Subtopic: Measurement of infiltration, soil moisture and irrigation water infiltration
Question Statement:
An undisturbed soil sample is collected from a field with a core cylinder having an internal diameter of 60 mm and length of 100 mm. The weights of moist soil and oven dried soil are 0.48 kg and 0.44 kg respectively. Assuming density of water as 1000 kg·m⁻³, the water depth (in metres per metre depth of soil) is ________ (Rounded off to two decimal places)
Official Answer Key:
0.12 to 0.16
Step-by-Step Solution & Explanation
Step 1 — volume of the core (= bulk volume of soil):
V = (π/4)d²L = (π/4)(0.060)²(0.100) = 2.827 × 10⁻⁴ m³
Step 2 — mass and volume of water:
Mass of water = 0.48 − 0.44 = 0.04 kg
Volume of water = 0.04/1000 = 4.0 × 10⁻⁵ m³
Step 3 — volumetric moisture content:
θᵥ = volume of water/bulk volume = (4.0 × 10⁻⁵)/(2.827 × 10⁻⁴) = 0.1415
Step 4 — equivalent water depth. The depth of water stored in a soil depth D is d = θᵥ × D. For D = 1 m:
d = 0.14 m per metre depth of soil
Alternative route: bulk density ρ_b = 0.44/2.827 × 10⁻⁴ = 1556 kg·m⁻³; gravimetric moisture (dry basis) = 0.04/0.44 = 9.09%; θᵥ = 0.0909 × 1556/1000 = 0.1415 — same result.
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