Soil moisture measurement Techniques

Question 1

What is are the direct methods of soil moisture content measurement

Answer 1

The gravimetric or thermogravimetric method

Using your hands to feel the soil

Question 2

Explain the gravimetric method

Answer 2

This is the use of a weighing scale and an oven to check the moisture content. A fresh soil sample is taken to the lab and it is weighed , and then it is put in an oven to dry at 105degrees for 24hours . Then the dry weight of the moisture is taken . The different between the fresh weight and the moist weight is the moisture content of the soil.

Question 3

What is the formula for the gravimetric moisture content

Answer 3

Gravimetric formula = ( wet soil weighed - dry soil weighed / dry soil weighed ) * 100

Question 4

What are the advantages of gravimetric method of measurement

Answer 4

1. It is the most direct and reliable method
2. The equipments used are simple and not expensive
3. It doesn’t require a level of expertise , so it can be used by local farmers
   4.It does not have radiation harzards
4. The core sampler used to collect the soil sample, can also be used to calculate for bulk density

Question 5

What are the disadvantages of gravimetric method

Answer 5

It is time consuming and laborious
Getting soil samples in stony areas is difficult
If there is crop cover with established roots, sampling may hamper crop growth
It involves destructive sampling, so sampling cannot be done in the same place twice.

Question 6

What is the formua for converting gravimetric moisture content to volumetric moisture content

Answer 6

Gravimetric moisture content* Bulk density

Question 7

What is the formula for volumetric moisture content

Answer 7

volume of water/bulk volume of the soil ie (mass of water/density of water)/bulk volume of the soil

Question 8

What is the neutron scattering technique

Answer 8

This technique uses the amount of Hydrogen present.Hydrogen can be found in water. The amount of hydrogen is directly proportional to the scattering of neutrons when the equipment is being used. Neutrons usually scatter at a fast rate in a dry soil, so if a soil is moist and has a lot of hydrogen present through H20, the hydrogen in the water slows down the neutrons.

Question 9

State some advantages of using neutron scattering technique

Answer 9

1. You can take a large moisture content reading in a short time
2. It is portable so multiple moisture content readings can be taken at the same time
3. Destructive sampling doesn’t occur, as long as the access tube is placed in the soil moisture content can be checked at different depth
   4.Once the instrument is calibrated , taking the readings is straight forward
4. It gives you a direct volumetric moisture content measurement.

Question 10

Explain the Gamma ray technique

Question 11

Explain the electrical resitance method

Question 12

State advantages and disadvantages of the electrical resistance method

Question 13

What is the tensiometry method