Surface liming effects on soil radiation attenuation properties

Purpose

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, μ_m, atomic and electronic cross sections, σ_a and σ_e, effective atomic number and electron density, Z_eff and N_el) were carried out. This aim was motivated by the fact that possible μ_m variation might cause as well variation in the determination of soil physical properties.

Materials and methods

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 μ_m for ²⁴¹Am and ¹³⁷Cs photon energies with XCOM computer code. μ_m values were employed to calculate σ_a, σ_e, Z_eff, and N_el and to predict variations in soil bulk density (ρ) and total porosity (φ).

Results and discussion

Surface liming notably increased contents of soil pH, Ca²⁺, and Mg²⁺ while reduced H+Al and Al³⁺ at the top soil layer, where μ_m, σ_a, σ_e, and Z_eff 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 μ_m caused considerable variation in ρ and φ only for ²⁴¹Am photon energy.

Conclusions

The findings regarding the effect of μ_m variation induced by liming on the determination of soil physical properties are extremely relevant because traditionally, in the soil science area, μ_m 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 μ_m can lead to biased values of ρ and φ.

     

Performance of a photo‐heterotrophic,hypersaline system for intensive cultivation of white leg shrimp (Litopenaeus vannamei) with minimal water replacement in lined ponds using a stochastic approach

The aim of the study was to evaluate the performance of Litopenaeus vannamei in an intensive photo‐heterotrophic hypersaline system with minimal seawater replacement, and establish relationships between parameters of a stochastic production model and relevant water quality variables. Six experimental 1000 m² lined ponds were stocked at a density of 120 shrimp m^?2 for a 105‐day trial. Salinity increased from 37 to 45 ± 2 g/L, and the water level was maintained with the weekly addition of filtered seawater, equivalent to 1.6% per day. The stochastic model predicted that, at harvest, there is 95% confidence that the system produces between 12.1 and 14.7 t/ha with a mean final individual weight of 13.1 g and a mean survival of 84.2%. Sensitivity analyses showed that dissolved oxygen and individual final weight of shrimp were the main variables influencing yield variance. Nitrogenous compounds were maintained between optimal cultivation levels (NH₃–NH₄⁺ = 0.73 ± 0.43 mg/L, N–NO₂^? = 0.09 ± 0.05 mg/L, N–NO₃^? = 3.22 ± 0.11 mg/L). Heterotrophic bacteria (6.6 ± 3.4 × 10⁵ CFU/ml) and chlorophyll‐α concentration (108.5 ± 80.2 μg/L) showed a similar development pattern, indicating a strong relationship between bacteria and microalgae during cultivation. Vibrio spp. concentrations were low (1.24 ± 1.42 × 10³ CFU/ml). It was shown that the photo‐heterotrophic system could be used in hypersaline conditions, typical of semi‐arid regions, to consistently produce between 12.1 and 14.7 t/ha in 15 weeks.