Page 51 - soil-plant-water relationship and water requirement
P. 51
SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT
5.3 EFFECTIVE RAINFALL
The primary source of water for agricultural production for most of the world is rainfall.
Three main characteristics of rainfall are its amount, frequency and intensity, the values
of which vary from place to place, day to day, month to month and also year to year.
Information of the amount, intensity and distribution of monthly or annual rainfall for
the most important places in the world is generally available. Long-term records of daily
rainfall have been compiled for years
In its simplest sense, effective rainfall means useful or utilizable rainfall. Rainfall is not
necessarily useful or desirable at the time, rate or amount in which it is received. Some
of it may be unavoidably wasted while some may even be destructive. Just as total
rainfall varies, so does the amount of effective rainfall.
Effective Rainfall means the precipitation for plant consumption use or the rain
that provide benefits to the plant to achieve the consumptive used
Effective rainfall controlled by the following parameters:
Amount, Intensity, time, duration and frequency
Original soil moisture condition
Peak needed condition
Type of plant and stage of growth.
Type of irrigation
Field water storage condition
5.4 FIELD WATER BALANCE
Field Water Balance means that we take into account all quantities of water aspects
such as loss, exchange and storage of water within a given volume of soil in a
given period of time in a farm.
A water balance can be established for any area of earth’s surface by calculating the
total precipitation input and the total of various outputs.
The purpose of water balance is to describe the various ways in which the water supply
is extended
Knowledge in Field Water Balance is needed to assess the appropriate methods for
reducing water losses and maximizing water use (utilization of water) where it is an
important factor in agricultural production.
From an agricultural point of view, it is generally most appropriate to consider the water
balance of the crop root zone. In its simple form, the equation reads.
42
