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Determination of Soil Moisture at Low Tension by Constant Head Technique.

Dr. M. H. Ali
SSO
BINA

H.N. Turral
Research Fellow
The Uni. of Melbourne

Abstract/ Executive Summary:

The relationship between the amount of water and tension under which the water is held by the soil throughout the entire range gives a good deal of insight into the physical properties of soil. In this study, a device, called ‘Constant-head apparatus’ was constructed to determine soil moisture at low tension. The technique was applied to determine soil moisture retention at 100 cm and 250 cm suction. The device controls the suction head precisely. It was found to be accurate and easy to operate.

Keywords: Moisture characteristics curve, Constant-head apparatus, Low tension

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Program Area: Crop-Soil-Water Management

Commodity: , Land management

Objectives:

To determine soil moisture release curve using hanging column technique for 0.05 to 0.3 bar.

Methodology:

This is a simplified procedure adapted from Stakman et al.(1969) to determine moisture retention at low suction (100 cm & 250 cm). A small capacity pump (fish pump) was sealed within a glass-walled box and only the intake & exhaust openings were open outside through small tube. This allows generation of suction pressure at low heads to suck water from the target soil sample through the intake tube; and the hanging column maintained required suction head. The flux serves as a water collector as well as suction distributor. To determine moisture retention at different suctions; the samples were saturated in a saturated sand box equilibrated at 4 cm suction, covered with nylon cloth; and then weighed.. A layer of kaolin slurry (1-3 mm thick) was spread over the nylon cloth and the samples were placed on the plate (1 bar). The air tubes were set for 100 cm water. The pump was then started. After 2 days, when the samples equilibrated with tension, the slurry was removed & the samples were weighed. The process was repeated for 250 cm suction.

Source of Information: Bangladesh J. Agri. Engg. 12(1&2): 63-68, (2001)

Article Link (Online Journal):

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Achievement/Findings:

Moisture release gradient at low tension provisioned by hanging column technique is unique and has practical implications for crop water management. Water content at 100 cm was found relativity high, about 42%.

Knowledge Management: Journal