# Effect of Soil Texture on Water Movement of Porous Ceramic Emitters: A Simulation Study

^{1}

^{2}

^{*}

^{†}

## Abstract

**:**

## 1. Introduction

^{−1}, but exhibited the lowest WUE, approximately 24.9 kg m

^{−3}.

## 2. HYDRUS-2D Model

#### 2.1. Model Establishment

^{3}L

^{−3}]; t is the time [T]; z and r are the radial and vertical (positive upward) space coordinates, respectively [L]; and K(h) is the hydraulic conductivity [L T

^{−1}].

_{e}is the relative saturation; K

_{s}is the saturated hydraulic conductivity; θ

_{r}and θ

_{s}are the residual and saturated soil water contents [L

^{3}L

^{−3}], respectively; α is an empirical parameter [L

^{−l}] whose value is approximately equal to the inverse of the air entry value; and n and m are the van Genuchten–Mualem shape parameters.

#### 2.2. Model Parameter Settings

#### 2.2.1. Ceramic Emitters and Soil Hydraulic Parameters

_{s}, and l). In the simulation process, it is only necessary to set α to a very small value, and the ceramic emitter will remain saturated [5]. Therefore, the value of the ceramic emitter is set to 1.00 × 10

^{−8}cm

^{−1}. At this time, θs, θr, n, and l are not sensitive to the influence of the experiment results. Therefore, θs, θr, n, and l are set to 0.24, 0.001, 1.9, and 0.5, respectively. K

_{s}was set to 0.179 cm/h according to the ceramic emitter used in the verification experiment [4]. The soil hydraulic parameter setting is consistent with the two soil parameters used in the verification experiments.

#### 2.2.2. Boundary and Initial Conditions

_{0}is the initial soil water content (Table 1).

## 3. HYDRUS-2D Model Validity Verification

#### 3.1. Model Verification Experiment

#### 3.1.1. Experiment Setup

^{3}. The soil surface was covered with a plastic film to prevent evaporation from affecting the experiment results. The Markov bottle scale was read every 10 min for the first 120 min in order to draw the corresponding wet peak. The shape of the wetting front and cumulative infiltration were recorded from 0 to 12 h. The shape of the wetting front was drawn on the front of the polymethyl methacrylate panel every 30 min. The cumulative infiltration is equal to the product of the cross-sectional area and the difference in the water level in the Mariotte bottle.

^{−3}was taken from a wheat field in Yangling, Shaanxi Province, China. H-soil with a bulk density of 1.35 g cm

^{−3}was taken from an apple forest in Yulin City, Shaanxi Province, China. The soils were collected between a 0-30 cm depth and were air-dried, crushed, mixed, and passed through a 2 mm sieve. Soil particle composition was determined using a laser particle size analyzer (MS2000, Malvern, UK). L-soil (sand: 43%, silt: 31%, clay: 26%) was classified as silty loam, and H-soil (sand: 72%, silt: 19%, clay: 9%) was classified as sandy loam [17]. The soil water retention curve was determined by a high-speed freezing centrifuge (CR21G PF, Hitachi, Japan), and the soil hydraulic parameters [15] were fit using the RETC code [18]. Saturated soil hydraulic conductivity was measured using the falling head method (Table 1).

#### 3.1.2. Simulation Effectiveness Evaluation

_{i}is the model simulation value; M

_{e}is the measured value; and $\overline{M}$ is the mean measured value.

#### 3.2. Model Verification Results

## 4. HYDRUS-2D Model Application

_{s}) and water retention parameters (θr, n, and l) are computed using the saturated water content, as well as the clay and sand contents [20]. Field capacity is calculated by the method described by Twarakavi et al. [21].

#### 4.1. Infiltration Characteristics

#### 4.1.1. Cumulative Infiltration, Discharge, and Matrix Potential

^{3}), and 0.28 L, respectively (Table 4). This is primarily because the clay content in these soils is too high, so the contact area between the soil particles is large and the pores are small, reducing the saturated water conductivity, increasing the difficulty of soil water diffusion, and decreasing the cumulative infiltration. The cumulative infiltration of loam is 1.28 L. Although the saturated hydraulic conductivity of loam is smaller than that of sand, the cumulative infiltration is the largest.

^{3}/cm

^{3}for the 12 kinds of soils, which is provided in HYDRUS. Therefore, for the same soil texture, such as L-soil (silty loam) and silty loam, the measured saturated water content is higher, resulting in a larger cumulative infiltration.

#### 4.1.2. Wetting Front

#### 4.2. Optimization Layout of Porous Ceramic Emitters in Sandy Soil

^{3}/cm

^{3}(Table 1). After 60 h, the clay layer was completely saturated. At this time, water began to migrate downward through the clay layer. The soil water content below the clay layer was already around 0.11 cm

^{3}/cm

^{3}, and deep percolation began to occur at 120 h. The deep percolation rate (deep percolation rate = deep percolation discharge/irrigation amount ×100%) was 5.0%. Without the treatment of the clay layer, the deep percolation rate was as high as 17.8%. Therefore, in the area where the soil texture is sandy and a ceramic emitter is used for irrigation, the use of a clay layer can reduce deep percolation and improve the water use efficiency.

^{3}cm

^{−3}and 0.33 cm

^{3}cm

^{−3}, respectively; however, the cumulative infiltration of the emitter in the sandy loam is significantly higher than in the PAM-mixed sandy loam, which is 36.1 L and 19.5 L, respectively, indicating that more irrigation water in the sandy loam migrates to the deeper layers, resulting in deep percolation. Deep percolation rates in the two soils are 42.7% and 8.2%, respectively. Therefore, the use of a water retention agent can significantly improve soil water retention and reduce the risk of deep percolation.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 4.**Graph showing emitter discharge and the soil water potential around the emitter in the loam and sand through time.

**Figure 5.**Images showing the wetting front for different soil textures after 12 h ((

**a**) clay, (

**b**) clay loam, (

**c**) loam, (

**d**) loamy sand, (

**e**) sandy loam, (

**f**) sand, (

**g**) sandy clay loam, (

**h**) sandy clay, (

**i**) silt, (

**j**) silty clay loam, (

**k**) silty clay, (

**l**) silty loam).

**Figure 6.**Images showing the change in wetting front at different times in sand above a clay aquifer ((

**a**) 12 h, (

**b**) 24 h, (

**c**) 36 h, (

**d**) 48 h, (

**e**) 60 h, (

**f**) 120 h).

**Figure 7.**Wetting front for a ceramic emitter buried in sandy loam and PAM mixed sandy loam after 120 h ((

**a**). Sandy loam; (

**b**), Sandy loam with water retaining agent).

Soil Type | θr (cm ^{3} cm^{−3}) | θs (cm ^{3} cm^{−3}) | α (m ^{−1}) | N (-) | Ks (cm h ^{−1}) | Field Capacity (cm ^{3} cm^{−3}) | Initial Pressure Head h_{0} (cm) |
---|---|---|---|---|---|---|---|

L-Soil | 0.08 | 0.46 | 0.006 | 1.61 | 0.08 | 0.37 | −3000 |

H-soil | 0.08 | 0.49 | 0.007 | 2.22 | 0.68 | 0.25 | −8562 |

**Table 2.**Statistical indicators of measured and simulated discharge and wetting front in two different soils.

Statistical Indicators | Discharge | Wetting Front | ||||
---|---|---|---|---|---|---|

CRM | RMSE | NRMSE | CRM | RMSE | NRMSE | |

L-soil | −2.00% | 0.05 | 0.26 | 1.5% | 0.17 | 0.02 |

H-soil | −0.02% | 0.04 | 0.07 | 9.9% | 1.77 | 0.11 |

Soil Texture | θr (cm ^{3} cm^{−3}) | θs (cm ^{3} cm^{−3}) | α (m ^{−1}) | N (-) | Ks (cm h ^{−1}) | Field Capacity (cm ^{3} cm^{−3}) | Initial Pressure Head (cm) |
---|---|---|---|---|---|---|---|

Sand | 0.045 | 0.43 | 0.145 | 2.68 | 29.7 | 0.067 | −3000 |

Loamy Sand | 0.057 | 0.41 | 0.124 | 2.28 | 14.6 | 0.094 | −3000 |

Sandy Loam | 0.065 | 0.41 | 0.075 | 1.89 | 4.42 | 0.139 | −3000 |

Loam | 0.078 | 0.43 | 0.036 | 1.56 | 1.04 | 0.220 | −3000 |

Silt | 0.034 | 0.46 | 0.016 | 1.37 | 0.25 | 0.286 | −3000 |

Silty Loam | 0.067 | 0.45 | 0.02 | 1.41 | 0.45 | 0.272 | −3000 |

Sandy Clay Loam | 0.100 | 0.39 | 0.059 | 1.48 | 1.31 | 0.227 | −3000 |

Clay Loam | 0.095 | 0.41 | 0.019 | 1.31 | 0.26 | 0.295 | −3000 |

Silty Clay Loam | 0.089 | 0.43 | 0.010 | 1.23 | 0.07 | 0.348 | −3000 |

Sandy Clay | 0.100 | 0.38 | 0.027 | 1.23 | 0.12 | 0.306 | −3000 |

Silty Clay | 0.070 | 0.36 | 0.005 | 1.09 | 0.02 | 0.336 | −3000 |

Clay | 0.068 | 0.38 | 0.008 | 1.09 | 0.2 | 0.34 | −3000 |

Clay | Clay Loam | Loam | Loamy Sand | Sandy Loam | Sand | Sandy Clay Loam | Sandy Clay | Silt | Silty Clay Loam | Silty Clay | Silty Loam | |
---|---|---|---|---|---|---|---|---|---|---|---|---|

Aspect ratio (%) | 97.34 | 94.97 | 97.49 | 125.16 | 108.85 | 148.96 | 97.19 | 93.23 | 95.02 | 94.58 | 83.84 | 96.07 |

Cumulative infiltration (12 h) (L) | 0.28 | 0.73 | 1.28 | 1.01 | 1.23 | 0.94 | 0.73 | 0.25 | 1.00 | 0.40 | 0.07 | 1.23 |

Soil Texture | θr (cm ^{3} cm^{−3}) | θs (cm ^{3} cm^{−3}) | α (m ^{−1}) | n (-) | Ks (cm h ^{−1}) |
---|---|---|---|---|---|

Sandy loam | 0.083 | 0.312 | 0.016 | 1.594 | 2.73 |

PAM-mixed sandy loam | 0.145 | 0.353 | 0.030 | 1.561 | 2.39 |

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**MDPI and ACS Style**

Cai, Y.; Zhao, X.; Wu, P.; Zhang, L.; Zhu, D.; Chen, J.
Effect of Soil Texture on Water Movement of Porous Ceramic Emitters: A Simulation Study. *Water* **2019**, *11*, 22.
https://doi.org/10.3390/w11010022

**AMA Style**

Cai Y, Zhao X, Wu P, Zhang L, Zhu D, Chen J.
Effect of Soil Texture on Water Movement of Porous Ceramic Emitters: A Simulation Study. *Water*. 2019; 11(1):22.
https://doi.org/10.3390/w11010022

**Chicago/Turabian Style**

Cai, Yaohui, Xiao Zhao, Pute Wu, Lin Zhang, Delan Zhu, and Junying Chen.
2019. "Effect of Soil Texture on Water Movement of Porous Ceramic Emitters: A Simulation Study" *Water* 11, no. 1: 22.
https://doi.org/10.3390/w11010022