اﺛﺮ ﻋﻤﻖ ﻏﺮق آﺑﯽ ﺑﺮ ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ از ﺳﻄﻮح ﺷﺎﻟﯿﺰاري

The effect of submergence depth on evaporation losses in paddy fields

سابقه و هدف : در روش آبياري غرق آبي در اراضي شاليزاري ، تبخير آب ازسطح يكي از اجزاي تلفات آبﻣﺤﺴﻮبﻣﯽﮔﺮدد. ﻣﻘﺪار ﺗﺒﺨﯿﺮ در اﯾﻦ اراﺿﯽ ﺗﺎﺑﻊ ﻋﻮاﻣﻞ دﻣﺎ، رﻃﻮﺑﺖ ﻧﺴﺒﯽ ،سرعت باد ، سطح پوشش گياهي ، عمق ﻏﺮق آﺑﯽ، ﻋﻤﻖ اﯾﺴﺘﺎﺑﯽ در زﯾﺮ ﺳﻄﺢ ﺧﺎك و ﻋﻮاﻣﻞ ﻣﺘﻌﺪد دﯾﮕﺮ ﻣﯽﺑﺎﺷﺪ. در ﻣﺪﯾﺮﯾﺖﻫﺎي ﻣﺒﺘﻨﯽ ﺑﺮ آﺑﯿﺎري ﺗﻨﺎوﺑﯽ، ﺷﺎﻟﯿﺰارﻫﺎ از ﺣﺎﻟﺖ ﻏﺮقآب داﯾﻢ ﺧﺎرج ﮔﺮدﯾﺪه اﻧﺪ و در ﻫﺮ ﻧﻮﺑﺖ آﺑﯿﺎري ﺳﻄﺢ آب در آنﻫﺎ از ﺣﺪ ﻓﺎﺻﻞ ﻏﺮق آب ﺗﺎ ﻇﻬﻮر ﺗﺮك ﻣﻮﯾﯿﻦ ﺗﻐﯿﯿﺮ ﻣﯽﮐﻨﺪ .اﯾﻦ ﭘﮋوﻫﺶ ﺑﺎ ﻫﺪف اﻧﺪازه ﮔﯿﺮي ﻣﻘﺪار ﺗﺒﺨﯿﺮ در دوره رﺷﺪ ﺑﺮﻧﺞ در ﻋﻤﻖﻫﺎي ﻣﺨﺘﻠﻒ ﻏﺮق آﺑﯽ در ﺷﺮاﯾﻂ اراﺿﯽ ﺷﺎﻟﯿﺰاري اﺳﺘﺎن ﮔﯿﻼن در ﻣﺤﻞ ﻣﺰرﻋﻪ ﻣﺆﺳﺴﻪ ﺗﺤﻘﯿﻘﺎت ﺑﺮﻧﺞ ﮐﺸﻮر در ﻣﺠﺎورت اﯾﺴﺘﮕﺎه تحقيقات هواشناسي رشت در سال1392انجام شد. ﻣﻮاد و روش ها :ﭘﻨﺞ ﺗﯿﻤﺎر ﻣﺨﺘﻠﻒ ﺳﻄﺢ ﺛﺎﺑﺖ آب ﻧﺴﺒﺖ ﺑﻪ ﺳﻄﺢ ﺧﺎك ﺷﺎﻟﯿﺰار( 5، 2/5، 0 ، 5- ، 10- سانتيﻣﺘﺮ )در ﺳﻪ ﺗﮑﺮار و ﺑﺎ اﺳﺘﻔﺎده از ﻣﯿﻨﯽﻻﯾﺴﯿﻤﺘﺮ ﻧﺼﺐ ﺷﺪه در وﺳﻂ ﮐﺮت ﻫﺎي ﺑﺰرگ ﺷﺎﻟﯿﺰاري ﺑﺎ اﺳﺘﻔﺎده از ﻃﺮح ﺑﻠﻮك ﻫﺎي ﮐﺎﻣﻞ ﺗﺼﺎدﻓﯽ اﻋﻤﺎل ﮔﺮدﯾﺪ و ﺗﺒﺨﯿﺮ روزاﻧﻪ در آن ﻫﺎ اﻧﺪازهﮔﯿﺮي ﺷﺪ. ﯾﺎﻓﺘﻪ ها : ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ در ﻋﻤﻖﻫﺎي ﻣﺨﺘﻠﻒ ﻏﺮﻗﺎﺑﯽ در ﺳﻄﺢ 5% دربرخي موارد بايكديگر تفاوت ﻣﻌﻨﯽ دار دارﻧﺪ .ﺑﯿﺶ ﺗﺮﯾﻦ ﻣﻘﺪار ﺗﺒﺨﯿﺮ ﻣﺮﺑﻮط ﺑﻪ ﺗﯿﻤﺎر 10- سانتي متر ، به ترتيب معادل 120/8 و 94 ميلي متر بود.در ﻫﻤﻪ ﺗﯿﻤﺎرﻫﺎ ﺑﺎ ﮔﺬﺷﺖ زﻣﺎن از اﺑﺘﺪاي دوره، ﺗﺒﺨﯿﺮ در ﺷﺎﻟﯿﺰار ﺑﻪ ﻧﺼﻒﮐﺎﻫﺶ مي يابد . وﻗﻮع ﺑﺎرﻧﺪﮔﯽ نيز تبخير را تا 75% كاهش مي دهد. بدون در نظر گرفتن روزهاي بارندگي نيز تفاوت ﺗﺒﺨﯿﺮ در ﺳﻄﻮح ﻣﺨﺘﻠﻒ ﻏﺮﻗﺎﺑﯽ در ﺷﺎﻟﯿﺰار داراي ﺗﻔﺎوت ﻣﻌﻨﯽدار ﻣﯽﺑﺎﺷﻨﺪ. ﻣﻘﺎﯾﺴﻪ ﻣﯿﺎﻧﮕﯿﻦﻫﺎ ﻧﺸﺎن داد ﮐﻪ ﺑﺎﻻﺑﻮدن ارﺗﻔﺎع ﺳﻄﺢ ﻏﺮقآب در ﺷﺎﻟﯿﺰار ﻣﻮﺟﺐ اﻓﺰاﯾﺶ ﻣﯿﺰان ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ ﻣﯽﮔﺮدد .ﺑﺎ ﮐﺎﻫﺶ ﺳﻄﺢ ﻏﺮقآب و ﻧﺎزك ﺷﺪن ﻻﯾﻪ آب روي ﺧﺎك، ﺑﻪ ﺧﺼﻮص در دوره رﺷﺪ روﯾﺸﯽ، ﺗﺒﺨﯿﺮ ﮐﺎﻫﺶ ﻣﯽﯾﺎﺑﺪ .اﮔﺮ ارﺗﻔﺎع اﯾﻦ ﻻﯾﻪ ﺧﯿﻠﯽ ﮐﻢ ﺷﻮد و ﺑﻪ ﺻﻔﺮ ﺑﺮﺳﺪ و ﯾﺎ ﺧﺎك در ﺣﺎﻟﺖ ﻧﯿﻤﻪ اﺷﺒﺎع ﻗﺮار ﺑﮕﯿﺮد، ﺗﺒﺨﯿﺮ ﻣﺠﺪداً اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ .ﭘﺲ از آن در ﺷﺮاﯾﻄﯽ ﮐﻪ ﺳﻄﺢ آب درخاك پايين تر ازشرايط نيمه شرايط نيمه اشباع است ( 10- سانتي متر ) تبخير به طور معني داري كاهش مي يابد . ﻧﺘﯿﺠﻪ ﮔﯿﺮي: ﻧﺘﺎﯾﺞ اﻧﺪازهﮔﯿﺮيﻫﺎي ﺗﺒﺨﯿﺮ و ﻧﻮﺳﺎﻧﺎت آن ﺗﺸﺎﺑﻪ ﭼﺸﻤﮕﯿﺮي ﺑﺎ ﻧﻮﺳﺎﻧﺎت دﻣﺎي اﻧﺪازه ﮔﯿﺮي ﺷﺪه در ﻫﺮ تيمار ( در عمق 5 و 10 ﺳﺎﻧﺘﯽ متري در زير سطح خاك)و ﻫﻤﭽﻨﯿﻦ دﻣﺎي آب دارد و ﺗﯿﻤﺎرﻫﺎﯾﯽ ﮐﻪ داراي ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ ﺑﯿﺶ ﺗﺮ ﻫﺴﺘﻨﺪ، ﺗﯿﻤﺎرﻫﺎﯾﯽ ﻫﺴﺘﻨﺪ ﮐﻪ در ﺑﺎزه ﻫﺎي روزاﻧﻪ دﻣﺎﻫﺎي ﺑﯿﺶ ﺗﺮي در ﻣﺤﯿﻂ آب و ﺧﺎك آن ﻫﺎ ﺛﺒﺖ ﺷﺪه اﺳﺖ. در ﺷﺮاﯾﻂ وﺟﻮد آب ﮐﺎﻓﯽ وﺟﻮد ﻻﯾﻪ ﻧﻪ ﭼﻨﺪان ﺿﺨﯿﻢ ﻏﺮق اﻣﺎ در، آب ﺑﺎﻋﺚ ﺟﻠﻮﮔﯿﺮي از ﺑﺎﻻرﻓﺘﻦ ﺗﺒﺨﯿﺮ آب ﻣﯽﮔﺮدد، اما در صورت نبود آب لازم براي حفظ حالت غرق آب ،ﺑﺮاي ﮐﺎﻫﺶ ﺗﻠﻔﺎت ﺗﺒﺨﯿﺮ، استقرار آب در بيش از 5 سانتي مترﭘﺎﯾﯿﻦ ﺗﺮ از ﺳﻄﺢ ﺧﺎك در اوﻟﻮﯾﺖ ﻗﺮار دارد.

Background and Objective: Evaporation is one of the main components of water losses in submerged irrigation method in paddy fields. The amount of evaporation is a function of temperature, relative humidity, wind speed, vegetated surface, submerges depth, water table level and other elements. In different intermittent irrigation managements, paddy fields frequently are under submerged and non-submerged situation. In each irrigation practice, the water level changes from submerged to capillary crack. This research aims measuring of evaporation rate during rice growth in different submerged depths in Guilan Province paddy fields in Rice Research Institute near meteorological research station in 2013. Material and Methods: Five different water level treatments (5, 2.5, 0, -5, -10 cm) where applied to the farm in three repetition and using mini Lysimeters the evaporation is measured in daily scale in the middle of pig plots. Results: The results show that evaporation in different submerged levels is significantly different in 5%.The most and least evaporation amounts are consequently seen in 0 cm and 10 cm treatments respectively 120.8 and 94 millimeters. In all treatments the evaporation reduces during the time to the half. Precipitation minimize also evaporation rate till 75%. Neglecting precipitation dates also does not change the difference between treatments. The comparisons show that higher levels of water on the soil surface cause higher evaporation losses. By reducing water level and narrowing water depth on soil surface, especially in vegetation period evaporation reduces. If the thickness of this layer reduces and reaches to zero or soil became semi saturated, evaporation increases again. If the thickness of this layer reduces and reaches to zero or soil became semi saturated evaporation increases again. Then when the soil became dryer and the water level stays at -10 cm below soil level, the evaporation decreases significantly. Conclusion: The results of evaporation measurements and its fluctuations are highly strongly to fluctuations of soil temperature in every treatment (in depth of 5 and 10) and water temperature and treatments which have higher records of temperature in the soil and water environment, have severer evaporation rates. In case of enough available water, presence a thin layer of water on top soil surface can reduce effectively evaporation. But in the absence of water necessary to maintain submergence, to reduce evaporation losses it is recommended to keep water level table in lower than 5 cm from top soil surface.