Page 37 - soil-plant-water relationship and water requirement
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SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT
3.3 SOIL WATER AND PLANT USE
Plants do not have access to all of the available moisture. The roots can breathe more
readily when the soil moisture is close to field capacity, as opposed to when the soil
moisture is approaching the wilting point.
Irrigation is used to keep the moisture content of the soil at the proper level for optimal
growth. When the soil has dried to a specific point, such as 70% of the field capacity,
one approach to determine when to water is when the soil has dried to a certain point.
Figure 3.3-1: Rate of Crop Growth Curve
3.4 SOIL MOISTURE MEASURING METHOD
3.4.1 By Feel
This is by far the easiest method. Assessment by feel is good for experienced
people who have sort of calibrated their hands. The type of soil is important.
3.4.2 Gravimetric Method
This is equal to:
P = M = Mass of Water
m
w
MS Mass of Dry Solids
o
Weigh wet soil in a container, put in oven at 105 C for about 24 - 48 hours;
weigh again and obtain the weight of water by subtraction. A good soil should
have moisture contents between 50% and 60% and for peat or organic soils, it
can be greater than 100%.
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