Optimization of Depth of Placement of Lateral for Sandy Loam Soil in Western Zone of Tamil Nadu, India

doi:10.21203/rs.3.rs-2955188/v1

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Optimization of Depth of Placement of Lateral for Sandy Loam Soil in Western Zone of Tamil Nadu, India

https://doi.org/10.21203/rs.3.rs-2955188/v1

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Soil moisture patterns from emitters are important for the design and management of drip irrigation systems. The soil moisture distribution pattern around a emitter depends on depth of lateral placement, emitter spacing, duration and frequency of water application, soil physical and hydraulic properties. These patterns can be obtained by direct measurements of wetting in the field, which is site specific, or by simulations using some models. Simulation of water movement in soil is very useful for optimum management of water use. Hence, the study was conducted to optimize the depth of placement of lateral in drip irrigation. Laterals were placed at 0, 15 and 30 cm below the ground level with constant lateral spacing of 1.50 m with the combination of emitter spacing of 30 and 60 cm with 2.2 and 4 LPH dripper discharge. Soil moisture distribution pattern was studied by using gravimetric method. The study revealed that wetting front in the horizontal direction started overlapping after 6 hours in lateral spaced at 15cm depth with 4 lph dripper @60 cm apart. So the layout 15 cm depth of lateral placement and60 cm @4 lph was found better than other layouts since the losses due to evaporation and percolation were minimized.

Drip irrigation

lateral depth

wetting front

soil moisture distribution

Among irrigation methods, subsurface drip irrigation is a low-pressure, high efficiency irrigation system that uses buried drip tubes to meet crop water needs. Subsurface irrigation saves water and improves yields by eliminating surface water evaporation, deep percolation losses (Camp 1998) and reducing the incidence of weeds and disease. Soil moisture patterns from emitters are important for the design and management of drip irrigation systems. The soil moisture distribution pattern around a emitter depends on depth of lateral placement, emitter spacing, duration and frequency of water application, soil physical and hydraulic properties. (Elmaloglou and Diamantopoulos 2009). The soil moisture distribution in the field varied spatially and temporally based on soil texture, topography, crop cover and irrigation practices.(Western and Grayson 1998;Huisman et al. 2002; Grote et al. 2003). The surface wetted radius and the vertical wetted depth are proportional to the water volume applied. (Rui Zahang et al.2012). The wetted radius at the soil surface and the depth of the wetting pattern as a function of application time, emitter discharge, soil bulk density, initial soil moisture content, saturated hydraulic conductivity, and the proportions of sand, silt and clay in the soil. (Ahmed A.M 2016)The optimum installation depth of emitters in subsurface irrigation systems was reported to be between 20 and 50 cm for various soil textures (Ramezani, 2011). The shapes of soil-wetting front were almost ellipsoid and spherical for surface and subsurface drip irrigation respectively.( Hamed Ebrahimian 2013). Simonne, et al., (2006) reported that with increasing the amount of irrigation water applied to a fine sandy soil the depth and width of wetted zone significantly increased and resulted in emitter-to-emitter coverage. Elmaloglou and Diamantopoulos (2008) studied that, for the same soil, the vertical component of the wetting front is greater for smaller discharge rate than for the higher one in drip irrigation. One of the important parameter affecting water distribution to the plant in the field condition is hydraulic characteristics of drip irrigation system, therefore, it is essential to understand hydraulic performance of drip irrigation system in relation to soil moisture distribution. Based on that Mallikarjun Reddy (2018) developed the equation for predicting the wetting front in sandy soil. Installing the sub surface system at 30 cm from the soil surface is the one to be recommended as it represents the active root zone for most vegetable crops, beside it leads to a better water saving in sandy soils than that allocated at 15 cm depth. (Abdallah E. Badr.2013). soil moisture distribution were studied at different drip irrigation parameter i.e lateral spacing, depth, emitter spacing, discharge and observed that the good soil moisture distribution was observed at closely lateral spacing, emitter spacing as well as it is depend on textural classification of soil.( Kashyap Partap Singh and Nitin Changade.2022) Yuchen Li (2022) estimated the soil wetting pattern model for drip irrigation based on four easily measurable parameters (i.e., initial soil water content, saturated hydraulic conductivity, total volume of applied water, and emitter discharge rate). The vertical movement of soil moisture was greater than the horizontal movement under surface as well as subsurface drip irrigation systems. Deeper drip tape installations had a potential risk of not providing moisture to shallow rooted crops.( Bajpai, 2020). With a subsurface drip irrigation system (SDI) the placement depth of laterals, emitter spacing, lateral spacing, discharge rate of emitters and system pressure all play an important role in the soil moisture distribution pattern and in delivering the required amount of water to the plant (Assouline et al. 2002; Lamm & Trooien 2005; Elmaloglou & Diamantopoulos 2008; Bozkurt & Mansuroglu 2011; Badr & Abuara 2013). The water is delivered continuously in drops at the crop root zone and wets the root zone vertically by gravity and laterally by capillary action, thus helping to conserve water by reducing evaporative water losses in agricultural systems (Bainbridge 2001; Wei Wei et al.2010).

The wetting patterns and soil moisture distribution can be obtained by direct measurements of wetting in the field, which is site specific, or by simulations using some models. Simulation of water movement in soil is very useful for optimum management of water use. The objective of this research was to analyze the soil moisture distribution pattern for various depth of lateral placement for different emitter spacing and for different discharge in sandy loam soil to optimize the depth of lateral placement and emitter spacing to obtain the most benefit of each drop of added water.

Field experiment was conducted in sandy loam soil at irrigation water management research farm of Agricultural Research Station, Bhavanisagar, Tamil Nadu Agricultural University. The soil physical and chemical properties were analyzed and the details are given in Table 1.

Table I. Soil physico-chemical properties of experimental site:

S.No	Particulars	Values
I	Mechanical analysis
	Clay (per cent)	17.7
	Silt (per cent)	8.1
	Fine sand (per cent)	20.8
	Coarse sand (per cent)	53.4
	Textural class	Sandy loam
II	Soil physical properties
	Bulk density (g CC^− 1)	1.41
	Field capacity (per cent)	32.0
	Permanent wilting point (per cent)	14.0
	Infiltration rate (cm hr^− 1)	2.1
	Hydraulic conductivity (cm hr^− 1)	0.61
III	Chemical analysis
	Organic carbon (per cent)	0.302
	Available N (kg ha^− 1)	197.0
	Available P₂O₅ (kg ha^− 1)	9.1
	Available K₂O (kg ha^− 1)	220.0
	pH (1:2: S: W suspension).	7.2
	EC (dS m^− 1; 1:2: S: W suspension).	0.2

2.1.Experimental layout

Laterals were placed at 0, 15 and 30 cm below the ground level with constant lateral spacing of 1.50 m with the combination of emitter spacing of 30 and 60 cm with 2.2 and 4 LPH dripper discharge. The design of Experiment is FRBD with three replications. (Fig. 1). Irrigation water was applied based on daily pan evaporation. At the end of irrigation, the soil around the emitter along the lateral was dug out, and the maximum distance of the wetting front from the emitter was measured in the horizontal, vertical downward, and vertical upward directions Soil water content was measured using soil moisture meter after irrigation at different horizontal (0, 15, 30, 45 and 60 cm) and vertical distance (0, 15, 30, 45 and 60 cm) in barren field after irrigation (Zero time after irrigation), 1 hour after irrigation and 2 hours after irrigation.

3.1.Wetting front

The maximum distance of the wetting front from the emitter was measured in the horizontal, vertical downward, and vertical upward directions for all the treatments. (Fig 2 to Fig 4). This study revealed that the wetting front in the horizontal, vertical downward, and vertical upward directions was affected greatly by irrigation time. With increasing supply of water, depths and width of wetted zone soil increased. Similar trends of effects were also observed in all the depths of placement of subsurface drip irrigation system. As the irrigation time increased and the wetting patterns from two emitters started overlapping. When the wetting front reaches the soil surface, downward water movement increases.

At 0 cm depth of lateral placement, wetting front reached to a depth of 40 cm at vertical downward and horizontal direction to the distance of 25 cm after 6 hours of irrigation.

At 15 cm depth of lateral placement, wetting front reached to a depth of 40 cm at vertical downward and 15 cm upward direction, and horizontal direction to the distance of 30 cm after 24 litre of water was supplied. Wetting front was overlapped after 6^th hour of irrigation. (24 litre/emitter).At 30 cm depth of lateral placement, wetting front reached to a depth of 32 cm at vertical downward and upward direction, and horizontal direction to the distance of 35 cm after 6 hours of irrigation. There is more overlapping.

3.2.Soil water content and soil moisture distribution

Soil samples were collected after irrigation, one day and two days of irrigation at different vertical and horizontal distances.(Fig 5) Soil moisture was calculated by using gravimetric method. At 0 cm depth of lateral placement, soil moisture distribution varied from 34 percent to 20 percent immediately after irrigation. . At 15 and 30 cm depth of lateral placement 31.5 and 36 per cent of soil content was recorded immediately after irrigation. Similar decreasing pattern of soil water content was observed one day and two days after irrigation. Soil water content was found to be higher at depths where laterals are placed and it decreased as depth increases.

The study revealed that wetting front in the horizontal direction started overlapping after 6 hours in lateral spaced at 15 cm depth with 4 lph dripper @60 cm apart. So the layout 15 cm depth of lateral placement and 60 cm @4 lph was found better than other layouts since the losses due to evaporation and percolation were minimized. Optimization of depth of placement of lateral experiment revealed that the dimensions of wetting pattern under subsurface irrigation were greatly affected by irrigation time. Optimal wetting pattern by optimizing irrigation time helps to avoid excessive wetting of the soil surface and high percolation to the groundwater. Higher soil water content observed at depths where laterals are placed even after two days of irrigation indicates the high frequency of irrigation.

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No competing interests reported.

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Optimization of Depth of Placement of Lateral for Sandy Loam Soil in Western Zone of Tamil Nadu, India

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Abstract

Figures

1. Introduction

2. Methods and Materials

2.1.Experimental layout

3. Results and Discussion

4. Conclusion

References

Additional Declarations

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