Irrigations in Sandy Soil Regions that Utilize Brackish Water
Grant-in-Aid for Developmental Scientific Research
|Allocation Type||Single-year Grants |
|Research Institution||Tokyo University of Agriculture (1984-1985)|
Iwate University (1983)
SUGI Jiro (1984-1985) 東京農業大学, 公・私立大付置, 研究員 (20078231)
原 道宏 (1983) 岩手大学, 農学部, 助教授
|Project Period (FY)
1983 – 1985
Completed (Fiscal Year 1985)
|Budget Amount *help
¥8,500,000 (Direct Cost: ¥8,500,000)
Fiscal Year 1985: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1984: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1983: ¥6,300,000 (Direct Cost: ¥6,300,000)
|Keywords||Saline Soil / Salt Accumulation / Disconnection of Cappilarity / Irrigation by Temperature Differences / Distillation / Vinyl-house / 圧入式地下かんがい|
In the tropics, one year is generally devided into two halves; wet and dry seasons. Severe shortage of irrigation water is commonly observed in the dry season.
If we could get sufficient amount of irrigation water then agricultural production could be done even in the dry season because the other conditions as the degree of temperature and the amount of solar radiation are all satisfied already in the tropics.
A few million hectares of sandy salt-affected soil are distributed in the inland region of Thailand(North East Thailand). There, salt crusts are formed on top of the soil surface in the dry season and the land becomes unsuitable for agricultural use. This is one of the most typical examples of the phenomena in the dry season. Even in this kind of dry land, very often, we find rather shallow(usually 1m to 2m deep) under ground water, which quantity is large. However, the quality of the water is usually very low because high concentration of salt(ex. 1% NaCl) is contained in it, thus
the water is brackish. Brackish water is, of course, unsuitable for irrigation because of its high concentration of salt.
On the other hand, in fine days of the dry season, there are prenty of solar radiation in the day time and it becomes cooler in the night. So, there is a fair chance to obtain good quality of water by distilling the brackish water using the solar energy and the temperature diference.
The distillation system, however, should not be expensive but should be appropriate for the agricultural use. In this range, some trials of the distillation of water have been carried out using simple small vinyl houses. As a result, 1 to 2 liters/ <m^2> of high quality(10 ppm=0.001% of salt concentration) water were obtained in a day from brackish under-ground water which contained about 1%of salt and located at the depth of 1.5m from the ground level. Therefore, this method is suitable in obtaining fair amount of good quality water from brackish water in the tropics.
It has long been said that if soil is separated from under ground water by a horizontal air gap then the vapor movement in the air gap will show unidirectionality(upward); when water is warmer than soil, vapor moves from water to soil easily because the air gap has instability of density distribution. However, when soil is warmer than water, vapor will not move so easily because the air in the gap will be stable in the distribution of air density.
Corresponding to this supposition, an experimental apparatus has been made and the idea has been tested. Under the conditions that water and soil temperatures are 30 ゜C and 20 ゜C, respectively, about 0.3mm/day of distillation has been observed. Although this amount is a little bit smaller than the theoretical value, it does not contradict each other considering the other accompanying conditions. Therefore, using a horizontal air gap, salt accumulation can be avoided and good quality water is obtained at the lowest part of the overlying soil layer. But the quantity of thus obtained water is much smaller than vinyl house method.
An idea of "Subirrigation by pressurized injection of water into soil" has been newly presented in order to use the smallest amount of good quality water most efficiently in the dry season. The relationship between the applied water pressure and the volume of injected water has been obtained numerically to use it in the future application of the new idea. Less
Report (1 results)
Research Products (6 results)