Soil Moisture Percentage

Introduction to Measuring Soil Moisture Percentage

Soil Moisture is the amount of moisture present in the soil. It can be estimated by feel and the appearance of the soil. To estimate soil moisture, Tensiometers or resistance blocks may be used. For the measurement of moisture, we check it in at least one location for each area of the field because it differs from other areas in soil slope and texture.

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Methods for Measuring Soil Moisture Percentage

There are mainly three methods for measuring soil moisture percentage.

Soil Survey Standard Test Method: This method is based on the removal of soil moisture by oven drying a soil sample until the weight remains constant.
Time-Domain Reflectometer: This method involves the propagation of electromagnetic waves or signals. This method is independent of soil texture, temperature and salinity. It is possible to perform long term in situ measurements. But the disadvantage of this method is that it is very costly.
Gravimetric method: This method involves removal of the soil sample from the field, and determination of the mass of water contained in the soil relative to the mass of dry soil. This method ensures accurate measurements but it has lot of disadvantages. This is time consuming method, inapplicable to automatic control.

Soil Moisture Percentage : Equipment Used

Tape measures, permanent marking pen, soil auger instruments, box of gallon sized Zip-lock plastic bags, field note book, access to a soil lab etc.

For fine grained soils, medium grained and course grained soils, procedures are different.

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Soil Moisture Percentage :Calculation


In general, Soil moisture is reported as percent moisture, where

Moisture content (%) = ((wet weight – dry weight)/(wet weight)) * 100

We calculate the moisture content of the soil as a percentage of the dry soil weight.

MC% = (W2 – W3)/ (W3-W1) * 100

Where:

W1 = Weight of Tin (g)

W2 = Weight of moist soil + tin (g)

W3 = Weight of dried soil + tin (g)

Where chemical analysis are performed on moist samples because it is convenient to correct the results to an oven-dry basis by use of appropriate Moisture Factor (MF) which is calculated as follows:

MF = (W2 –W1)/(W3 – W1)

Or     MF = 1 + (MC/100)

Here MC = Moisture Content