Depth Of Soil Column Research Articles

Field experiments to study evaporation from a saturated bare soil

A field experiment to measure evaporation from a bare sandy soil, starting from saturation, has been carried out at the Lido beach of Venice during summer-autumn 1997. A large tank embedded in the sand of the Lido beach, was filled with the same sand. Time Domain Reflectometry (TDR) probes were, buried at different depths in the tank to measure the soil water content. Water was then poured in the tank to reach saturation. The measurements were taken from June 26 up to the end of November. Water content was automatically measured at 5, 10, 15, 20, 25, 35, 45 cm depths at two hours time steps. The temporal behaviour of the water content is characterised by successive drying intervals separated, by precipitation events that sometimes were able to restore the water content almost to the initial (saturated) value. Furthermore a very small diurnal cycle is recognisable in the water content behaviour at all depths. All the levels show to be involved in evaporation, reducing their water content as the experiment goes on in spite of precipitation and decrease in solar radiation. Using soil water content profiles and precipitation, the water budget, that is the total water evaporated, is evaluated. The cumulative evaporation, computed on the whole soil column depth, shows a time behaviour that can be separated in two different stages. The first stage is well described by a linear function of time and corresponds to a daily mean evaporation of 4.6 mm. The second stage results are approximated by a square root of time. The analytical solution of the diffusion equation, found for the second drying stage using an initial condition derived from the experimental data, allows an estimation of the mean hydraulic diffusivity of the sand.

Influence of Drying Period on Migration Behavior of Radionuclides in Aerated Soil Layer

In an aerated soil layer under natural condition, water that infiltrates into it flows discontinuously because of repeated cycles of rainfall and drying. Therefore, column tests, in which 2,000 mi of deionized water was fed into sandy soil layer dried for 3~90 days after it is contaminated by 60Co, 85Sr and 137Cs aqueous solution, were carried out to examine influence of the drying period on migration behavior of those nuclides. All the radionuclides showed both a steeply decreasing part corresponding to their cationic form and a gradually decreasing part corresponding to their particulate form in the concentration distribution curve along the soil column depth. In the vicinity of the top surface of soil layer, no influence of drying on 60Co and 137Cs concentrations was observed, but S5Sr moved a little into a deeper part from the top surface with longer drying period. Such moving tendency of 8ESr was found to be connected with the Ca2+ concentration in the interstitial water. In the deeper soil layer, no influence of drying on 85Sr concentration was observed, but the 60Co and 137Cs concentrations were increased with the drying period. This is considered to be caused from that each product of the movable 60Co(OH)2 and the 131Cs adsorbed on the fine particle increased with the rise of pH and the fine particle concentration, respectively, during the drying period. Thus, this study has suggested possible causes affecting on the radionuclide migration under discontinuous flow condition.

Influence of drying period on migration behavior of radionuclides in aerated soil layer.

In an aerated soil layer under natural condition, water that infiltrates into it flows discontinuously because of repeated cycles of rainfall and drying. Therefore, column tests, in which 2,000 mi of deionized water was fed into sandy soil layer dried for 3~90 days after it is contaminated by 60Co, 85Sr and 137Cs aqueous solution, were carried out to examine influence of the drying period on migration behavior of those nuclides. All the radionuclides showed both a steeply decreasing part corresponding to their cationic form and a gradually decreasing part corresponding to their particulate form in the concentration distribution curve along the soil column depth. In the vicinity of the top surface of soil layer, no influence of drying on 60Co and 137Cs concentrations was observed, but S5Sr moved a little into a deeper part from the top surface with longer drying period. Such moving tendency of 8ESr was found to be connected with the Ca2+ concentration in the interstitial water. In the deeper soil layer, no influence of drying on 85Sr concentration was observed, but the 60Co and 137Cs concentrations were increased with the drying period. This is considered to be caused from that each product of the movable 60Co(OH)2 and the 131Cs adsorbed on the fine particle increased with the rise of pH and the fine particle concentration, respectively, during the drying period. Thus, this study has suggested possible causes affecting on the radionuclide migration under discontinuous flow condition.

Hydraulic conductivity and leaching of an organic saline-sodic soil

The hydraulic conductivity of an organic saline-sodic soil was measured as a function of the organic matter content, dry material, pH, total iron oxides, clay content and optical density of the leachate in a soil column. Also, changes in sodium concentration of the percolating water along the soil column were recorded. The data showed that plugging of pores by dispersed organic and clay particles was the main reason of reduced hydraulic conductivity, while dissolution of organic substances was the major cause for increased hydraulic conductivity. Salt concentration increased with soil column depth first in an exponential and later in a double linear relationship until an almost steady state appeared in the whole soil column.

The Effect of Soil Conditioners on Water Movement through Lateritic Sandy Loam Soil

AbstractThe lateritic sandy loam soil of Gopali suffers by a high infiltration rate and percolation loss. The investigated soil was treated by four soil conditioners, CMC, PVA. Guargum and Lignosulphonate (LIG.) at 0.05 per cent and 0.10 per cent concentration level. The infiltration of water at −2 m bar pressure in horizontal column of soil was studied. The experimental results indicate that the lignosulphonate has increased the time by 30% and 70% to penetrate the 15 cm depth of soil column at 0.05 and 0.10 per cent concentration level, respectively. In the case of PVA, increase of time was 18 per cent and 33 percent at these the concentration level. Guargum at high concentration level increased the time by 31 per cent to penetrate the same depth of soil. Whereas CMC at high concentration reduced the time by 8 per cent. Similar trends were found in case of volume of water penetration and infiltration rate of treated soil.

Movement and distribution pattern of the residues of granular insecticides in tropical soil and okra plants

The increased downward mobility of phorate, quinalphos and carbofuran residues was detected in soil with increase in depth of soil column whereas aldicarb was found to remain localised mainly in 0–7.5 cm and 7.5–15.0 cm layers. Persistence of organophosphate insecticides was higher as compared to carbamates in all the soil layers. Residues of all the four insecticides got distributed in all parts of okra plant through uptake but accumulated in higher amounts in fruits only.