Page 22 - soil-plant-water relationship and water requirement

SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT

2.3 INFILTRATION PROCESS

Infiltration is the movement of water vertically from the surface into the soil.

2.3.1 Infiltration Terminologies

Infiltration Rate (mm/h)

The rate at which a particular soil is able to absorb rainfall or irrigation
It is related to the saturated hydraulic conductivity of near surface soil

Cumulative Infiltration (mm)

Accumulated depth of water infiltrating during given time period

Infiltration Capacity (mm/hr)

Maximum rate at which water can enter a soil in a given condition.
If the precipitation rate exceeds the infiltration capacity, runoff will usually
occur

Basic Infiltration Rate(mm/hr)

Infiltration capacity declines rapidly during the early part of a storm and then
tends to constant value, which is referred to as basic infiltration rate.

2.3.2 Factors Affecting Infiltration Rate

Precipitation: The amount and characteristics (intensity, duration, etc.) of
precipitation that falls as rain or snow are the most important factors
controlling infiltration. Because precipitation that seeps into the ground over
time seeps into streambeds, a stream will often continue to flow even if it
hasn't rained in a long time and there is no direct runoff from recent
precipitation.

Soil characteristics and hydraulic conductivity: Some soils, such as clays,
absorb less water at a slower rate than sandy soils. Soils absorbing less water
result in more runoff overland into streams.

Soil saturation and temperature: Like a wet sponge, soil already saturated
from previous rainfall can't absorb much more, thus more rainfall will become
surface runoff.

Land cover: Some land uses have a significant impact on rainfall runoff and
infiltration. Runoff can be slowed by vegetation, giving it more time to
penetrate into the earth. Impervious surfaces such as parking lots, roads, and
developments operate as a "speed lane" for rainfall, channelling it directly into

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