Agricultural Uses
The water content is the water lost from a soil or a
fertilizer sample when it is dried at 105°C to a constant
weight. It is expressed either in terms of mass of water
per unit mass of soil or as the volume of water per unit
apparent volume of the soil or the fertilizer.
The water content in a plant is not static because there
is a continuous process of intake from, and loss to, the
surrounding environment.
The amount of water in a soil directly affects the
growth of crops, microbes and soil organisms. The
strength of the soil, which determines the root
penetration and the energy requirements for tillage,
depends on the water content.
Direct or indirect measurements of soil water are
necessary, for which there are many techniques
available. Some methods do not require taking a soil
sample to a laboratory. These include the electrical
resistance method, neutron probe method, tensiometer
method and soil psychrometer technique. These methods
are used regularly and are quicker to use than the
gravimetric method for rapid and frequent estimations of
soil water content.
Water conductivity diminishes sharply as the water
content decreases, because more pores are empty and
unavailable for water flow. The sharp decline in
conductivity with decreasing soil water content has two
important consequences, namely, that it limits drainage
loss, and the loss by evaporation and transpiration. The
water that is briefly held in the soil due to a very high
water content, is hardly of any use for plant growth.
Unless the profile or the substratum has some impeding
layers to stop drainage, surplus water drains out of the
pedon within a few days.
