Field determination of the LARA for the Water Balance
The LARA depends on the water retention characteristics of the soil and the permissible depletion factor (AG) from which the plant cannot take enough moisture and its development begins to be affected.
In the cultivation of sugarcane, a value of 40 to 60% is generally established as an allowable depletion of usable water in the soil before applying irrigation. This water is what is known as quickly usable water sheet (LARA):
LARA = AG x THE A
Where AG is the allowable depletion (in%) of the total usable water and LAA is the usable water sheet (mm).
To start the water balance you can use the values presented in the LARA reference table of the main soils of the Cauca river valley, although LARA should be determined preferably in the field using the following methodology: