2D and the values obtained from formulas. This shows that evolved formula can be utilized to describe the soil wetting pattern from the surface drip irrigation system. The relative error for the different hydraulic soil models was calculated and compared with Brooks and Corey's model, 1964. There was good agreement compared with different models. RMSE was 0.23 cm, while the relative error -1% and 1 for EF for wetted radius.

Numerical investigation of wetting front migration and soil water distribution under vertical line source irrigation with different influencing factors

Vertical line source irrigation (VLSI) is an underground irrigation method suitable for deep-rooted plants. Understanding the characteristics of the soil wetting body of the VLSI was the key to designing this irrigation system. On the basis of experimental verification of the reliability of the HYDRUS simulation results of VLSI under the conditions of soil texture (ST), initial water content (θi), line source buried depth (B), line source diameter (D) and line source length (L), numerical studies of the migration law of the wetting front of VLSI and the distribution characteristics of soil moisture were performed. The wetting front migration (WFM) was mainly influenced by ST, θi, D and L (P &lt; 0.05), while B had little effect on WFM (P &gt; 0.05). The shape of the soil wetting body changed little under different influencing factors. The water content contour was approximately ‘ellipsoidal’ around the line source. The soil moisture near the line source was close to the saturated moisture content. The moisture content around the line source gradually decreased outward, and the contour lines gradually became dense. According to the simulation results, a prediction model of multiple factors influencing the migration process of the VLSI wetting front was established. The predicted value was in good agreement with the measured value. The results of this research could provide a theoretical basis for further optimizing the combination of VLSI and irrigation elements.

Establishment and verification of the prediction model of soil wetting pattern size in vertical moistube irrigation

To solve the difficulty of observing the soil wetting pattern of vertical moistube irrigation, the HYDRUS-2D software is used to simulate wetting pattern data under different conditions. Based on the analysis of Origin 9.0 and summarizing the law of simulation data, an empirical model for predicting wetting pattern size is constructed, with the reliability of the model verified by experimental data. The results show that the power function is used to fit the relationship between the size of wetting pattern and irrigation time. The power function exponent has small changes in three directions (vertical upward, horizontal, and vertical downward) of the moistube. Further analysis shows that the power function coefficient is in accordance with the power function relationship with soil-saturated hydraulic conductivity, the steady permeability of the moistube, and the difference between soil-saturated moisture content and initial moisture content. The average absolute error of statistical indicators of the built model is between 0.30 and 1.42 cm, the root mean square error is between 0.42 and 1.65 cm, and the Nash–Sutcliffe efficiency coefficient is not less than 0.93. The model has a good prediction effect and can provide a scientific basis for the design, operation, and management of the moistube irrigation engineering.