A clay capsule is one of the porous pipes in a sub-irrigation system that can release water near the root zone. This paper has attempted to improve the physical and hydraulic properties of clay capsules based on changing the percentage of organic matter in the raw materials. The raw material used for making clay capsules is obtained from the calcareous soil of Nasr Abad village of Gorgan, Iran. The ratio of rice bran to calcareous soil as improving hydraulic properties was 1:2, 1:5, 1: 10, 1:15, and 1:20 (kg of rice bran to kg of air-dried soil). The produced clay capsules were named G2, G5, G10, G15, and G20 respectively. The water discharge and soil water distribution of clay capsules were measured at 10, 25, 50, 80, and 100 kPa of hydrostatic pressures by a discharge-pressure automation instrument. The results showed a significant relationship between discharges of porous clay capsules and organic matter mixed with raw material. Also, the results show that with increasing organic matter percentage in the clay capsule component, the discharge of clay capsules increased. The relationship between discharges of G10, G15, and G20 with hydrostatic pressure is linear, and in G2, and G5, this relationship becomes non-linear. Meanwhile, the soil wetting shape followed a spherical trend due to the slow seepage of clay capsules. But the soil wetting shapes in G10, G15, and G20 were completely spherical, and in G5 and G2 trended to ellipsoid vertically. Finally, this is of significance for irrigating plants in arid and semi-arid regions.
Research Article
Optimizing soil moisture in subsurface irrigation system based on porous clay capsule technique
https://doi.org/10.21203/rs.3.rs-2123002/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 18 Apr, 2023
You are reading this latest preprint version
Clay pot
Hydrostatic pressure
Organic matter
Seepage rate
Soil wetness
-Introduction of sub-irrigation method that apply for irrigating plants in arid and semi-arid regions.
-Introduction of buried porous clay capsule that can release water in near root zone.
- Introduction of a solution to reduce water losses for many orchards at arid and semi-arid regions
-Introduction of the soil wetness by clay capsule types for installing into the soil.
Creating uniform and adequate soil moisture is one of the most challenging issues in irrigated lands. The use of irrigation systems with high water efficiency, such as a sub-irrigation system that provides the optimum water content of the soil, is recommended as a solution to reduce water losses (Adu et al., 2019; Cai et al., 2021) for many orchards at arid and semi-arid regions (Tesfay 2011; Bhople et al. 2014; Al-Mayahi et al. 2020). Information about soil moisture variability is also an important factor when planning sub-irrigation systems (Bhayo et al. 2018; Saefuddin et al. 2019). It is now known that more than 90% of plants require moisture equivalent to the field capacity of soil for optimal growth. Therefore, the use of new techniques to control and monitor soil moisture content in the area of field capacity will play an important role in the development of soil and water management programs under unsaturated conditions (Ashrafi et al. 2002; Vasudevan et al, 2011; Ghorbani Vaghei et al., 2015; Gebru et al. 2018; Saefuddin et al. 2019).
Clay capsule nozzle are one of the new technologies in irrigation tools that is able slowly to seepage water into soil in the range of field capacity (Bainbridge 2001; Bainbridge 2002; Abu-Zreig et al. 2006; Siyal et al. 2009; Bahrami et al., 2010; Vasudevan et al., 2011; Ghorbani Vaghei et al. 2015; Abu-Zreig et al., 2018). The clay capsule is one of the porous pipes in the sub-irrigation system that can release water in the near root zone. Buried clay capsule irrigation systems are known to be very effective in the management of water by supplying a low volume of water near the root zone, based on the water requirement of crops. As well, it is one of the most important efficient traditional methods for small farms in many arid and semi-arid regions. This system has been used for the sub-irrigation of fruits and vegetables for the last 1000 years in many small-scale dry lands of the world (Bainbridge, 2001; Siyal et al. 2009; Bahrami et al., 2010; Ghorbani Vaghei et al., 2015) and also this method of irrigation is becoming increasingly common especially in the developed nations as a way of watering and fertilizing greenhouse crops (Das Gupta et al., 2009). Buried clay pot irrigation is infrequently used in dry lands of India, Iran, Pakistan, the Middle East and Latin America where the rainfall is less than 500 mm per year (Bainbridge, 2001; Ashrafi et al., 2002; Qiasheng et al., 2007: Bahrami et al. 2010; Siyal et al., 2011; Araya et al., 2014; Bhpole et al., 2014; Ghorbani Vaghei et al. 2015).
The water flow rate of buried clay capsules is an important factor in the designation, operation, and management of the irrigation system (Jiusheng et al. 2004; Qiasheng et al. 2007; Bahrami et al. 2010; Ghorbani Vaghei et al. 2016; Bhayo et al. 2018; Saefuddin et al. 2019). However, soil water distribution pattern can be influenced by the physical and hydraulic properties of clay pots as well as the physical properties of soil (Qiasheng et al. 2007; Naik et al. 2008; Siyal and Sakaggs, 2009; Ghorbani Vaghei et al., 2016). Once the water is released into the soil, its movement depends on the physical characteristics of the soil for time, until its wetting pattern becomes completed.
The key parameters such as porosity and pore size distribution of clay capsules are used to predict the water flow rate in buried clay capsules (Cultrune et al. 2004; Naik et al. 2008; Freyburg and Schwarz, 2007; Bahrami et al. 2010). Also, the water flow rate of clay capsules is affected by several factors, such as hydrostatic pressure, saturated hydraulic conductivity of the clay capsule material, wall thickness, surface area, soil type, crop type, and evapotranspiration rate (Abu-Zreig et al. 2006; Bahrami et al., 2010; Vasudevan et al., 2011). Scientific evidence indicates that hydraulic conductivity and hydrostatic pressure of clay capsules are the most important factors in providing sufficient water to the root zone (Bainbridge, 2001; Abu-Zreig et al. 2006; Siyal and Sakaggs, 2009; Ghorbani Vaghei et al. 2016). A key important aspect of hydrostatic pressure is that the relationship between the discharge of the clay capsule and hydrostatic pressure is non-linear (Abu-Zreig et al. 2006; Qiasheng et al., 2007; Haijun et al. 2009; Das Gupta et al., 2009; Bahrami et al. 2010). Siyal and Skaggs (2009) reported that in sub irrigation with porous clay pipe, the radius of the wetted zone increased as a result of increased system water pressure. Also, Bahrami et al. (2010) who developed a fuzzy model to determine the soil wetted radius and depth based on using porous clay capsule irrigation method, reported that the wetted radius and vertical depth values at hydrostatic pressure of 25 kPa with the low discharge of clay capsules were about 13.5 and 22 centimeters, respectively. These parameters in clay capsules with high discharge rates were 14 and 45 centimeters, respectively. It means that increasing the discharge rate increased the soil wetted depth, which is a lot more than the changes in soil wetted radius (Bahrami et al. 2010).
In order to provide a good irrigation system, the engineers should have a good understanding of the discharge ability of clay capsules types. Clay capsule irrigation technology is yet to be fully studied in Iran. Moreover, the effect of organic matter percent on the hydraulic properties of clay capsules has not been widely studied and reported. This material is also important to fabricate clay capsules with light weight and porous media with a good water discharge rate. Therefore, the aim of this study is to develop and improve the seepage ability of clay capsules for providing soil moisture in the root zone by changing the phase of material. As mentioned earlier, the results of this study will help in the deployment of buried clay capsule irrigation technology not only on small-scale land of Iran, but also in arid and semi-arid regions of the world.
2.1. Experimental procedures
The raw material used for the fabrication of porous clay capsules was obtained from NasrAbad village of Gorgan city in Golestan province, Iran. The mineralogy of the raw material and the baked materials, as well as its corresponding less than 2 mm fraction, were determined by X-ray diffraction (XRD), and X-ray fluorescence (XRF) analysis. The particle size distribution of raw material was achieved by the hydrometer and dry sieving method (Gee and Bauder, 1986).
2.2. Fabrication of clay capsules
To fabricate the clay capsules, rice bran husk obtained from rice crop residuals is added to the raw material. The raw material used for making clay capsules is obtained from the calcareous soil of Nasr Abad village of Gorgan city in Golestan province, Iran. The ratio of rice bran husk to the soil used to make the clay capsules was 1:2, 1:5, 1: 10, 1:15, and 1:20 (kg of rice bran husk to kg of air-dried soil), and the produced clay capsules were named G2, G5, G10, G15, and G20 respectively. This study was carried out in the Soil Science Department of Tarbiat Modares University and the clay capsules were produced in clay capsule cells manufactured by T.M.U. Porous clay capsules with cylindrical shapes were fabricated by a clay capsules automation machine (Fig. 1). The machine delivers 20 raw clay capsules at a certain time. After preparing the raw clay capsules, they were released under atmospheric conditions for 48 hrs (air-dried) and were then placed in an electric dryer at 60 0C for 24 hrs. The clay capsules were thereafter transferred to a kiln and fired at a temperature of 980 0C for 8 hrs at a rate of 3 0C per minute (Fig. 2). The porous clay capsule dimensions were 20 cm long and 10 mm thick with regular inner and outer diameters of 1.5 cm and 3.5 cm, respectively (Fig. 3). The wall thickness and outer diameter of the clay capsules were measured by a Vernier Caliper and found to be achieved 1.5\(\pm\)0.11 cm and 3.5\(\pm\)0.20 cm, respectively. The open end of each clay capsule was covered with a plastic female coupling head to fit into an irrigation pipe.
2.3. Measurement of clay capsule discharge in laboratory
When implementing a sub-irrigation system, the clay capsule flow rate plays an important role in providing water volume to the root zone (Bahrami et al., 2010). The discharge of clay capsules was measured by Discharge-Pressure Automation Device (DPAD). The DPAD automatically measures the discharge of capsules and has double cylindrical structures that provide a test for a long time (Fig. 4). Also, it is capable of measuring accurately the discharge of the clay capsule in the range of 45- 2000ml per hr with an error of about 5ml per hour.
A is the surface area of clay capsule. D and h are the outer diameter and length of the clay capsule, respectively.
2.4. Distribution pattern of soil moisture due to the seepage of porous clay capsule
The Spatio-temporal pattern of soil moisture distribution is an important factor in the designation, operation, and management of the clay capsule irrigation system. Therefore, the main objective of this study is to recognize the ability of clay capsule types to generate different forms of soil moisture patterns during irrigation time at 25, 50, 80 and 100 (kpa) hydrostatic pressures. This part was carried out in a container (60 cm in diameter, and 100 cm in height) filled with air-dried soil. The results of this part help in choosing the appropriate depth to insert the porous clay capsules into the soil, which is also able to minimize the water evaporation from the soil surface.
Therefore, each clay capsule was placed vertically at a depth of 20 cm from the soil surface in clay loam texture and their wetness shape was recorded after 24 and 48 hours. In continued, wetted radius (r) and wetted depth (d) in the soil profile were determined for each of the 5 types of porous clay capsules at 25, 50, 80 and 100 (kpa) hydrostatic pressures.
3.1. Mineralogy of clay capsules before and after firing
Table 1 displays the results of an XRF chemical analysis of the raw materials utilized to make the clay capsule. According to Table 1, the earth-alkaline oxides (CaO and MgO) are significant in raw materials. Iron oxides and earth-alkaline oxides (CaO and MgO) play a important role in improving the physical and chemical properties of soil. These substances, according to Cultrune et al. (2004), have an impact on the porosity of bricks. Iron oxides reduced porosity while earth-alkaline elements increased porosity (Monterio and Vieira, 2004; Monterio and Vieira, 2014). Also, earth-alkaline oxides (CaO and MgO) and TiO2 confer the typical buff color to ceramic products. While, a high Fe2O3 content leads to the typical reddish color of the product (Monterio and Vieira, 2004). The earth-alkaline oxides (CaO and MgO) are more prominent than iron oxides in the raw materials, as seen in Table 1. Therefore, this phenomenon may have contributed to the baked porous clay capsules' buff light color (Fig. 5).
|
Component (%) |
raw |
Baked at 9800C |
|---|---|---|
|
L.O.I |
14.07 |
0.8 |
|
MgO |
2.78 |
3.14 |
|
Al2O3 |
12.44 |
14.39 |
|
SiO2 |
51.88 |
58.44 |
|
CaO |
11.24 |
12.42 |
|
Fe2O3 |
4.79 |
4.82 |
|
TiO2 |
0.58 |
0.67 |
|
K2O |
2.37 |
2.76 |
|
Na2O |
1.41 |
1.55 |
Several studies have been conducted to show how temperature affects the porosity of clay bricks (Newman, 1987; Bories et al., 2014; Aouba et al., 2016; Sirsuwan and Phonphuak, 2020). The research findings demonstrated that phyllosilicates' chemical structure changed dramatically as kiln temperature increased (Newman, 1987; Aouba et al., 2016). The chemical composition of clay converted to a new composition in the baking process of clay capsules at a high temperature (around 10000C). XRD analysis revealed that chlorite converted to microclinic within the raw clay capsules at 980°C (Table 2). After the firing process, the microcline is also joined together, creating large sand-like particles.
|
Component (%) |
Muscovite |
Quartz |
Dolomite |
Calcite |
Clay |
Hematite |
Albite |
|---|---|---|---|---|---|---|---|
|
G0 (Raw) |
+ |
+ |
+ |
+ |
Chlorite |
+ |
+ |
|
G0 -8-980 |
- |
+ |
- |
- |
Microcline |
+ |
- |
3.2. Physical and hydraulic properties of porous clay capsules
3.2.1. Physical properties of porous clay capsules
The raw material in G2, G5, G10, G15, and G20 had a silty clay loam soil texture. The soil texture shifted to loamy sand after being baked at 9800C temperature. The main factor altering the soil texture during baking is the occurrence of the sintering mechanism. This is caused to combine together the soil particles less than 0.002 mm. A larger soil particle can play the role of sand in sedimentation analysis (hydrometer method). In this research, the sedimentation analysis results showed that by increasing the baking temperature up to 980, the size distribution of soil particles shifted from 0.002 to 2 mm.
The physical properties of the porous clay capsules used in this study are summarized in Table (3). The bulk density and total porosity of the clay capsule were significantly affected by the baking temperature in the kiln, as shown by the results of table (3). The presence of carbonate and organic mater (rice bran husk) in the raw material is an important factor in decreasing the bulk density of baked clay capsules. The results showed that the bulk density of baked clay capsules was decreased continually, when the organic matter is progressively added in raw material compositions. During the baking process, these components decompose and release CO2 into the air. The organic matter begin to compose at about 270–350°C, and is eliminated from the porous clay capsule structure, creating voids that can play the pores role. The scientific reports showed that Organic matters such as grass, rice husk and tobacco used widely in the brick industry for saving clay material, more porosity and lowering the thermal conductivity of fired clay brick (Monterio and Vieira, 2004; Monterio and Vieira, 2014; Srisuwan and Phophouak, 2020). It helps to create a porous media with low weight and high micropores. Obviously, the addition of a very fine rice bran husk increases the clay capsule the microporosity and decreases it’s the density baked at 9800C. The most striking result to emerge from Table 3 is that more very fine rice bran husk in the G2 generates a greater pore volume compared to G20 after baking. In general, G2 and G20 baked clay capsules have the highest and the lowest porosity, respectively. The percentage of total porosity of G2, G5, G10, G15, and G20 (baked porous clay capsules) was 25.5, 22.7, 20, 15.6, and 13, respectively.
|
G2 |
G5 |
G10 |
G15 |
G20 |
|
|---|---|---|---|---|---|
|
Bulk density (kg.m-3) in raw clay capsules |
1.65 |
1.67 |
1.70 |
1.71 |
1.71 |
|
Bulk density (kg.m-3) in clay capsule after baking at 9800 C |
1.23 |
1.29 |
1.36 |
1.44 |
1.49 |
|
Total porosity (%) in clay capsule after baking at 9800 C |
25.5 |
22.7 |
20 |
15.6 |
13 |
|
Soil texture in raw clay capsules |
Si.Cl.L.a |
Si.Cl.L. |
Si.Cl.L. |
Si.Cl.L. |
Si.Cl.L. |
|
Soil texture after firing at 600 and 9800 C |
L.Sa b |
L.Sa |
L.Sa |
L.Sa |
L.Sa |
|
a and b are Silty Clay Loam and Loamy Sand. |
|||||
The hydraulic conductivity and water seepage of clay capsules are significantly influenced by their porosity (Abu-Zreig et al. 2006; Bahrami et al. 2010; Ghorbani et al. 2015; Ghorbani t al, 2016; Abu-Zreig et al. 2018 ). They reported that a higher hydraulic conductivity in the clay capsules will be correlated with higher porosity. Therefore, the seepage of the G20 is expected to be less than the G2.
3.2.2. Hydraulic properties of porous clay capsules
The saturated hydraulic conductivity was influenced by the total porosity and wall thickness of clay capsules. There was a non-significant difference in size and wall thickness, but clay capsules were of different porosity. The saturated hydraulic conductivity and seepage of clay capsules (G0, G2, G5, G10, G15, and G20) were displayed in Table 4. The clay capsules porosity was positively correlated with the amount of rice bran husk. Rice bran husk was used as organic matter in the raw material composition, when fabricating mentioned clay capsules. The porosity of clay capsules increased from G20 to G2, because of the increasing in organic matter content. The saturated hydraulic conductivity of G15 and G20 was lower than that of G2 and G5, due to their lower porosity (see Table 4). The results indicated very small or non-significant enhancement in the saturated hydraulic conductivity with increasing pressure head. So, ignoring this increase, it can be considered that the hydraulic conductivity of clay capsules was constant with increasing pressure head. The saturated hydraulic conductivity of G20 enhanced from 10\(\times\)10-3 to about 17\(\times\)10-3 (cm.h-1) with increasing hydrostatic pressure head. This increment is, however, ignorable. This porent was also observed for G15, G10, G5, and G2.This means that the saturated hydraulic conductivity is a constant physical property in the clay capsules. However, the results showed that at constant hydrostatic head, the saturated hydraulic conductivity of the clay capsule increased from G20 to G2. This phenomenon relates to adding rice bran husk to the raw material for fabricating clay capsules. Furthermore, the analysis showed that the addition of rice bran husk significantly improved the water flow properties of clay capsules.
|
Clay Capsule type |
Measured Statistics |
Hydrostatic pressure (kPa) |
|||
|
25 |
50 |
80 |
100 |
||
|
G2 |
a Qcc (l.hr-1) sd of Qcc b C.V. of Qcc c |
0.351 20.5 4.6 12.7 |
0.282 32.2 7.5 13.4 |
0.23 42.1 6.3 14.9 |
0.231 52.9 7.5 14.2 |
|
G5 |
Qcc(l.hr-1) sd of Qcc C.V. of Qcc. |
0.244 13.7 4.6 14.3 |
0.207 23.7 6.6 18.1 |
0.151 27.7 6.5 13.52 |
0.164 37.5 7.5 10.1 |
|
G10 |
Qcc(l.hr-1) sd of Qcc C.V. of Qcc. |
0.068 3.9 1.1 18.5 |
0.059 6.8 2.1 19.7 |
0.065 12.0 3.1 16.1 |
0.066 15.1 3.4 12.5 |
|
G15 |
Qcc(l.hr-1) sd of Qcc C.V. of Qcc |
0.014 0.8 0.24 10.1 |
0.011 1.3 0.26 10.6 |
0.014 2.5 0.69 17.9 |
0.015 3.5 0.69 9.9 |
|
G20 |
Qcc(l.hr-1) sd of Qcc C.V. of Qcc. |
0.010 0.6 0.17 17.1 |
0.011 1.3 0.29 12.6 |
0.011 2.1 0.40 8.6 |
0.017 3.1 0.53 7.1 |
|
G0 (Raw material) |
Qcc(l.hr-1) |
31\(\times\)10− 4 0.06 |
33\(\times\)10− 4 0.12 |
36\(\times\)10− 4 0.22 |
37\(\times\)10− 4 0.28 |
|
a is saturated hydraulic conductivity of clay capsule (cm.hr-1) b is standard deviation of the average discharge of clay capsule c is coefficient of variation of the average discharge of clay capsule |
|||||
The water discharge of G15 and G20 were low and varied from 600 to 3500 cm3.hr-1 (Fig. 6) while G10, G5, and G2 were 3900–15100, 13700–37500, and 20500–52900 cm3.hr-1, respectively. Adding 5–6.6% rice bran husk to G0 increased both the hydraulic conductivity and water discharge of G15 and G20 by about 10 times, and adding 20% rice bran husk to G0 improved both the seepage and hydraulic conductivity of G5 by about 228 times. Therefore, it can be concluded that rice bran husk has a positive effect on the porosity of clay capsules and is a good method for producing clay capsules types with different water discharge rates.
In the buried clay capsule irrigation system, the water seepage of clay capsule nozzles must also be released slowly into the soil. At this condition, it can create soil water content in the range of field capacity. This plays a vital role in choosing nozzles for sub-irrigation systems, and it is recommended that discharges of clay capsules should be less than 2000 (cm3.hr-1). According to the table (4), the discharges of G2 and G5 nozzles are not recommended to use in sub-irrigation systems. However, the G5 and G2 nozzles are suitable for installing in the surface irrigation systems. It should be noted that the relationship between the discharge of G10, G15, and G20 with hydrostatic pressures is already linear (Fig. 5) and in G2, G5, this relationship becomes non-linear. According to Fig. 5, a strong positive linear relationship was observed between G10, G15, and G20 at low hydrostatic pressure conditions from 25 to 50 kPa. On other hand, most farmers can supply water pressure of up to 50 kPa on the farm. Therefore, G10, G15, and G20 can be good choices for installing in arid and semi-arid areas.
3.3. Soil wetness by clay capsules
Soil wetting patterns and wetting rates depend on many factors, including the physical properties of the soil and the hydraulic properties of the clay capsules. Knowledge of wet zone patterns around clay capsules is a prerequisite for designing efficient irrigation systems and managing water resources.
In this study, we investigated the hydraulic properties of six clay capsule types (G0, G2, G5, G10, G15, and G20) with significantly different raw material properties.
Table 5 shows the soil wet ability of these clay capsules placed vertically in a clay loam soil texture at a depth of 20 cm from the soil surface. The effect of hydrostatic pressure was tested to assess soil moisture distribution patterns. The results showed that the soil wetting shape followed a spherical trend, which is due to the low discharge of clay capsules, in G10, G15, and G20 at 24 hours irrigation times. While the spherical wetness shape in G5 and G2 was observed at 4 hours irrigation. As time passes, the pattern of soil moisture distribution changed from spherical to elliptical in G5 and G2. Meanwhile, results revealed that the spherical soil moisture distribution shape remained constant for G10, G15, and G20 during the irrigation time up to 48 hours. In generally, the soil wetting shapes in G10, G15, and G20 was completely spherical, and in G5 and G2 trend to ellipsoid vertically.
|
Type of porous clay capsule |
Pressure (kPa) |
Wetted radius (cm) |
Wetted depth (cm) |
Irrigation time (hour) |
Water volume (litter) |
|---|---|---|---|---|---|
|
G2 |
25 50 80 100 |
68 87 88 96 |
77 100 105 112 |
4 4 2 2 |
36 58 45 59 |
|
G5 |
25 50 80 100 |
42 67 68 83 |
48 70 74 100 |
8 8 8 8 |
15 29 38 54 |
|
G10 |
25 50 80 100 |
42 68 90 100 |
49 70 97 109 |
24 24 24 24 |
19.5 31 44 59 |
|
G15 |
25 50 80 100 |
30 34 46 50 |
46 52 59 73 |
24 24 24 24 |
14 23 32.5 42.5 |
|
G20 |
25 50 80 100 |
35 45 53 68 |
36 40 50 62 |
24 24 24 24 |
11 19 28 36 |
It can be noticed from Table 5 that the soil wetness shape size had positively related to the water pressure of the irrigation system. The size of soil wetness patterns was under low hydrostatic pressure (10–50 kPa) conditions smaller than under high-pressure head (80–100 kPa) conditions. This was consistent with other findings in scientific research (Siyal and Skaggs, 2009; Ghorbani et al., 2010).
Evaluation of wetting radius and depth for G2 and G5 indicated that soil water content increased significantly after 4 h of watering, approaching soil saturation. These results indicated that G2 and G5 had no auto-regulative seepage ability during irrigation period. Therefore, suitable watering times for G2 and G5 are less than 4 and 8 hours, respectively. While elapsed irrigation times, were 24, 48, and 48 hours for G10, G15, and G20, respectively. Wetted radius and depth of G10 were more than G15, and G20 at the same watering time. The wetting radius and depth of G10 with the low pressure (25 kPa) head and the high pressure (100 kPa) head were 100 cm and 109 cm, respectively, for a 24 hour watering time (Table 5).
The water seepage of clay capsule must be done slowly into the soil. This action can be able to produce soil water content within the field capacity. In final, the results of wetted radius and depth of clay capsules showed that G10, and G15 could play a good role in plants water demand. It should be mentioned that the wetted pattern was constant after the 48 hrs passes indicating that discharge of clay capsules had been reduced, when the moisture of the soil around the clay capsule is approached saturation condition.
The present research is focused on the effect of amending soil with rice bran husk on the physical and hydraulic properties of the porous clay capsule. The discharge, saturated hydraulic conductivity, and soil wetness shape of clay capsules were also explored. The discharge and saturated hydraulic conductivity of clay capsules were significantly influenced by the ratio of very fine rice bran husk used to make the porous clay capsules. The saturated hydraulic conductivity and discharge of the clay capsules were increased with increasing in the rice bran husk content. The saturated hydraulic conductivity of different clay capsule types was constant when water pressure head increased from 25 kPa to 100 kPa, while the discharge of clay capsules had increased by about 63–80% at this condition. The higher discharge was observed in G2, G5, G10, G15, and G20 respectively. Data analysis also revealed that the soil moisture distribution was extensively affected by the discharge rate of porous clay capsules. These results indicated that G2 and G5 had no auto-regulative seepage ability during irrigation time, therefore it is not recommended in the buried clay capsule irrigation systems. It should be notified that the water must be released slowly into the soil until soil water content can be able to create in the range of field capacity. At these conditions, soil wetness shape followed a spherical trend in G10, G15, and G20, and was already constant during irrigation time up to 48 hours. While in G5 and G2, the spherical wetness shape was observed until 4 hours of irrigation, but it changed into elliptical shape over-irrigation time.
The results of this study help determine the impact depth of porous clay capsules. We recommend placing a porous clay capsule at a depth of 60 cm. At this depth, most vegetable crops and orchards have few active roots. In general, G10 and G15 can play a good role in providing plants water requirements.
Ethics Approval
All authors kept the ‘Ethical Responsibilities of Authors’.
Consent to Participate
All authors gave explicit consent to participate in this work.
Consent to Publish
All authors gave explicit consent to publish this manuscript.
Authors Contributions
All authors contributed to the study conception and design. Data collection, material preparation, and analysis were performed by Hojjat Ghorbani vaghei, Hosein Ali Bahrami, and Farzin Nasiri Saleh, respectively. The first draft of the manuscript was written by Hojjat Ghorbani vaghei and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Funding
The authors declare that no funds, grants, or other support were received.
Competing Interests
The authors declare that they have no conflict of interest and there is no relevant financial or non-financial interest to disclose.
Availability of data and materials
Not applicable.
Corresponding author
Correspondence to Hojjat Ghorbani vaghei.
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