Study of Wetting Pattern under Drip Irrigation with Varying Discharge and Irrigation Interval for the Soil of Dediapada

Drip irrigation system should be designed so that the soil volume being wetted should match the root characters. To achieve this, the shape and the dimensions of the wetted soil volume underneath drip irrigated crops, should be accurately determined. This is used for better understanding of the movement of water in soil in response to a surface point source. To understand the wetting pattern of drip irrigation under soil of Dediapada the experiment was conducted at the field of College of Agricultural Engineering & Technology, Dediapada during year 2017. The treatments of the experiment were 3 levels of emitter discharge i.e., 2, 4 & 8 LPH and 3 levels of irrigation duration i.e., 1, 2 & 3 hours. The results revealed that the horizontal wetting is higher than vertical wetting; using 8 LPH emitter with irrigation time of 3 hours gave highest horizontal and vertical wetting. From the results obtained under this study, it could be concluded that during summer season, using low emitting dripper are more beneficial due to higher vertical wetting then horizontal wetting. Keyword: Drip irrigation system, Water, Soil, Crops Research Article Cite this article: Sondarva, K. N., Jayswal, P. S., Hadiya, J. V., & Dodiya V. R. (2020). Study of Wetting Pattern under Drip Irrigation with Varying Discharge and Irrigation Interval for the Soil of Dediapada, Ind. J. Pure App. Biosci. 8(5), 227-239. doi: http://dx.doi.org/10.18782/2582-2845.7513 Sondarva et al. Ind. J. Pure App. Biosci. (2020) 8(5), 227-239 ISSN: 2582 – 2845 Copyright © Sept.-Oct., 2020; IJPAB 228 For effective design of drip irrigation systems, knowledge on the water dynamics in the soil particularly horizontal and vertical wetting front below the dripper is essential. Information about temporal evolution of the wetted volume in specific soil texture can help in establishing the optimal spacing between the emitters and the irrigation duration as a function of the soil volume where the crop roots are located (Provenzano, 2007). Drip method of irrigation helps to reduce the overexploitation of groundwater that partly occurs because of inefficient use of water under surface method of irrigation. More information about the moisture distribution pattern under a drip emitter source is necessary for efficient drip irrigation design (Hammami et al., 2002). Environmental problems associated with the surface method of irrigation like water logging and salinity are also completely absent under drip method of irrigation (Narayanamoorthy, 1997). Drip method helps in achieving saving in irrigation water, increased water-use efficiency, decreased tillage requirement, higher quality products, increased crop yields and higher fertilizer-use efficiency (Qureshi et al., 2001; Sivanappan, 2002; &Namara et al., 2005). Evidences show that many researchers have attempted to study the impact of drip irrigation (Magar et al., 1988,; Qureshi et al., 2001, Dhawan, 2002, Narayanamoorthy, 2003, Verma et al., 2004, Kulecho & Weatherhead, 2005, Narayanamoorthy, 2005, &Namara et al., 2005) and have found that drip irrigation produces the desired positive impacts. It is evidenced that the drip irrigation technology is technically feasible, particularly when the farmers depend on groundwater sources (Dhawan, 2000). Keeping these issues in view, the present paper has addressed the following important issues: 1. To evaluate the wetting pattern of varying emitter discharge with drip irrigation system. 2. To evaluate wetting pattern of drip irrigation with varying irrigation time. 3. To develop models for horizontal and vertical wetting for drip irrigation. MATERIALS AND METHODS The experiment was carried out at the field of College of Agricultural Engineering & Technology, Navsari Agricultural University, Dediapada during year 2017. 3.2 Field Experiment 3.2.1 Experimental design (a) Treatments The experiment comprising of 2 treatment and treatment combination were laid out in two replications. The details of the treatment are presented in as below First factor: Dripper discharge – 3 levels, i.e. 2LPH, 4LPH and 8LPH Second factor: Irrigation time3 levels1 hour, 2 hour and 3 hour. (b) Layout Plot design with 9 treatments replicated at two times was employed in this study. The treatments were assigned to entire design of each replication by randomization process. The detailed layout is presented in Table 1. Table 1: Details of treatment plots Sr. No Particulars Details 1 No of replication 2 2 Total no. of treatment combinations 9 3 Total number of plots 3 4 Gross plot size 2.5X15 m 5 Experimental field area 112.5 m 2 Source of Irrigation The source of water for the experiment was ground water. The diameter and depth of the bore well were 15 cm and 50 m respectively. Measurement of emitter discharge In drip irrigation layout employed for the study three types of emitter with different discharge rates were used, namely 2 litres/ Sondarva et al. Ind. J. Pure App. Biosci. (2020) 8(5), 227-239 ISSN: 2582 – 2845 Copyright © Sept.-Oct., 2020; IJPAB 229 hour, 4 litres/ hour and 8 litres/ hour. The rate of discharge from each emitter was measured using a beaker for a given time of 15 minutes. Then discharge rate of the emitter per hour was calculated..


INTRODUCTION
In India per capita water availability in the years 1991 and 2001 were 2309 and 1902 m 3 and these are projected to reduce to 1401 and 1191 m 3 by the years 2025 and 2050 respectively. Hence, there is a need for proper planning, development and management of the greatest assets of the country, viz. water and land resources for raising the standards of living of the millions of people, particularly in the rural areas. (http://www.indianetzone.com).
The total available water resources (surface and ground water) of Gujarat are estimated to be about 55,600 MCM (38,100 MCM surface water and 17,500 MCM ground water). About 88 % water is supplied for irrigation, 10% for domestic uses and 2 % for industries. The current trend of increase in water supply from all users will outstrip available supplies significantly by the year 2025.
For effective design of drip irrigation systems, knowledge on the water dynamics in the soil particularly horizontal and vertical wetting front below the dripper is essential. Information about temporal evolution of the wetted volume in specific soil texture can help in establishing the optimal spacing between the emitters and the irrigation duration as a function of the soil volume where the crop roots are located (Provenzano, 2007). Drip method of irrigation helps to reduce the overexploitation of groundwater that partly occurs because of inefficient use of water under surface method of irrigation.
More information about the moisture distribution pattern under a drip emitter source is necessary for efficient drip irrigation design (Hammami et al., 2002). Environmental problems associated with the surface method of irrigation like water logging and salinity are also completely absent under drip method of irrigation (Narayanamoorthy, 1997). Drip method helps in achieving saving in irrigation water, increased water-use efficiency, decreased tillage requirement, higher quality products, increased crop yields and higher fertilizer-use efficiency (Qureshi et al., 2001;Sivanappan, 2002;&Namara et al., 2005).
Keeping these issues in view, the present paper has addressed the following important issues: 1. To evaluate the wetting pattern of varying emitter discharge with drip irrigation system. 2. To evaluate wetting pattern of drip irrigation with varying irrigation time. 3. To develop models for horizontal and vertical wetting for drip irrigation.

MATERIALS AND METHODS
The experiment was carried out at the field of College of Agricultural Engineering & Technology, Navsari Agricultural University, Dediapada during year 2017.

Field Experiment 3.2.1 Experimental design (a) Treatments
The experiment comprising of 2 treatment and treatment combination were laid out in two replications. The details of the treatment are presented in as below First factor: Dripper discharge -3 levels, i.e. 2LPH, 4LPH and 8LPH Second factor: Irrigation time-3 levels-1 hour, 2 hour and 3 hour.

(b) Layout
Plot design with 9 treatments replicated at two times was employed in this study. The treatments were assigned to entire design of each replication by randomization process. The detailed layout is presented in Table 1.

Source of Irrigation
The source of water for the experiment was ground water. The diameter and depth of the bore well were 15 cm and 50 m respectively.

Measurement of emitter discharge
In drip irrigation layout employed for the study three types of emitter with different discharge rates were used, namely 2 litres/ hour, 4 litres/ hour and 8 litres/ hour. The rate of discharge from each emitter was measured using a beaker for a given time of 15 minutes. Then discharge rate of the emitter per hour was calculated.. Wetting pattern  Soil profile was dug up to 1m and lateral was spread on each profile. Wetting front was determined by the following methods  Wetted depth and wetted diameter was measured during irrigation at every 10 minutes to obtain data on spread of water movement in the soil profile.  Readings of wetted depth and wetted diameter were taken 24 hours after irrigation under emitters with different discharge rates by applying same amount of water to know about moisture distribution below the soil surface.  System was operated for different durations i.e., 1, 2 and 3 hours and measured the wetted depth and wetted diameter 24 hours after water application.

RESULTS AND DISCUSSION
The results of the field experiment entitled "Study of wetting pattern under drip irrigation with varying discharge emitter for the soil of Dediapada" conducted during rabi season, 2017-18 at College of Agricultural Engineering & Technology, Navsari Agricultural University, Dediapada were presented in this chapter. The wetting dimensions in clay soil under drippers of different discharge capacities during different durations with equal amount of water applied were observed. The effects of different dripper discharge capacities on wetting pattern horizontally and vertically were studied. The results were presented under the following categories.

Infiltration test
To check the infiltration capacity and infiltration rate, infiltration test was carried out for the field. The infiltration test lasts for 10 hours; it can be observed from Fig. 1 & 2 that in initial time infiltration rate was greater than the two hour later. It becomes stable about 9 to 10 hours of infiltration test.

Effect of irrigation duration on wetting pattern
The surface wetted diameter as a function of time for different discharge rates is shown in Fig. 3, 4 and 5. Results showed that the higher discharge rate produces more wetted diameter when the duration of irrigation is same. As the irrigation time increased the wetted diameter is also increased as compared to low discharging emitter. Surface wetted diameter rapidly increased in first 2.0 hours, after that it increased slowly. It increased with increase in time. Further, the asymptotic tendency of the curve indicated that at long time scale wetted diameter may take a finite value. This lateral advance behavior of wetting front is attributed to the capillary predominance effect for small discharge at the opposite of gravity effect which is more important with high discharge rates (Thabet & Zayani, 2008). The data recorded for the various emitter discharges are given below in Table  No. 2, 3 and 4. It is observed that the vertical spreading can be observed after 20 minutes. The highest wetted diameter and depth observed 47.60, 53.60, 67.00 and 7.00, 11.40, 15.40 respectively for 1 hour irrigation duration. The highest wetted diameter and depth observed 63.00, 65.00, 96.00 and 21.20, 30.40, 38.00 cm respectively for 2 hour irrigation duration. The highest wetted diameter and depth observed 70.00, 72.80, 99.60 and 36.40, 47.00, 56.80 cm respectively for 3 hour irrigation duration.     Wetted depth at different discharge rates with respect to similar irrigation time was presented in Fig 1 and 2. It indicated that with increase in the discharge rates, wetted depth increased. Maximum wetted depth was observed for 3.0 l h -1 discharge rate while minimum wetted depth was observed for 2.0 l h -1 discharge rate. The results obtained shows strong relation with results obtained by Brandt et al. (1971), Bresker et al. (1971, Kaul (1979), Mostaghimi et al. (1982), Rema Devi (1983), Vasantha Kumar (1984, Alikhan et al. (1996), Higher discharge rate had shown more wetted depth than lower discharge rate due to speed of water Haghighati (1998), Mondal et al. (2007), Pelangi and Akhondali (2008). With increase in time, spreading of water is independent of discharge rate. This behavior is attributed to the predominance of gravity effects.

Effect of emitter discharge on horizontal and vertical spreading
The diameter of wetted diameter and wetted depth were measured for different irrigation times with dripper discharge rate of 2 LPH. It was observed that the diameter was increased rapidly in the beginning and increased very slowly at later times shows correlation with the results obtained by Howell et al. (1981). Similar trend was observed for 4.0 and 8.0 LPH capacity drippers. The measured average diameters for different times were presented in Fig. 4.4 and 4.5. With increase in duration i.e., 1 hr, 2 hr and 3 hr wetted diameter and wetted depth was increased in 1.0 LPH, 2 LPH and 8LPH dripper. Maximum diameter (120 cm) and maximum depth (69 cm) were observed at 3 hr duration for the 8 lph -1 dripper. It was also observed that the horizontal wetting rate was similar for low discharging dripper while it was observed higher in case of high

Horizontal vertical
Wetting under 3 h drip irrigation time for 8LPH emitter discharging dripper. Vertical wetted depth was found about 10 minutes after initiation of irrigation till that amount of water applied were spreader over the soil surface. When the water applied to a soil of higher initial moisture content i.e. frequent water application, the moisture moved more both in the radial as well as in the vertical directions. Kheper et al. (1983) and Kyada and Munjarappa (2013).

Effect of irrigation duration and emitter discharge on wetting pattern
Correlation between maximum wetting front advance (horizontal and vertical direction) and the elapsed time is presented in Fig. 6  Results showed that the higher discharge rate produces more wetted diameter when the duration of irrigation is same. Surface wetted diameter rapidly increased in first 2.0 hours, after that it increased slowly. It increased with increase in time. Further, the asymptotic tendency of the curve indicated that at long time scale wetted diameter may take a finite value. This lateral advance behavior of wetting front is attributed to the capillary predominance effect for small discharge at the opposite of gravity effect which is more important with high discharge rates Peries et al.(2007) , (Thabet & Zayani, 2008), Acar et al. (2009) The observed and plotted data is indicating nearly uniform distribution between vertically and horizontally in Graph. 6to14. With shifting to higher discharge emitter, i.e, 2 LPH to 8 LPH, the horizontal movement or the horizontal wetted area was found greater. As the soil of the field is clay soil, the water movement below the emission point was more pronounced in horizontal direction rather than in vertical direction. As the elapsed time increase the horizontal movement is decreasing and the vertical movement is 8 11 12 14 13 speeding up. The deeper water movement suggests more water available to the roots, which is necessary for plant growth. A horizontal movement of water wills generally results in evaporation losses. Almost similar results have been reported in a numerical analysis of the different experiment by Elmaloglou andDiamantopoulos (2009), Xiao et al. (2013), Wang et al. (2014).

Modeling
With varying discharge with irrigation time, the results obtained were used for modeling purpose. By using regression analysis, various models developed for 1 hour, 2 hour and 3 hour irrigation time and also 2LPH, 4LPH and 8 LPH emitter discharge to simulate the horizontal wetted diameter and vertical wetted depth. Where, D is the wetted depth and t is elapsed time from the initiation of irrigation

Validation of developed models
Developed models for horizontal wetted diameter and vertical wetted depth give very good performance when checking for the validation. For validation of all models, observed data of horizontal wetted diameter and vertical wetted depth for 1 hour, 2 hour and 3 hour with combination of 2 LPH, 4 LPH and 8 LPH emitter discharge were used. The predicted values were derived for horizontal wetted diameter and vertical wetted depth. These values of predicted wetted diameter plotted against observed wetted diameter and predicted wetted depth against observed wetted depth. A model of 2 hour irrigation time and 2 LPH emitter discharge for the horizontal wetted diameter was found best with coefficient of determination of 0.989. And similarly models for vertical wetted depth, 2 hour irrigation duration with 8 LPH and 4 LPH was found best with coefficient of determination of 0.984 as shown in graph 16 & 17 for horizontal and vertical wetting pattern respectively.

SUMMARY
An experiment was conducted at field of College of Agricultural Engineering & Technology, Navsari Agricultural University, Dediapada to determine the wetting pattern of drip irrigation. The experiment was comprised with total 8 treatments. 3 levels of irrigation time (i.e. 1, 2 and 3 hours) and 3 levels of emitter discharge (i.e. 2, 4 and 8 LPH) were adopted. The soil type of the field was clay type. The experiment was conducted during October-Novembr-2017. The results found that due to clay type soil, vertical penetration of water was found slow. The maximum wetted depth 56.8 cm was found less than 8 LPH emitter discharge for the irrigation time of 3 hours. The maximum wetted diameter 56.8 cm was found for 8 LPH emitter discharge for 3 hours. The maximum wetted depth and wetted diameter was found 38 cm and 96 cm respectively for the 2 hours irrigation time and 8 LPH emitter discharge. The maximum wetted depth and wetted diameter was found 15.4 cm and 67 cm respectively for the 2 hours irrigation time and 8 LPH emitter discharge.

CONCLUSION
 The horizontal wetting is higher than vertical wetting using higher emitter discharge than lower emitter discharge.
 In summer crop low emitter discharge will be beneficial due to low horizontal spreading and higher vertical spreading to the crop root zone.  8 LPH emitters with 3 hours irrigation time gives highest horizontal and vertical wetting profile.  The horizontal wetting and vertical wetting can be best described by 2 nd order polynomial functions.  Model developed for horizontal wetting diameter (d) for the CAET, NAU, Dediapada field is d = 0.003t 2 + 0.557t + 12.94  Model developed for vertical wetting depth (D) for the CAET, NAU, Dediapada field is D = 0.004t 2 + 0.739t + 1.956