Research on infiltration spread in soil of drip irrigation technique for grape leaves at the water scarce region of Viet Nam

TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 217 RESEARCH ON INFILTRATION SPREAD IN SOIL OF DRIP IRRIGATION TECHNIQUE FOR GRAPE LEAVES AT THE WATER SCARCE REGION OF VIETNAM Tran Thai Hung Tran, Vo Khac Tri, Le Sam ABSTRACT The technique of drip irrigation is a solution of water saving for crops in the scarce region. Water is supplied on the soil surface directly, continuously and regularly by drippers and then it infiltrates into the cultivated soil layer to ensure that plants will grow and develop well. During the experimental process of researching on soil moisture of drip irrigation technique to determine the suitable irrigation schedule for Grape Leaves at the water scarce region, the authors carried out the experiment and observed infiltration spread. Based on calculated and observed results, the authors have proposed correlation of parameters as follows: infiltration depth, average radius of wetting front on horizontal direction, irrigation water amount versus time, velocity of horizontal (vr) and vertical (vz) permeability of drip irrigation technique. The correlation coefficients of parameters are high (R2 from 0.906 to 0.9899) and conformable to research on soil moisture dynamic in order to determine the suitable irrigation schedule for Grape leaves in particular and for terrestrial plants (with short roots) in general at the water scarce region of the South Central region of Vietnam. Keywords: Correlation; Drip Irrigation; Infiltration; Irrigation Schedule; Permeable Velocity 1. INTRODUCTION The experimental analysis results of water infiltration spread in soil (H. Darcy, 1885), (Green and Anpt, 1911), (Kostiakov, 1932), (Phillipe, 1957) have been showed that the infiltration process was divided into two phases: unstable infiltration (absorbent) and stable one. Water spread in soil depends on soil type, structures and irrigation techniques. For different types of cultivated land, permeability and moisture reserves in soil is different, so the watering time will be varried depending on each soil type [1-3]. Irrigation methods and techniques largely influence the water infiltration process into soil. When soil is irrigated according to traditional methods, water will evenly saturate and spread from the ground to the bottom. Thus at the location situated between trees, this water will be wasted, sometimes enable weeds to grow quickly and cause negative effects on crops. Regarding the drip irrigation technique, water is provided very reasonable amount from a point on the ground through irrigation equipment, then spreads out around and bottom, with just enough water volume supplied to moisten the active roots, soil will reach optimum moisture, without causing waste water and saturation TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 218 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM excess. For each plant kind, the active roots have occupied the different volume. The development of these active roots is very important, when soil is provided adequate water and nutrients in a reasonable manner, the roots will absorb water, nutrients and air for plants to grow and develop well, creating high yield and quality product [4]. Previous studies have often focused on the aspect of crops irrigation schedule for each irrigation technique, not much attention to soil moisture dynamic in the space of the active roots. Some scientists have studied soil water movement for the traditional irrigation method (flooding irrigation, ditch irrigation, strip irrigation etc.), but there are few simulations of drip irrigation technique especially in moisture dynamic (water is supplied from a point spread around). Thus, it has caused the shortage or excess water irrigation when the optimal moisture area is larger or less than the active root space. That does not meet demands in agricultural production and reduce efficiency of water saving irrigation, especially for water scarce regions. Binh Thuan and Ninh Thuan are two provinces in the South Central region of Vietnam with the harsh climate and natural conditions, where has the lowest precipitation in the country and the unequal distribution by time (annual average is about 500-800mm). Features of water resources is scarceness, causing drought and severe water shortage for socioeconomic development, especially agriculture production. There are more than half a million ethnic minorities whose livelihoods depend on agricultural activities in this area. Due to difficult production conditions so most of the population is under the poverty and needs be improved living standards [5]. This performed research is very necessary with the aim to establish correlations between the parameters as follows: infiltration depth, average radius of wetting front on horizontal direction, irrigation water amount versus time, velocity of horizontal (vr) and vertical (vz) permeability of drip irrigation technique for researching on soil moisture dynamic in order to determine the suitable irrigation schedule for Grape leaves in particular and for terrestrial plants (with shallow roots) in general, and then it is applied into cultivating reality to avoid water wastage and get irrigation efficiency at the water scarce region of the South Central region of Vietnam. 2. MATERIAL AND METHODS Objective Researched objective was infiltration spread in soil of drip irrigation technique with irrigation frequencies as 2 days, 3 days and 4 days. The experimental model was performed at the Grape leaves farm in Thuan Quy village, Ham Thuan Nam district, Binh Thuan province. The mechanical and physical characteristics of soil have been tested in the laboratory of the Southern Institute of Water Resources Research. Approachability and methodology (1) Approach reality and theory comprehensively, combine with selective inheritance from the scientific research results of infiltration in soil and water-saving TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 219 irrigation technology for production [4]; (2) Approach structural components of the water utilization models as follows: source, transport, utilizing exploitation and application of advanced science and technology about: irrigation equipment, materials, structures, crops and modern computational software in order to analyse, select and design a experimental model at the field [2, 6]; (3) Take soil samples at various depths at the field. Analyse mechanical and physical characteristics of soil in the laboratory; Figure 1. The sketch of research approachability and methodology LEGENDS: Z: Infiltration depth (cm); R: Average radius of wetting front on horizontal direction (cm); W: Irrigation water amount (ml); T: Time (minute); Vr: Velocity of horizontal permeability (cm/minute); Vz: Velocity of vertical permeability (cm/minute). (4) Establish the experimental model, observe irrigation and infiltration spread development in soil following space (horizontal and vertical permeability) and time with irrigation frequencies as: 2 days, 3 days and 4 days. Periodically monitor infiltration spread with time step of 5 minutes/per time as: 1, 3, 5, 10, 15, 20, 25, 30,... to 200 (minutes) stop watering; then continue monitoring water spread in soil with time step as: 210, 240, 270, 300, 330 and 360 (minutes) stop observing [5, 7, 8]; TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 220 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM (5) Establish recurrent correlations between variables: infiltration depth (z), average radius of wetting front on horizontal direction (r), irrigation water amount (w) and time (t), velocity of horizontal (vr) and vertical (vz) permeability according to under research objectives proposed. (6) Collect observed data and analyze the experimental results by using Excel and SPSS16 program; 3. RESULTS AND DISCUSSION The soil at the experimental model was fine sandy with high void ratio, so water particles have moved by their own gravity component larger than soil capillary force over themselves (refer with: Table 1). When water permeates the soil, wet soil block looked like hemispherical. In initial time, water spread very fast in a circular motion on the ground, velocity of horizontal permeability (vr) was almost as fast as vertical one (vz) (permeate downward). During the next phase, velocity of horizontal permeability was smaller than vertical one. In the last phase, mostly water permeated downward and little horizontal. The infiltration spread development of each irrigation frequency in soil was as follows (refer with: Fig. 2 and Table 2): Two-day irrigation frequency (IF2): With short irrigation one, soil moisture content was still high so water trended towards the more horizontal permeability beside the vertical one (downward). In the first 20 minutes, the infiltration velocity of two directions as vertical and horizontal were rather evenly, z20 = 10.55 - 10.7 cm, r20 = 10.05- 10.25 cm, vz20 = 0.5 cm/min, vr20 = 0.46 cm/min; then the horizontal permeability trended to slow down although the vertical one was still continuing with less reduction. After 145 minutes, the horizontal velocity decreased small, vr145 was about 0.02 cm/min and lower than vertical one vz145 = 0.1 cm/min. At the stop watering time (after 200 minutes) z200 = 41- 41.45 cm, r200 = 22.35 – 23 cm, vz200 = 0.08 cm/min, vr200 = 0.01 cm/min, then water continued permeating to the depth of z360 = 43.8 - 45.4 cm and r360 = 22.9 - 23.8 cm; Three-day irrigation frequency (IF3): Water regularly permeated around and downward due to reduced soil moisture more than that one of the IF2. In the first minute, the vertical infiltration velocity (vz1 = 1.48 cm/min) was faster than the horizontal one (vr1 = 1.35 cm/min); in the next 14 minutes, the infiltration velocity was faster than that one of the IF2 and rather evenly under two directions (vertical and horizontal); in the next 30 minutes, the infiltration velocity decreased compared with that one of the IF2, z45 = 20.1- 20.75 cm, r45 = 15.5 - 15.75 cm, vz45 = 0.23 cm/min, vr45 = 0.1 cm/min; The next time, the horizontal velocity trended to slow down during vertical infiltration was still continuing with less reduction. After 125 minutes, the horizontal velocity decreased small, vr125 was about 0.02 cm/min and lower than vertical one vz125 = 0.15 cm/min. At the stop watering time (after 200 minutes), z200 = 42.8 - 43.35 cm, r200 = 20.8 - 21.2 cm, vz200 = 0.08 cm/min, vr200 = 0.01 cm/min, then water continued permeating to the depth of z360 = 44.8-46.9 cm and r360 = 21.3 -21.7 cm. Comparing with the same time step for experiment, the infiltration depth (vertical - z) in the IF3 was larger than that one of the IF2, on the contrary, the horizontal permeability (r) at the IF3 was smaller than that one in the IF2; TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 221 Table 1. Soil characteristic of the layers from 0 to 60CM Soil layer (cm) Grain size analysis Physical characteristic Descriptio n Medium Sand (%) Fine Sand (%) Coarse Silt (%) Fine Silt (%) Clay (%) Wet Density γw (g/cm3) Dry Density γd (g/cm3) Specific Gravity D Saturation S (%) Porosity n (%) Void Ratio eo (2.0 - 0.85) (0.85 - 0.425) (0.425- 0.25) (0.25- 0.106) (0.106- 0.075) (0.075 - 0.01) (0.01 - 0.005) (< 0.005) 0-20 0 4.30 47.60 41.50 1.70 0.40 0.50 4.00 1.60 1.56 2.65 8.86 40.99 0.69 Greyish brown fine sand 20-40 0 3.50 47.40 36.10 6.40 0.50 0.50 5.60 1.56 1.51 2.63 13.30 42.70 0.75 Greyish yellow fine sand 40-60 0 3.80 48.20 35.20 6.10 0.46 0.50 5.74 1.68 1.62 2.64 15.70 38.66 0.63 Greyish yellow fine sand Grain size analysis with five types: (1) Medium Sand with two grades: 2.0 - 0.85mm, 0.85 - 0.425mm; (2) Fine Sand with three grades: 0.425 - 0.25mm, 0.25 - 0.106mm, 0.106 - 0.075mm; (3) Coarse Silt with one grade: 0.075 - 0.01mm; (4) Fine Silt with one grade: 0.01 - 0.005mm; (5) Clay with one grade: < 0.005mm. TU Y EÅN TA ÄP K EÁT Q U A Û K H O A H O ÏC & C O ÂN G N G H EÄ 2016 V IEÄN K H O A H O ÏC TH U ÛY LÔ ÏI M IEÀN N A M 221 TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 222 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM Table 2. Observed results of the infiltration process of soil in six experimental times Time (minute) Two-day irrigation frequency Three-day irrigation frequency Four-day irrigation frequency W2 (a) (ml) Z2 (b) (cm) R2 (c) (cm) vz2 (d) (cm/min) vr2 (e) (cm/min) W3 (a) (ml) Z3 (b) (cm) R3 (c) (cm) vz3 (d) (cm/min) vr3 (e) (cm/min) W4 (a) (ml) Z4 (b) (cm) R4 (c) (cm) vz4 (d) (cm/min) vr4 (e) (cm/min) 1 17.5 1.4 1.3 1.39 1.32 17.6 1.5 1.4 1.48 1.35 17.7 1.6 1.5 1.63 1.52 3 52.5 3.5 3.3 1.03 1.00 52.7 3.7 3.5 1.08 1.07 53.0 4.0 3.8 1.17 1.14 5 87.5 5.0 4.8 0.78 0.75 87.8 5.3 5.0 0.83 0.75 88.3 5.7 5.3 0.85 0.75 10 175.0 8.2 8.0 0.64 0.63 175.5 8.7 8.1 0.68 0.61 176.5 9.3 8.3 0.72 0.59 15 262.5 10.9 10.5 0.54 0.52 263.3 11.3 10.3 0.51 0.46 264.8 12.1 10.5 0.56 0.45 20 350.0 13.2 12.4 0.46 0.37 351.0 13.4 11.9 0.42 0.32 353.0 14.4 12.0 0.46 0.29 40 700.0 19.8 15.8 0.27 0.12 702.0 19.4 15.2 0.24 0.11 706.0 21.3 15.1 0.29 0.11 60 1050.0 24.1 17.7 0.19 0.09 1053.0 23.8 16.9 0.22 0.08 1059.0 25.8 16.7 0.20 0.07 80 1400.0 27.7 19.1 0.18 0.07 1404.0 27.9 18.3 0.20 0.06 1412.0 29.5 17.7 0.17 0.04 100 1750.0 31.0 20.3 0.15 0.05 1755.0 31.5 19.1 0.17 0.04 1765.0 32.7 18.4 0.16 0.03 120 2100.0 33.6 21.1 0.12 0.03 2106.0 34.7 19.7 0.15 0.03 2118.0 35.6 18.8 0.14 0.02 140 2450.0 35.8 21.7 0.11 0.03 2457.0 37.4 20.1 0.13 0.02 2471.0 38.4 19.2 0.14 0.02 160 2800.0 37.8 22.1 0.10 0.02 2808.0 39.7 20.5 0.10 0.02 2824.0 40.7 19.5 0.10 0.02 180 3150.0 39.7 22.5 0.08 0.02 3159.0 41.7 20.8 0.10 0.01 3177.0 42.7 19.7 0.10 0.01 200 3500.0 41.3 22.9 0.08 0.01 3510.0 43.4 21.0 0.08 0.01 3530.0 44.6 19.9 0.09 0.00 300 0.0 44.3 23.2 0.01 0.00 0.0 45.8 21.3 0.01 0.00 0.0 47.3 19.9 0.01 0.00 360 0.0 44.5 23.4 0.00 0.00 0.0 46.0 21.5 0.00 0.00 0.0 47.5 20.0 0.00 0.00 (a) means fixed water amount was supplied for crop according to irrigation frequencies in six experimental times. (b), (c), (d), (e) mean average observed variables in six experimental times. TU Y EÅN TA ÄP K EÁT Q U A Û K H O A H O ÏC & C O ÂN G N G H EÄ 2016 222 IEÄN K H O A H O ÏC TH U ÛY LÔ ÏI M IEÀN N A M TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 223 Figure 2. The sketch of the infiltration process and soil moisture dynamic LEGENDS: (*) Minimum - Maximum infiltration depth (Z) at observed time (cm); (**) Minimum - Maximum average diameter (2R) of wetting front on horizontal direction at observed time (cm); Four-day irrigation frequency (IF4): With repeated watering time was quite long so the soil of this frequency was dryer than that one in other frequencies (IF2 and IF3) due to evapotranspiration by the ground and through the leaves, soil moisture reduced much more than that one in the IF2 and IF3 so the infiltration velocity at this IF4 was the largest, water trended to the more vertical permeability (downward) beside the horizontal one. In the first minute, the vertical infiltration velocity (vz1 = 1.63 cm/min) Have been irrigating for 20 minutes 23.6 - 25cm (**) Have been irrigating for 5 minutes 5.0 - 5.7cm (*) 2.6 – 3.1cm 9.5 - 10.7cm (**) Have been irrigating for 1 minute The ground Have been irrigating for 10 minutes 13.05 - 14.5cm (*) 15.8- 16.7cm (**) Have been irrigating 30.9 – 33.0cm 32.8 – 35.8cm 35.6 – 41.2cm The ground Have been irrigating 43.8 - 48.0cm 38.4 – 46.4cm (**) 1.38 - 1.65cm 8.2 - 9.3cm (*) 23.3 – 26.1cm (*) 41.1 – 44.9cm (*) The equal moisture line After stop irrigating 160 minutes 38.9 – 47.6cm Have been irrigating for 100 minutes Have been irrigating 37.7 - 41.0cm (*) 36.6 – 42.8cm (**) 33.6 – 35.9cm (*) Have been irrigating 37.6 – 44.8cm The ground TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 224 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM was faster than the horizontal one (vr1 = 1.52 cm/min); in the next 50 minutes, the infiltration velocity of two directions (vertical and horizontal) were rather evenly and faster than that one in other frequencies (IF2 and IF3); in the next time until water supply cessation, the vertical velocity decreased nearly equivalent with it in the IF3 but larger than that one in the IF2, conversely, the horizontal velocity trended to slow down equivalent with it in the IF3 but smaller than that one in the IF2; starting from the minute of 195th until watering cessation, water only trended to vertical permeability and less horizontal one. At the stop watering time (after 200 minutes), z200 = 44.3 - 44.9 cm, r200 = 19.15 - 20.25 cm, vz200 = 0.09 cm/min; vr200 = 0, water continued permeating to the depth of z360 = 46.8 – 48 cm and did not permeate horizontal any more. Comparing with the same time step for experiment, the infiltration depth (vertical - z) in the IF4 was larger than that one of the IF2 and IF3, on the contrary, the horizontal permeability (r) at the IF4 was smaller than that one in the IF2 and IF3. Figure 3. The infiltration process monitoring at the experimental model, Binh Thuan province Based on the results of analyzing and monitoring of the infiltration process in soil, the correlations between variables have been established: infiltration depth (z), average radius of wetting front on horizontal direction (r), irrigation water amount (w) and time (t), velocity of horizontal (vr) and vertical (vz) permeability. The established functions have high correlation coefficient (R2 > 0.90) (refer with: Table 3 and Fig. 4, Fig. 5 and Fig. 6). TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 225 Figure 4. Correlation relationships between variables of two-day irrigation frequency TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 226 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM Figure 5. Correlation relationships between variables of three-day irrigation frequency TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 227 Figure 6. Correlation relationships between variables of four-day irrigation frequency Table 3. Relationships of recurrent correlations between variables Correlation Two-day irrigation frequency Three-day irrigation frequency Four-day irrigation frequency r - z r = 7.6036ln(z) - 5.9535 R² = 0.9666 r = 6.8464ln(z) - 4.8236 R² = 0.9778 r = 6.3817ln(z) - 4,2771 R² = 0.9802 z - w z = 8.994ln(w) - 35.645 R² = 0.9258 z = 9.4504ln(w) - 38.091 R² = 0.906 z = 9.5763ln(w) - 37.842 R² = 0.9223 TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 228 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM z - t z = 9.3112ln(t) - 10.912 R² = 0.9344 z = 9.7827ln(t) - 12.068 R² = 0.9182 z = 9.9148ln(t) - 11.425 R² = 0.9313 r - w r = 4.5756ln(w) - 14.194 R² = 0.9899 r = 4.1287ln(w) - 12.086 R² = 0.9897 r = 3.7723ln(w) - 10.166 R² = 0.9857 r - t r = 4.3998ln(t) - 0.5178 R² = 0.9818 r = 3.9283ln(t) + 0.4011 R² = 0.9766 r = 3.5406ln(t) + 1.423 R² = 0.9643 4. CONCLUSIONS AND RECOMMENDATIONS Experimental results of infiltration spread were suitable for characteristic of fine sand type with high void ratio at the South Central region of Vietnam. The soil layer of 0-5cm with much evaporation had fast infiltration velocity, the layer from 5cm downward had stable one. Comparing with the same time step for experiment, the infiltration depth (vertical - z) in the IF4 was larger than that one of the IF2 and IF3, on the contrary, the horizontal permeability (r) at the IF4 was smaller than that one in the IF2 and IF3. Monitoring results have been showed that when water permeated to the soil layer containing the active roots (the IF2: z = 5-15 cm; IF3: z = 6-17.5 cm; IF4: z = 8-20 cm), velocity of horizontal and vertical permeability was large, it has been explained that the roots had sucked water (reducing soil moisture) and transpiration through the leaves to feed growing plants, concurrently the roots also created small links for water to move easily from locations with low potential to high one, and causing the infiltration velocity increased. The charts for the correlation relationship between variables showed that the established functions had rather high correlation coefficient, R2 were from 0.906 to 0.9899 suitably for research on soil moisture dynamic to determine the suitable irrigation schedule for Grape leaves in particular and dried plants (with a shallow root system) in general at the water scarce region of the South Central region of Vietnam. Special recommendation for practical production with the similar nature features, the farmers only irrigate (using the drip irrigation technique) in a period of 35-40 minutes, that will be enough for water to permeate all the active root layer with 20cm depth, or in about 90 minutes to infiltrate to the depth of 30 cm, then stop watering to avoid water waste by downward penetration and ensure water use efficiency. To reduce the water loss permeability of soil, the farmers should increase clay content, humus or colloid for the soil to keep moisture and crops grow well at the water scarce region of the South Central region of Vietnam (with similar soil conditions). Recommend further researches on infiltration spread in the condition of heterogeneous cultivated layers by depth, uneven topography, changed watertable level and impacts on crops in order to apply in practical production effectively. ACKNOWLEDGEMENTS This study was carried out in the framework of a PhD study on soil moisture TUYEÅN TAÄP KEÁT QUAÛ KHOA HOÏC & COÂNG NGHEÄ 2016 VIEÄN KHOA HOÏC THUÛY LÔÏI MIEÀN NAM 229 dynamic of drip irrigation technique in order to determine the suitable irrigation schedule for Grape Leaves at the water scarce region and the National project of research on scientific and technological solution proposal of irrigation infrastructure and running water for economic development and modern rural building of the South Central region of Vietnam. I would like to thank my organization, the Southen Institute of Water Resources Research and the farm owner at Binh Thuan province, Vietnam for their helps and support us in completing this experiment. REFERENCES 1. Tau T.K. and Dan N.T. “Soil moisture for plants”. Agriculture Publishing House. Vietnam, 1996. 2. NETAFIM. Irrigation System and Low Volume Irrigation Systems. Israel, 1994. 3. Richard H.Cuerca. 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