IMPROVEMENT IN SUB-SURFACE DRIP IRRIGATED PISTACHIO UNDER SALINE WATER USE

IMPROVEMENT IN SUB-SURFACE DRIP IRRIGATED PISTACHIO UNDER SALINE WATER USE Hossain Dehghanisanij 1 and Farshad Haji Aga Bozorgi 2 ABSTRACT Pistachio is a valuable crop in Iran and is produced mostly in arid part of the country. A study was conducted in a subsurface drip irrigated (SDI) pistachio farm in Semnan region to evaluate the impact of precision irrigation and leaching management in SDI on water distribution and salt accumulation in the soil. The treatments were three irrigation management (1) irrigation based on farmers experience as control where 3 times leaching water was applied during the growing season, (2) irrigation management based on crop water requirements estimated by Penman Montieth Model (PM), and (3) irrigation management based on PM and leaching requirement (PM+LR). Water application were recorded by flow meter and soil samples were collected from different depth and distance from the trees in different pistachio growth stages. The trees faced deficit irrigation during development growth stages in control, but in others, soil water content in the root zone was at field capacity. Based on soil water content distribution in root zone, emitter line at 1 m from the row of trees and 0.40 m under the soil surface were recognized appropriate to supply crop water needs in the root zone. Soil salinity level in PM management was less than that in PM+LR. More salt entrance by irrigation was seen under PM+LR. Where irrigation management was based on PM+LR, soil salinity was about 12 ds/m within root zone area. SAR was less in PM compared to others irrigation managements. PM+LR bring better soil water content for root trees but was not effective to leach out the salinity. Sodium concentration in PM and PM+LR where less than that in control significantly. Mg concentration in control increased during the irrigation season but that was constant in PM+LR. Ca concentration in control was constant but decreased in PM and PM+LR. The was good correlation between soil water and salinity with Na, Mg and SAR but there was no a significant relation with Ca. According to the results SDI is not able to leach out the accumulated salt from the root zone by increasing the irrigation time. A complementary irrigation water by surface irrigation or rainfall event is needed to leach out the salt from the soil at the end of irrigation season. Keywords: Subsurface Drip irrigation, Leaching, Pistachio, Irrigation managements, Semnan, Salinity. 1. INTRODUCTION In Iran, the implementation of drip irrigation system for pistachio orchards have been developed especially in Kerman and Semnan due to the tolerance pistachio to deficit irrigation and salinity in climate and geographical conditions. Semnan region where the project was implemented. The most sensitive growth stages of pistachio trees to produce better quality and quanitity product is the flowering period which is generally April-May and filling the brain is July. Water stress from mid-may to late June effect early split and smiling of pistachio. Irrigation after pollination and during fruit set may effect the number of seeds per tree. Similar to a full investigation of pistachios, watering should be done well generally in late August and early smiling September. 1 Associate Professor, Agricultural Engineering Research Institute (AERI), Agricultural Research Education, and Extension Organization (AREEO), Karaj, IranEmail:dehghansanij@yahoo.com 2 Master Student in Shiraz University. Shiraz, Iran. Email: bozorgi_ff@yahoo.com 1

According to the studies during periods of growth of pistachio trees in Semnan, first crop growth stage is 50 days from 21 March, development stage is 60 days from May 11, middle stage is 70 day 21 July and late stage 60 days from 1 October (Farshi et al., 1997). During the period of growth of pistachio trees is about 240 days from beginning to harvest. In SDI soil surface remain and evaporation from the soil surface decreases. Reducing evaporation from the soil surface may caused increasing transpiration, canopy level, the openness Asthma-ta and increased photosynthesis, resulting in increased water use efficiency (WUE). Eslami (2006) studied the possibility of using saline water (8 ds/m) by SDI for 4 years. He maintained the depths of drip laterals as 50 and 70 cm. The results of the study showed no clogging in the drippers and less soil water evaporation (hence, less salt accumulation also) whjen the depth of drip lateral was 70 cm. Trenton et al (2008) observed highest salt concentration of 11 ds/m 3 cm below the soil surface. Between 3 cm and 1.05 m, soil salinity significantly reduced and remained stable. It may be noted that the depth of insertion of drip laterals was 18 and 25 cm and salinity of water was 1.5 and 2.6 ds/m during growing seasons. Soil and water salinity is a major problem for of agriculture in the world. Under SDI salt accumulate within the wetted zone where the concentration is higher at or near the soil surface and between the drip lateral. In DI the concentration of salt on the soil surface or near it, causing problems for germination while with accurate design and proper management these problems eased placed (Enciso et al. 2008) Burt et al. (2003) studied the distribution of minerals in the SDI for pistachio and showed that accumulation of salt on the installation depth of 30, 40 and 60 cm. accordingly, the accumulation of salts in the root zone lie below the in the depth of roots while for the other depth salt accumulated close to the soil surface. The present study was conducted in a subsurface drip irrigated pistachio farm in Semnan region to evaluate impact of precision irrigation and leaching management on water distribution and salt accumulation in the soil by monitoring water and salinity. 2. MATERIALS AND METHODS 2.1 Study area Water shortages in Iran, and the need of its optimum utilization, prompted water authorities and farmers to use modern irrigation systems such as drip irrigation (DI). After DI subsurface drip irrigation (SDI) developed for even better water management. The study was done in 2 ha parcel of a 100 ha 10-year old pistachio farm. The distance between the tress was 3 m and the average distance between the tree rows was 7 m. Pistachio trees are resistance to soil salinity and alkalinity. In Iran, pistachio planted in desert and water deficit areas need more efficient use of water. In this research, irrigation drip lateral installation depth was 40 cm. Each row of trees was served by two drip lateral, each 1 meter from the tree row. 2.2 Monitoring soil water content and salinity To measure soil water content and salinity in accordance with the terms of growth stages: initial, development, middle and late growth period, soil samples were 2

collected before and 24 hr after irrigation at three depths of 25-0, 50-75 and 100-75 cm during periods of plant growth (Figure 1 and Figure 2). Figure 1. Soil sampling postion within the trees Figure 2. Samples of hole for soil sampling A part of the orchard was selected to apply 3 irrigation treatments. The irrigation management treatments were: 1. irrigation based on farmers experience as control where 3 times leaching water was applied during the growing season (control), 2. irrigation based on crop water requirements (Penman Monthieth; PM) and 3. irrigation based on PM and leaching requirement (PM+LR). 3

3. RESULTS AND DISCUSSION In order to show soil water content and salinity variation in the soil before and after irrigation, for crop growth stages and irrigation management Surfer software used to draw soil water content, EC and SAR. 3.1 Moisture content variation in the soil: To show the soil water content variation before and after irrigation within development growth stage the days 97 and 98 after first irrigation was selected as a representative. As a result most rate of soil water content after irrigation were concentrated around the drip lateral line and close to the emitters. The soil water content below the emitters was higher than that upper part of emitters (Fig. 3a and 3b). Control PM Figure 3a. Soil water content (%) before irrigation on 97 days before first irrigation for different management of control, irrigation based on Penman Montheith (PM) model and PM plus and leaching requirement (PM+LR). 4

Based on the Figure 3. most values of soil water content can be seen in PM and PM+LR irrigation management. Since soil water content in field capacity was about 12%, under control management the trees was faced stress before irrigation which observed even 24 before irrigation. Soil water content under PM and PM+LR was been in a proper condition. Control PM Figure 3b. Soil water content (%) before irrigation on 98 days before first irrigation for different management of control, irrigation based on Penman Montheith (PM) model and PM plus leaching requirement (PM+LR). The day 151 and 152 were selected as representative for before and after irrigation in the middle crop growth stage. Based on the results the soil water content in all the irrigation management was higher than filed capacity before irrigation. Which shows irrigation duration for all 3 management should be higher than amount needed. Also it can be concluded that PM may have over estimate of crop water requirement. 5

Also in middle crop growth stage continuous soil water content profiles between the two irrigation drip laterals in all three managements are established to demonstrate the suitability of the drip lateral spacing. In this period the highest amount of soil water content in the third management and the lowest average soil water content showed in control management. The day 207 and 208 after first irrigation event were selected as representative for before and after irrigation in the end crop growth stage.in this crop growth stage control and third irrigation management (PM+LR) soil water content under the drip lateral was higher before and after irrigation. The distribution of soil water content because water moves upward caused water evaporated and soil water content in upper part be higher than lower part. However, about forms of irrigation water distribution after irrigation event expected a continuous soil water content profiles formed between the two drip laterals line which expectations have been met in all three managements. This demonstrates the suitability of the drip lateral with irrigation irrigation interval. 3.2. Salinity variation in the soil: To study the condition of soil salinity profiles before and after irrigation, ECe in days 97 and 98 after first irrigation which is coincided with the most important pistachio plant growth period were drawn. According to the result, soil salinity in all management is more than pistachio threshold level which shows pistachio is resistance to more than 8 ds/m in soil. (Razavinasab et al., 2011 1390). The results are agreed with (Sayeri et al.,2007 1386) which studied the impact of salinity on pistachio in Rafsanjan, where is similar to research site. Salinity distribution before and after irrigation is shown in Fig 4. According to the Fig. 4 the value of Ec (electrical conductivity) after watering dropped between drip lateral s in the first management (control) but there is some increase around the dripper in some part. In second irrigation management (PM), value of EC decreased which was mostly near the emitters (Fig. 5). As we can see in Fig. 6 the value of EC under PM+LR has not changed significantly. Accordingly we observed decrease in EC during development stage under PM irrigation management. Increase in irrigation amount under third irrigation management EC dose not change but increased the salt load in the soil. Before irrigation ( Day 97) After irrigation (day 98) Figure 4. Soil salinity under control management before and and after irrigation in development growth stage. 6

Before irrigation ( Day 97) After irrigation (day 98) Figure 5. Soil salinity under second irrigation management (PM) before and and after irrigation in development growth stage. Before irrigation ( Day 97) After irrigation (day 98) Figure.6. Soil salinity under third irrigation management (PM+LR) before and and after irrigation in development growth stage. 7

3.3. Irrigation depth, transpiration and irrigation volume Under first irrigation management (control) and during all plant growth stages the irrigation amount was not enough to cover irrigation water requirement (Fig. 7). Three times leaching was applied during the season which was 9 July, 4 August and 5 September 92 (respectively 101, 127 and 159 days after the first irrigation) where water depth in which does suddenly increased. To apply the water for leaching, one irrigation water saved and together with next irrigation water applied. Accordingly the amount of water applied to the farm were twice until leach out the salt out of the root zone area. In second Irrigation management (PM) In all cases, the irrigation depth shows slightly higher than irrigation water requirement because of the difference in the amount of 90% as water distribution uniformity (Eu). In third irrigation management (PM+LR) due to leaching a coefficient of 15%, in all cases the amount of gross water depth 15 percent more water applied compared to the PM. Pistachio evapotranspiration during the study year was about 9500 m 3 /ha during the measurement days while the total volume of water applied under control management was 6254 m 3 /ha and that was 9290 and 10682 for PM and PM+LR respectively 4. CONCLUSIONS Subsurface drip irrigation could be applied for saline irrigation water but irrigation water requirement must be estimated precisely. In the study farm trees were faced deficit irrigation during development growth stages in control management, but in other managements when evapotranspiration was estimated the soil water content in the root zone area were in the field capacity level and no deficit of water observed. Based on soil water content distribution in root zone area, emitter line distance of 1 m from the row of trees and 0.40 m under the soil surface were recognized appropriate to bring the proper wetted area into the soil. Soil salinity level in second management was less than that in third management. It was contributed to the more salt entrance by irrigation water into the soil under PM+LR. Where irrigation management was based on total of crop water requirement and leaching (PM+LR) soil salinity was about 12 ds/m within root zone area. SAR was less in PM compared to others irrigation managements. PM+LR bring better soil water content for root trees but was not effective to leach out the salinity. Sodium concentration in PM and PM+LR where less than that in control significantly. Mg concentration in control increased during the irrigation season but that was constant in PM+LR. Ca concentration in control was constant but decreased in PM and PM+LR. According to the results SDI is not able to leach out the accumulated salt from the root zone area but able to keep the salinity close to the salinity of irrigation water. A complementary irrigation water by surface irrigation or rainfall event is needed to leach out the salt from the soil at the end of irrigation season. 8

55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 181 187 193 199 205 211 mm/day 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 181 187 193 199 205 211 mm/day 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 181 187 193 199 205 211 mm/day 2 nd World Irrigation Forum (WIF2) 11 10 9 8 7 6 5 4 3 2 1 0 Control 11 10 9 8 7 6 5 4 3 2 1 0 PM 11 10 9 8 7 6 5 4 3 2 1 0 PM+LR Time after first irrigation (DAY) Figure 7. Irrigation depth in 2 days interval (Bars) and transpiration in different irrigation regims (control, PM, and PM+LR) 9

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