LESSON 1;Determination of Irrigation Schedules Flashcards
The process of determining when to irrigate and how much water to apply based upon measurements or estimates of soil moisture or water used by the plant.
Irrigation scheduling
A measure of the adsorptive forces by which soil retains water. Tension is a measure of negative pressure (suction) relative to the prevailing atmospheric gauge pressure of zero.
Tension
Unit commonly used in irrigation scheduling to express soil-water tension.
Bar
The soil-water content after the force of gravity has drained or removed all the
water it can, usually 1 to 3 days after rainfall. Field capacity is considered the
upper limit of plant-available water. When measured under field conditions it
is equivalent to a soil-water tension of approximately 0.1 bar
Field Capacity (FC)
Water in the soil that is free to drain or move by the force of gravity.Gravitational water is the volume of water in the soil between saturation and
field capacity. This water is not usually used by plants.
Gravitational Water
Water retained in soil pores after gravitational water has drained or that is
held loosely around soil particles by surface tension. Most of the soil-water
available to plants is capillary water, but not all capillary water is available to
plants.
Capillary Water
The soil-water content at which healthy plants can no longer extract water from the soil fast enough to recover from wilting. The permanent wilting point
is considered the lower limit of plant-available water. At this point, the soil-water tension is considered to be 15 bars.
Permanent Wilting Point (PWP)
The amount of water held in the soil that is available to plants; the difference
between field capacity and the permanent wilting point.
Plant-Available Water (PAW)
Water in thin, tightly held films around soil particles; not available to plants.
Unavailable Water
The amount of plant-available water removed from the soil by plants and evaporation from the soil surface.
Depletion Volume
Accurately measures soil
moisture content by weighing soil samples before
and after drying, but its slow process limits its
usefulness for irrigation scheduling, especially in
sandy soils that dry quickly.
Gravimetric Method
Measures soil water suction using a sealed, water-filled tube with a porous tip and a
vacuum gauge.
Tensiometer
Commonly known as
gypsum blocks due to their material composition,
utilize the principle of water conductivity to
measure soil moisture.
Electrical Resistance Blocks
Similar to colorimeters, use filters to isolate specific wavelengths of light for measuring
ion concentrations.
Photometer
Play a crucial role in irrigation
scheduling by providing farmers with a clear
overview of their financial resources and
expenses related to irrigation activities.
Budget Sheet
