Soil science depart -MNSUAm

1. DETERMINATION OF SOIL MOISTURE CONTENTS

2. Moisture contents of the soil is determined by using various
methods as;
• Gravimetric method/Oven dry method
• Tensiometer method
• Neutron Probe method
• Gypsum block method/ Resistance block
• Touch & feel method
• Sun drying method

3. GRAVIMETRIC METHOD/OVEN DRY METHOD
• Soil sample is taken from the field by using screw auger.
• The sample is transferred to an aluminum or stainless steel
soil sample container.
• The weight of the sample container along with soil sample is
noted.
• Then it is placed in a hot air oven for 24 h at 105 oC.
• The dry weight of the soil sample along with container is again
weighted

4. Fresh weight of the soil sample with container = W1 (g)
Oven dry weight of soil sample with container = W2 (g)
Empty weight of the container = W3 (g)
Moisture content of the soil on dry weight basis as calculated as;
Moisture content (%) = (W1 - W2)/(W2 - W3) × 100

5. TENSIOMETER METHOD
• Bore the soil with the help of auger with sharp cutting edge
• Insert the Tensiometer into the access hole and cover the
porous cup with the soil.
• After few hours, a tension is produced due to concentration
gradient and water molecules moves from porous cup to the
soil.
• Plot the readings on a paper against the days.
• At equilibrium stage, water present in the soil is equal to
water present in the cup.

6. NEUTRON PROBE METHOD
• The access tube is inserted into the soil by drilling a hole with
the help of an auger.
• It is few centimeters above the soil and converted with an
inverted case.
• The neutron probe is inserted into the access tube by
carefully lowering down cable to the desired depth.
• Then the counting rates are determined.
• Initially the probe is to be adjusted and calibrated against
volumetric determination of soil moisture content.

7. GYPSUM BLOCK METHOD/RESISTANCE BLOCK
• Make a hole in the field with an auger to a desired depth.
• Place it inside and fill back the bore in small depth by placing
the soil.
• Two electrodes are embedded in the block. The upper end of
the electrode is connected with wire, which in turn connected
with the resistance meter.
• Block is filled with the water. If the moisture present more in
the block then it tends to flow out when equilibrium is
reached. If moisture is more in the soil then resistance will be
high.
• After passing the current through the gypsum block, if the
resistance of the conductance is more, means more moisture
is present in the soil and hence the conductance will be low.

8. TOUCH & FEEL METHOD
• In this method, when small amount of soil is kept in hand and
ball formation takes place by pressing the soil with fingers and
also the scars of fingers are formed on the ball it means
moisture is present in the soil.

9. SUN DRYING METHOD
• In this method, a plastic sheet is taken and weight it i.e. W1
• Place the soil sample on it and weight it again i.e. W2
• Keep the soil sample under sun drying and weight it when
sample is favorable after 7 h during cool while after 5 h in hot
season i.e. W3
• The moisture content in soil sample is determined as;
Moisture (%) = (W3 – W1) / (W2 – W1) × 100