Soil Moisture Measurements with the Neutron Method Supplement Weighing Lysimeters

Abstract

Evaluation of soil moisture changes with the neutron method agreed closely with that obtained from the weighing lysimeters. Evapotranspiration can be determined with either method by the equation ET = P ‐ G ‐ Q ± Δ M where ET = evapotranspiration, P = precipitation, G = percolation, Q = surface runoff and ΔM = change in soil moisture. Differences were shown in the soil moisture extraction pattern under deep‐rooted and shallow‐rooted meadow crops. The hydrologic implications of this difference are discussed.

Determination of Evapotranspiration Using the Neutron Scattering Method

“…depth. The top \'vas cut off 4 in. above the soil surface and a small cone of soil was pressed against.the tube at the surface, to prevent water from running down the outside of the tube.…”

Comparison of Lysimeter and Neutron Scatter Techniques for Measuring Evapotranspiration from Semiarid Rangelands

“…The neutron scatter method has been used successfully to determine ET from lysimeters under irrigation and subhumid conditions (McGuinness et al, 1961;Bowman and King, 1965;Harrold and Dreibelbis, 1967;and Van Bavel and Stirk, 1967). This paper discusses the utility of the neutron scatter method for ET determinations on semiarid rangeland and compares results with those obtained from small hydraulic lysimeters.…”

“…Supplementation with other techniques for measuring water in the soil surface would improve the neutron method. McGuinness et al (1961) used resistance blocks to determine soil water in the top 18 cm of soil. With proper technique and special calibration curves, the neutron method can be improved for water measurements near the soil surface (Van Ravel and Stirk, 1967;Black and Mitchell, 1968;and Luebs et al, 1968).…”