Optimization of the border size on the irrigation district scale – Example of the Hetao irrigation district

Highlights

• The spatial distributions of soil physical parameters were analyzed of the Hetao irrigation district (HID).

• Proposed a method of estimating the infiltration parameters on the district scale.

• Measure 0–20 and 20–40 cm depths of soil physical parameters can satisfy the needs.

• Two types of optimal border layouts are proposed in the HID.

Abstract

To improve the performance of border irrigation, this study analyzed the spatial variability characteristics of the soil particle content and bulk density, based on soil physical parameters measured at 86 sampling points in the Hetao irrigation district (HID). The soil hydraulic parameters were determined using the RETC, and HYDRUS-1D was then adopted to estimate infiltration parameters of the Kostiakov equation at different locations. The optimal layout patterns of border size were proposed under the consideration of various combinations of different typical soil textures and field slopes by WinSRFR. The results indicated that the spatial distributions of clay and silt particle contents were generally high in the middle and low at both sides of the HID, while the sand was the opposite. The results proved that the soil physical parameters are only to be measured at depths of 0–20 and 20–40 cm to meet the needs of infiltration parameter estimation which can significantly reduce the workload of soil sample collection. Moreover, two types of optimal border layouts of different combinations of the soil textures (silt loam and silt clay loam) and field slopes (no more than 1‰, 1–3‰, and 3–5‰) were proposed, which can guarantee the application efficiency and distribution uniformity no less than 85%, and be the guidance for practical field irrigation in the HID.

Introduction

Border irrigation, a method of crop irrigation, is widely used because of its low cost and energy requirement. However, border irrigation systems are often inefficient due to over-irrigation and poor application uniformity (Gillies and Smith, 2015, Morris et al., 2015, Chari et al., 2019). Advanced simulation models of surface irrigation have been proven to be effective for evaluating system design and management and for improving irrigation performance. Infiltration parameters are essential input parameters for surface irrigation simulation models (Bautista et al., 2009, Salahou et al., 2018, Smith et al., 2018). Therefore, obtaining realistic estimates for infiltration parameters is vital.

Soil infiltration parameters are usually determined by direct or indirect methods. The direct method often uses single-ring or double-ring experimental data to determine the infiltration parameters (Gillies, 2008, Duan et al., 2011), and the indirect method (such as the one-point or two-point method) applies data regarding the water movement of surface irrigation to invert the infiltration parameters (Elliott and Walker, 1982, Valiantzas et al., 2001). However, both direct and indirect methods are very time consuming. Moreover, those methods are difficult to use for the estimation of infiltration parameters at the scale of an irrigation district. Due to the large area of an irrigation district, soil physical parameters (i.e. soil texture, bulk density, soil water content, etc.) may have significant variations. These factors then may lead to variability of infiltration. How to determine the infiltration parameters of an irrigation district is a crucial problem. Wosten and van Genuchten (1988) argued that acquiring infiltration parameters for an irrigation district is difficult or unnecessary; however, these parameters can be estimated by some simple methods. Because soil properties determine the infiltration capacity, the pedotransfer function (PTF) can be established. The PTF relates the estimated infiltration parameters to easily measured soil properties (Botula et al., 2012, Nguyen et al., 2015, Nie et al., 2017, Liao et al., 2020). RETC software, proposed by the USDA-Agricultural Research Service, is a software package that estimates the soil hydraulic parameters on the basis of easily measured soil physical parameters (e.g., soil particle content and bulk density). Many studies have proven that RETC software estimates of soil hydraulic parameters are reliable (Wei et al., 2004, Zhang et al., 2013). For parameters such as saturated water conductivity, the maximum relative error between the estimated and measured values is approximately 30%; however, the soil-water diffusion error is relatively small in low-suction sections, which are required for the design of field irrigation systems (Wei et al., 2004). Therefore, estimating soil hydraulic parameters by using RETC software is of practical value. With the estimated soil hydraulic parameters input into the HYDRUS software (Simunek et al., 2016), the infiltration process under different soil initial conditions can be simulated, and the corresponding infiltration parameters obtained. HYDRUS software is one of the most user-friendly models that can be used in the MS Windows environment. It is a software package for simulating water, heat, and solute movement in a variably-saturated media, and the reliability of the simulation results are proven by many studies (Kandelous and Simunek, 2010, Honari et al., 2017, Tu et al., 2021, Er-Raki et al., 2021). Therefore, RETC and HYDRUS softwares can provide rapid and accurate estimates of infiltration parameters for an irrigation district.

Numerous factors can affect the performance of border irrigation, including natural factors (i.e., soil texture and infiltration characteristics) and irrigation technology elements (e.g., border size, discharge, and cutoff time). Natural factors are not easy to change. Therefore, researchers seek to improve the performance of border irrigation by optimizing the combination of irrigation technology elements. Playan et al. (1996) showed that the performance of border irrigation could be improved using laser-leveling techniques to reduce the impact of the field micro-topography. Sanchez et al. (2009) analyzed the effects of different irrigation techniques on the performance of furrow irrigation, and the results proved that the irrigation performance could be significantly improved by selecting reasonable values for the discharge and cutoff time. Gillies et al. (2011) improved the performance of furrow irrigation by optimizing the cutoff time according to the soil infiltration variability. Reddy et al. (2013) analyzed the effects of discharge changes on irrigation performance, and the results indicated that the performance of furrow irrigation could be significantly improved by selecting a reasonable discharge. Chen et al. (2013) improved the performance of border irrigation by optimizing the length and width of the field, and the results indicated that the irrigation performance of the optimized border size average increased by 26.7% compared with that before optimization. Akbari et al. (2018) improved the performance of irrigation by optimizing the field size by using a metaheuristic algorithm. Smith et al. (2018) used the maximum application efficiency as an objective and a tail-water rate less than 5% as a constraint; the results proved that the irrigation performance could be significantly improved by selecting a reasonable cutoff time. Salahou et al. (2018) analyzed the influences of discharges per unit width and the cutoff time on the performance of border irrigation and optimized the cutoff times of different discharges per unit width on the basis of field experiments. Xu et al. (2019) proposed an optimal combination of the cutoff time and discharges per unit width in their study area through irrigation experiments of different crop growth stages. The aforementioned research results have improved the design and management of border irrigation systems and have contributed to the improvement of irrigation performance. However, these studies have mainly focused on field scales, resulting in limitations on the applications of these research results at an irrigation district scale. The reasons are the large area of the irrigation district and the soil physical parameters may have significant variations, making the determination of infiltration parameters on irrigation district scale more difficult than that on field scales.

Therefore, the Hetao irrigation district (HID) was selected as a typical research area in this study on the basis of soil physical parameters (soil particle content and bulk density) measured at 86 sampling points. The objectives of this study are (1) to analyze the spatial variability characteristics of the soil particle content and bulk density in the HID, (2) to estimate the soil infiltration parameters of the Kostiakov equation at different sampling points with HYDRUS-1D, and (3) to propose the optimal layout patterns of border size under various combinations of different typical soil textures and field slopes.