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One of the most simple methods of measuring soil moisture is by using a tensiometer. A tensiometer consists of a sealed hollow tube filled with water, a porous tip and a vacuum gauge. In dry soil, water is drawn out of the tensiometer, reducing the internal water volume and creating a partial vacuum which registers on the gauge - the drier the soil, the higher the vacuum and hence the gauge reading. Watering - whether from rain or irrigation - reverses this action and the internal vacuum now draws water back into the tensiometer and the gauge reading goes down. Once the field capacity of a particular soil is known, an irrigation schedule can be initiated which prevents soil moisture reaching 'wilting point' one the one hand and on the other hand prevent field capacity being exceeded and valuable moisture being lost through drainage. A tensiometer is an invaluable irrigation tool. |
