بررسي تجربي و عددي توزيع رطوبت خاك در آبياري قطره اي زير سطحي در خاك‌هاي لايه‌اي مسطح و شيب دار

Experimental and Numerical Investigations of Soil Water Distribution under Subsurface Drip Irrigation in Level and Sloping Layered Soils

در پژوهش حاضر الگوي توزيع رطوبت خاك تحت آبياري با قطره ­چكان­ هاي زير سطحي در خاك د­و ­لايه و در دو حالت زمين مسطح و شيب­دار از طريق انجام آزمايش­هاي مزرعه­اي بررسي و اثرات شرايط شيب زمين و لايه­اي بودن خاك به­طور منفرد و توام بر الگوي خيس­شدگي خاك بررسي شد. مقايسه­ ها بين نيمرخ ­هاي رطوبتي مشاهداتي در خاك­هاي مسطح و شيب­دار، بيان­گر اين موضوع بود كه با افزايش مدت آبياري نيمرخ رطوبتي ايجاد شده در خاك­هاي شيب­دار با نيمرخ حاصل در خاك­هاي مسطح تطابق بيشتري مي­يابد. نتايج گوياي اين موضوع بود كه با افزايش مدت پخش آب اثر غير همسان بودن خاك كاهش پيدا مي­كند. به­دليل بالا بودن هدايت هيدروليكي لايه پاييني، با رسيدن رطوبت به مرز لايه­ها جبهه رطوبتي داراي شكست گرديده، گسترش رطوبت در جهت عمودي بيشتر شده و شكل پياز رطوبتي به ­صورت بيضي بود. از نرم ­افزار هايدروس دو بعدي براي شبيه ­سازي جبهه رطوبتي براي شرايط مشابه با آزمايش­هاي صحرائي استفاده شد. ﺪ. ﺑﻪﻣﻨﻈﻮر ﺑﺮآورد دﻗﺖ ﻧﺮماﻓﺰار، ﻓﺎﺻﻠﻪ ﺷﻌﺎﻋﯽ ﺟﺒﻬﻪ رﻃﻮﺑﺘﯽ ﻣﺸﺎﻫﺪاﺗﯽ و ﺷﺒﯿﻪﺳﺎزي ﺷﺪه از ﻣﺤﻞ ﻗﻄﺮهﭼﮑﺎن در زاوﯾﻪﻫﺎي ﻣﺨﺘﻠﻒ ﻣﻮرد ﻣﻘﺎﯾﺴﻪ ﻗﺮار ﮔﺮﻓﺖ. ﺑﺮ اﯾﻦ اﺳﺎس ﻣﻌﯿﺎرﻫﺎي ﺟﺬر ﻣﯿﺎﻧﮕﯿﻦ ﻣﺮﺑﻌﺎت ﺧﻄﺎ 2/47 ﺳﺎﻧﺘﯽﻣﺘﺮ، ﺿﺮﯾﺐ ﻫﻤﺒﺴﺘﮕﯽ 0/82 و ﺿﺮﯾﺐ ﮐﺎرآﯾﯽ ﻣﺪل 0/24 ﺣﺎﺻﻞ ﮔﺮدﯾﺪ. ﻣﻌﯿﺎرﻫﺎي ﻣﺬﮐﻮر در ﺧﺎك دو ﻻﯾﻪاي ﺷﯿﺐ دار ﻧﯿﺰ ﺑﻪﺗﺮﺗﯿﺐ ﺑﺮاﺑﺮ 4/03 ﺳﺎﻧﺘﯽﻣﺘﺮ، 0/75 و 0/36 ﻣﺤﺎﺳﺒﻪ ﺷﺪ. در ﮐﻞ اﯾﻦ ﻧﺘﺎﯾﺞ ﻗﺎﺑﻠﯿﺖ ﺧﻮب ﻧﺮماﻓﺰار ﻫﺎﯾﺪروس در ﺷﺒﯿﻪﺳﺎزي ﺣﺮﮐﺖ آب در ﺷﺮاﯾﻂ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﺗﺎﯾﯿﺪ ﻧﻤﻮد

In this research the wetting pattern of soil under subsurface drip irrigation was investigated through field experiments on two layered soil at the level and sloping lands, and the interaction and individual effects of the sloping and layered soil conditions on the wetting pattern were studied. Comparisons between observed soil moisture profiles in the level and sloping soils clarified that by increasing the application duration, the wetting patterns of the sloping soil showed more adaptation with that of the level soil. The results indicated that the effect of soil anisotropy was declined with increasing the water application duration. Due to high hydraulic conductivity value of the sublayer soil, the wetting front showed an inflection after reaching to the boundary of the two layers, so that the vertical expansion of pattern was increased and the wetting bulb transformed to an ellipse. The HYDRUS 2D software was applied to simulate the wetting patterns at the same conditions of filed experiments. The radial distance of the soil wetting fronts in the different angles from emitters were compared with corresponding simulations in order to evaluate the model accuracy. Results showed that HYDRUS simulations had a good agreement with observed data with Root Mean Squared Error (RMSE) value of 2.47 cm, correlation coefficient (r) value of 0.82 and model Coefficient of Efficiency (CE) value of 0.24 for the layered level soil. Also the values of these statistical criteria for sloping layered soil in the same order were 4.03 cm, 0.75 and 0.36 respectively. Generally, these results confirmed reliable ability of HYDRUS software for simulation of water movement in the studied conditions.