Assume the A horizon of the soil from the soil from the bulk density measurement
ID: 155117 • Letter: A
Question
Assume the A horizon of the soil from the soil from the bulk density measurement has the following additional properties:
thickness = 28 cm 0g (theta g) (field capacity) = 0.32 0g (theta g) (permanent wilting) = 0.10
(I dont know how to insert the theta symbol so I put 0 instead)
1. Calculate how many cm of available water it can provide if the water content at sampling is 26% (0g (theta g) = 0.26).
2. From the result in part 1, calculate how many days a corn plant can survive without rainfall or irrigation if it requires 0.80 cm of water per day at its current growth stage and its root can exploit the full volume of the A horizon.
3. Calculate how many inches of rain would be required to bring the A horizon to field capacity from its current water content.
Any help would be greatly appreciated and please include all steps and numbers if you can, thank you!
Explanation / Answer
Field capacity is the water content of the soil two to three days after a rain or irrigation event when the remainder of water has been removed by the downward forces of gravity. This value of field capacity assumes that the water removed from the soil profile is only removed by gravity, not through the plants or through evaporation. Field capacity is not the same as saturation. When the soil is saturated, all the spaces between the soil particles are filled with water. When the soil is at field capacity, the spaces between the soil particles contain both air and water.
The permanent wilting occurs when the volumetric water content is too low for the plant to remove water from the soil. About half of the water in the soil at field capacity is held too tightly to be accessible to plants. The soil is considered to be at permanent wilting point when the water potential in the soil is at or below -1.5 MPa, so the permanent wilting point is the water content of the soil at -1.5 MPa water potential.
Soil at permanent wilting point is not dry. When the water content of a soil is below the permanent wilting point, water is still be present in the soil, but plants are unable to access it.
Available water (if water content at sampling is 26 %) = 28 X 0.32 = 8.96 cm x 0.26 = 2.33 cm - 0.1 = 2.23 cm
No. of days a corn plant can survive without rainfall or irrigation, if it requires 0.80 cm water per day = 2.23 / 0.80
= 2.79 days
Inches of rain required to bring A horizon to field capacity from its current water content = 8.96 cm = 3.53 inch