Which of the following statements regarding soil moisture measurement devices is/are TRUE? (Variation QB_PARAMETRIC_IDE_SWP_024)
Options:
(A) Tensiometers operate accurately only within a tension range of $0$ to $0.8\text{ bar}$ ($0$ to $80\text{ kPa}$)
(B) Gypsum electrical resistance blocks are more suitable for measuring matric suction in the drier range ($1$ to $15\text{ bars}$)
(C) Time Domain Reflectometry (TDR) measures soil moisture by determining the apparent dielectric permittivity of the bulk soil
(D) Neutron probe scattering measures hydrogen ion concentration and is completely unaffected by organic matter or salinity
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Tensiometers cavitate and break the water meniscus above $0.8\text{ bar}$ (A is true).
2. Gypsum blocks have fine pore matrices suited for dry range $1-15\text{ bars}$ (B is true).
3. TDR measures the high dielectric constant of water ($\approx 80$) vs soil solids ($\approx 3-5$) (C is true).
4. Neutron probes thermalize fast neutrons via collision with all hydrogen atoms, including organic matter, boron, and chlorine; calibration is sensitive to organic matter (D is false).