Analysis of Several Discharges – Durations-Drip Line Placements Under Mango Trees “ Tommy Atkins ” ( Magnifera Indica L . ) In Zabid Valley , Tihama-Yemen

Jamil Ahmed. The wetted volume of root area is one of the most important parameters for irrigation efficiency in the drip irrigation. Three durations (short – moderatelong duration) were compared with supplied 40, 60 and 80 L respectively. Three discharges (8, 16, and 32 l/h) were used and four treatments were tested for each discharge: one dripper, two drippers, four drippers with a looping of 20 cm and 40 cm around the trunk. The case of discharge 8 L/h with irrigation duration (10 h) in the treatment four drippers with a looping 40 cm around the trunk was superior and given the best percentage of root wetted area, 100% of the effective root area, as well as, an average volumetric water content and a coefficient of uniformity were 26% and 87%, respectively. Also, the saved water was 65.5 % compared to surface irrigation.

The wetted volume of root area is one of the most important parameters for irrigation efficiency in the drip irrigation. Three durations (shortmoderatelong duration) were compared with supplied 40, 60 and 80 L respectively. Three discharges (8, 16, and 32 l/h) were used and four treatments were tested for each discharge: one dripper, two drippers, four drippers with a looping of 20 cm and 40 cm around the trunk. The case of discharge 8 L/h with irrigation duration (10 h) in the treatment four drippers with a looping 40 cm around the trunk was superior and given the best percentage of root wetted area, 100% of the effective root area, as well as, an average volumetric water content and a coefficient of uniformity were 26% and 87%, respectively. Also, the saved water was 65.5 % compared to surface irrigation.

Introduction:-
In arid and semi-arid areas, water resources are limited and scarce (e.g. Yemen), the selection of the appropriate irrigation method in term of water use efficiency and yield is very important. Drip irrigation offers unique agronomical, agrotechnical, and economical advantages for the efficient use of water. In Yemen 90 % of the total water consumed for irrigation and 99 % of agricultural crops are irrigated by traditional methods (flooding) with very high water losses. Hence, Irrigation efficiency is very low 40-45 %, the modern irrigation methods (sprinkler, bubbler and drip irrigation) are used in only 1% of the total irrigated area (FAO, 2012). Mango tree in Yemen has spread widely as a result of the economic profits and food as well as their adaptation to the current environmental conditions in Yemen. The mango crop cultivated area occupies about 25842 hectares and represents 38% of the total area of fruit cultivation. A mango production by Yemen about 383107 (Mt), in the Tihama plain where was conducted, our experimentation, an area of the mango crop occupies about 10936 hectares which represents 11 % of the total irrigated area (MAI, 2013). The mango tree in The mango crop area reaches about 25842 hectares and occupies 38% of the total area of fruit cultivation. In The mango farms are irrigated by flooding irrigation. Surface irrigation is the main practice in the mango farms, the amount of water applied to mango trees is about 25563 m 3 / ha / season. Bithell et al. (2011) estimated the total water use of mango crops to be 204.4 mm (2044m 3 ). As for the net mango water use, the average daily rates ranged from 0.114m 3 /tree/day for drip irrigation and 0.172 m3/tree/day for surface irrigation (Al-Amoud et al., 2015).
Trickle irrigation is one of the most efficient methods and the system usually makes use of saving water supply in order to apply the precise amount of water to the root zone. It is planned to deliver frequent light applications of water to wet only portions of the soil (Al-Qinna and Abu-Awwad, 2001).
Advantages and characteristics of the drip irrigation system were analyzed by many researchers (Dagdelen et al., 2009;Fernandez-Galvez, 2006;Simonds, 2006;Phene, 1991;Phene et al., 1992), the drip irrigation offers a great potential to improve water management by improving crop yield and quality using less water, and by localizing fertilizer and chemical. Matter. (2007), observed that the average yield of mango under surface drip irrigation and sub-drip irrigation increased by 15 % and 26 % respectively in comparison to surface irrigation (furrow). Moreover, total water consumed under drip irrigation was 54.22% less than that of furrow irrigation methods (Soomro et al., 2015). Tagar et al, (2012) found that Drip irrigation method saved 56.4% of water and gave 22% more yield as compared to that of furrow irrigation method. Ibragimov et al, (2007) reported that yield was increased by 18-42% and water use efficiency increased by 35 to 103% under drip irrigation system. Trickle (drip) irrigation used 60% less water than surface irrigation whereas production was respectively 17.755 Ton /ha compared 10.715 Ton /ha of surface (Thabet, 2013). In drip irrigation takes wetted volume of the root area area of great importance, (Mirjat et al, 2011) observed that the decrease wetted area of the root area of mango trees causes a decrease of the productivity. The size of the wetted soil volume under emitters is an important field characteristic in trickle irrigation system design (Revol etal.,1991 Neshat and Nasiri, 2012), These studies showed that the volume of the wetted area is influenced by many factors, include soil physical properties, soil initial humidity, as well as emitter discharge rate , durationof application , crop root characteristics and evapotranspiration. For the wetted area, most engineers agree on a minimum of 33% and maximum of 67 % (FAO, 2002). Keller and Blienser (1990) reported a percentage wetted ranged between 50-60 % for a low rainfall area and 40% in a high rainfall area. Irrigation management depends on some parameters, such frequency, irrigation duration, dripper's discharge and spacing and the placement of drip tubing (Skagge et al., 2004). Thorburn et al, (2003) they concluded that among the distance of drip irrigation, the ratio of flow, the wet characteristics of soil and period irrigation should be a harmony in the drip irrigation for improvement of efficiency of consumption water and mineral material. There are numbers of configuration designed to increase the percentage wetted area and still be economical (double lateral, pigtail, zigzag, looping and spaghetti tubes) (Merkley and Allen, 2004). The wetted soil volume under emitters is an important field characteristic in trickle irrigation system design (Revol et al., 1991). The boundaries of the wetted soil volume where the volume of wetted soil that was above the field capacity of soil (Gençoglan and Yazar, 1998). The restricted volume of wetted soil under trickle irrigation and the depth-width dimensions of this volume are of considerable practical importance. The volume of the wetted soil represents the amount of soil water stored in the root zone, its depth dimension should coincide with the depth of the root system while its width dimension should be related to the spacing between emitters and lines, thus, the volume and geometry of the wetted soil under an emitter should become an objective rather than an end result of the design process (Zu, 1996).
The knowledge of root distribution of agricultural crops enables accurate decision-making for a rational and sustainable use of cultural practice such as soil and water management and crop fertilization. The distribution of roots of -Tommy Atkins‖ mango evaluated by Marcelo al., (2014) who have observed that the highest density of the root system is concentrated from 0.50 to 1.50 m distance from the trunk and 0.20 to 0.9 m depth in the soil. Experimentation was conducted in an 11 and 12 years age orchard in a sandy soil under drip irrigation. Also, Choudhury et al., (1992) observed that most of roots were found at distances of 0.3 m to 1.6 m from the trunk and the depths from 0.3 m to 0.9 m.
There are numbers of configuration designed to increase the percentage wetted area and still be economical (double lateral, pigtail, zig-zag, looping and spaghetti tubes) (Merkley and Allen, 2004). For the best particles of drip irrigation leading to high efficiency of mango irrigation.
The objective of this paper was determined the optimal irrigation duration under drip irrigation with a better discharge and the design of the drip line around trees. In Tihama, research in the field of drip irrigation has not been studied extensively. Our research will be a good start of the spread of the drip irrigation techniques in Yemen.

Materials and methods:-Experimental site:-
The experimental field was conducted during September, October, November and December 2014 in a farm (latitude 14° 13' 10.71‖N, longitude; 43° 21' 33.01‖E and an altitude of 127 m), located in Zabid valley, in the southern part of the Tihama plain in the west of Yemen. It's an arid area characterized by an annual average rainfall of 100 mm. In winter, the average minimum and maximum temperatures are respectively 20 °C and 29.8 °C, while in the summer; the average values are 38.8 °C and 45 °C. The data were recorded on the Jerbah Station, nearby the site. The soil particle size distribution was 75 % sand, 7.2% silt and 17.8 % clay (sandy loam). The bulk density and porosity were 1.5g/m 3 and 43%, respectively. The volumetric water content at field capacity and at permanent wilting point where 21% and 9% respectively. The saturated hydraulic conductivity is about 9 cm/h. Water for irrigation was pumped from the well and salinity (EC) was 0.92dsm -1 .
Irrigation treatments:-A drip irrigation system was designed and installed on the twelve trees in the farm, four trees for each discharge the trees were 10 years old and spacing 6 × 6 m. Four treatments were tested, one dripper next to the trunk tree (1d), two drippers on both sides of the trunk tree (2d), four drippers around the trunk with a looping spacing of 20 cm (4d-20cm), four drippers around the trunk with a looping spacing of 40 cm (4d-40 cm) and supplied water was 80, 60 and 40 liters for each discharge and treatment (Table 1) and ( Fig.1 Three irrigation durations were adopted and the same amount of water was supplied for each irrigation duration. Long irrigation duration, 10 hours for the discharge 8 L/h, 5 hours of the discharge 16 L/h and 2.5 hours for the discharge 32 L/h, moderate irrigation duration 7.5 hours for discharge 8L/h, 3.75 hours of the discharge 16 L/h and 1.9 hours of the discharge 32 L/h and short irrigation duration, 5 hours of the discharge 8L/h, 2.5 hours of the discharge 16 L/h and 1.25 hours for the discharge 32 L/h. In our case, The canopy diameter (R) of the tree is about 3.5 m The daily water value supplied by the tree is an average calculated using Eq. (1). With ET 0 = 4.9, K C = 0. 85 and K r = 0. 54, trees spacing 6× 6 m. A value of 80 L/day was used in our application V R = 1.5 × 1.5 × 3.14 × 0.9 = 6.4 m 3 ~7m 3 Where, root depth of 0.9 m and the distance roots from the trunk 1.5 m (Santos et al., 2014). Percentages of the wetted area of the root area ( P W %) was estimated as follows: (6) Where V R = soil volume of total root area (m 3 ).

Average depth of application ( ):-
Expressing the application amount as a volume is equivalent to the average depth of application gives (Keller and Karmeli, 1974): (7) Y is moisture depletion for a drip irrigation equal to 20% (FAO, 2002) Z is depth of effective roots equal to 0.9 m (Santos, 2014), Pw % is the wetted area of the effective root area. D W = 0.2 × 120 × 0.9 ×100/100= 24 mm The wetted volume of root area (7m 3 ) was calculated by Eq.4. D W = 24/1000* 7= 0.182m 3 = 168 L each irrigation.

Water saving:-
Water saving was determined by dividing the difference in water used by bubbler over basin irrigation methods. This procedure has been adopted by Tagar

Results and discussion:-
Before the beginning of irrigation, an average volumetric water content of 17% was measured and a coefficient of uniformity of 94% was found. In this study, a soil moisture depletion of 20% was retained. This study assumes a complete coverage of total volume of the effective root area. The Iso-moisture curves were drawn by a program surfer 17, for each discharge and treatment. The wetted volume was characterized by the depth and width of wetted front (Acer et al., 2009). The width wetted was measured on the surface level from the trunk, whereas the depths wetted were the average of depth wetted at the distance 0 , 25 , 50 , 75 and 100 cm from the drippers for each discharge. They were characterized by measuring the soil moisture content by gravimetric method at the end of irrigation for each duration.

Case of short irrigation duration :-
In this case, the irrigation durations were 5 hours, 2.5 hours and 1.25 hours for the discharges 8, 16 and 32 L/h respectively. The applied water was 40 L per tree for each discharge (8, 16 and 32 L/h) and for each treatment (1d, 2d, 4d-20 cm and 4d-40 cm). Table 2 shows that the width of the surface wetted area ranged from 75 to 100 cm, the highest value was 100 cm in the case of 8 L/h and the treatment 4d-40 cm. The average wetted depth in the root area varied from 35 to 50 cm. The results were no significant differences in the average depth of the wetted front. It was seen in the Fig, 2

Average volumetric water content and coefficient of uniformity:-
In the root area, the average volumetric water content varied from 19 to 22% and all the values was near the field capacity (21%), (Table 2).on the other hand The coefficient of uniformity calculated by Eq.2, they varied between 81 and 85 %.

Percentage wetted area:-
The percentage of wetted area is low ( Table 2). It varies between 8 and 31%. These short durations 5 h, 2.5 h, 1.25 h in all the treatment can't be recommended. After (FAO, 2004) and (Keller and Bliesner, 1990), the wetted area must be ranged between 33-67%.

Case of moderate irrigation duration:-
The irrigation durations tested were 7.5 , 3.75 and 1.9 hours corresponding respectively to 8, 16 and 32 L/h. An amount of 40 L of water was supplied per tree. Table 3 shows that the width of the surface wetted area ranged from 75 to 115 cm, the highest values were 115 cm in the treatment 4d-40 cm in the discharges 8, 16 and 32L/h. The wetted front depth in the root area ranged from 40-75 the lowest value was 40 cm. The most observations illustrate that an average depth of the wetted front were approximately in all the discharges and treatments. Whereas, The widths of the surface wetted area were a superiority in the treatments 4d-40 cm and 4d -20 cm (looping), it was between 95-115 cm (

Average of volumetric water content and coefficient of uniformity:-
The average volumetric water content in the root area varied from 21 to 24%, little more than the field capacity (21%) ( Table 3). Also, The coefficient of uniformity varied between 80 and 86%. The values of average volumetric water content were increased in this case compared the short duration in the above (Table 2 and 3). The values are increased near the drippers and it decreases when moving away from the droppers laterally and vertically, (Fig.5-7). Table 3:-Widths of the surface wetted area, depths of wetted front, volumetric water content ( θ V ) and coefficient of uniformity (CU) for different treatments and discharges.

Case of long irrigation duration:-
In this case, the durations of irrigation adopted were 10 hours, 5 hours and 2.5 hours corresponding respectively to 8, 16 and 32 L/h, leading to the same supplied amount of water (80L). Table 6 presents the width of the surface wetted area ranged from 75 to 140 cm. The highest value was 140 cm in The treatments 4d-40 cm at the discharges 8 and 16 L/h. Whereas, the value was 120 cm of the treatment 4d-20 cm at the all discharges 8, 16 and 32L/h. The wetted front depth ranged from 70 to 90 cm. There are no large differences between the values (Figs, 8-10).The highest values were observed in the case of 8 L/h, it was 90 cm, on other hand, all the values were increased compared with the cases short and moderate of irrigation (Table5,6) Here too, observed that the widths of the surface wetted area increased in the treatments 4d-20cm and 4d -cm (looping) as a result of increased water irrigation applied in the long durations compared short and moderate duration for all the discharges 8, 16   The results provided that discharges 8, 16

Statistic analysis:-
The results were statistically verified by using the analysis of variance (ANOVA). Tueky test values at the 5% probability level was applied and the program of SPSS was used.
ANOVA result shows significant differences between the treatments used. We can be observed that, there were considerable differences of a Pw% of the water supplied and drippers placement (P < 0.05). There were no more significant differences in the discharge. (Table 7and 8   Irrigation scheduling and water saved:-The treatment of 4d-40cm (looping) is clearly a superior. Therefor, the irrigation scheduling was conducted at this treatment for the discharges 8 and 16L/h in the duration irrigation10h and 7.5h with water applied 80 (long duration) and 60L (moderate duration) per day, respectively. The result in the   3  3  3  3  3  3  3  3  3  3  3 3

Conclusion:-
For drip irrigation, there are several parameters must be taken into account, irrigation duration, irrigation interval, discharge, lateral designing, amount of water supplied and wetted volume of effective root area. Three irrigation durations and three discharges were applied by using four treatments 1d, 2d, 4d-20 cm and 4d-40 cm. The amounts of water supplied were 40, 60, and 80 L. Width and depth of wetted front, volumetric water content, coefficient of uniformity and percentage wetted volume were evaluated. The irrigation scheduling was done. The amount of water and drippers placed around the trunk had a significant effect on the wetted volume in the root area and saved water.
In the case of an amount of 80 L (duration 10 h, discharge 8 L/h) and the treatment 4d-40 cm, Pw was 100% and irrigation interval was 2 days and saved water was 68 % compared to surface irrigation.
For the durations 7.5 h and 3.75 h with the respectively discharges 8 and 16 L/h under the treatment 4d-40 cm, even if the Pw was 50%, saved water was 79% compared to surface irrigation.