Surface liming effects on soil radiation attenuation properties

Abstract

This study investigates the effects of surface liming on soil attenuation radiation properties. For this, measurements of soil chemical attributes (pH, organic carbon, H+Al, Al3+, Ca2+, and Mg2+) and attenuation radiation parameters (mass attenuation coefficient, μm, atomic and electronic cross sections, σa and σe, effective atomic number and electron density, Zeff and Nel) were carried out. This aim was motivated by the fact that possible μm variation might cause as well variation in the determination of soil physical properties. The studied soil, classified as a Dystrudept sity-clay, is located in South Brazil. The trial consisted of five stripes, one of them under pasture and the remaining under no-till system (NTS). Lime rates of 0, 10, 15, and 20 t ha−1 were broadcast on the NTS soil surface. Disturbed soil samples were collected 30 months after liming at the top (0–10 cm) and subsoil (10–20 cm) layers. Soil chemical attributes were characterized following standard experimental procedures. The soil oxide composition, obtained by EDXRF analysis, was used to calculate μm for 241Am and 137Cs photon energies with XCOM computer code. μm values were employed to calculate σa, σe, Zeff, and Nel and to predict variations in soil bulk density (ρ) and total porosity (φ). Surface liming notably increased contents of soil pH, Ca2+, and Mg2+ while reduced H+Al and Al3+ at the top soil layer, where μm, σa, σe, and Zeff were also increased with the lime rates. However, at the subsoil layer, liming neither lessened soil acidity nor induced remarkable changes in the attenuation parameters. When using 137Cs photon energy, incoherent scattering totally dominated over the radiation interaction processes whereas photoelectric absorption and coherent scattering substantially contributed when 241Am photon energy was used. Therefore, the increasing in soil attenuation parameters at the top soil layer was more accentuated considering 241Am than 137Cs photon energy. Variation in μm caused considerable variation in ρ and φ only for 241Am photon energy. The findings regarding the effect of μm variation induced by liming on the determination of soil physical properties are extremely relevant because traditionally, in the soil science area, μm values are calculated without considering any chemical modification to which the soil can be submitted. Bearing in mind that ρ and φ are important parameters from the agricultural and environmental points of view, not representative measurements of μm can lead to biased values of ρ and φ.