Spectrophotometric Determination of Soil Water Content

Abstract

The absorbance at 1.94µ by a soil‐methanol extract was used for measuring the soil water contents of three different textured soils. A linear relation between absorbance and soil water content was adequate for moisture determinations ranging from air dry to the moisture equivalent. For Quincy loamy sand and Barnes loam soils, calibration based only on laboratory standards was sufficient. For Houston Black clay, calibration against oven‐dry samples was necessary. Determination time was approximately 1 hour.

Bidirectional reflectance of bare soil surfaces in the visible and near‐infrared range

“…The second is rather analytic and is based on the study of the physical processes, which explain the phenomenon of reflection (Jacquemout et al, 1991). The first relationships have been presented by Bowers and Smith (1972) from measurements taken on kaolinite samples, sifted at different sizes. They showed a decreasing relationship between particle size and reflectance.…”

Influence of several size properties on soil surface reflectance

“…The refl ectance of soils, measured under laboratory conditions on samples with their disturbed surfaces, increases with a decrease of the soil particle size (Orlov, 1969;Bowers & Smith, Brought to you by | MIT Libraries Authenticated Download Date | 5/12/18 3:38 AM 1972). Bowers & Hanks (1965), testing the refl ectance of soil materials of the texture from coarse clay to sand, found that the character of this relationship is exponential.…”

“…Along with the increase of soil moisture from oven-dry soil to the hygroscopic capacity, the spectra levels do not change (Tolchelnikov, 1974;Cierniewski, 1985) or it drops a little (Vinogradov, 1983). With a further increase in water content to the fi eld capacity, the spectra levels decrease sharply, in proportion to the increase in the water content in the soil (Bowers & Smith, 1972;Tolchelnikov, 1974;Vinogradov, 1983). A further increase in soil water content to full saturation does not bring about any change in spectra levels (Tolchelnikov, 1974;Vinogradov, 1983) or causes their slight increase (Białousz et al, 1978;Cierniewski, 1985Cierniewski, , 1993Music & Pelletier, 1986).…”

Soil Water Measurement with an Inexpensive Spectrophotometer

“…Absorbance was then calculated by Eq. [1] above. In addition, 12 other important agricultural soils were selected and two water contents randomly assigned to each; the maximum assigned water content was 48%.…”