جستجوی مقالات مرتبط با کلیدواژه « layered soil » در نشریات گروه « آب و خاک »

The pattern of root distribution in layered soils is one of the significant issues in the calculations of soil water and irrigation management and planning. The objective of this study was to determine the pattern of root distribution of soybean in layered soils and its effect on water uptake. The research was conducted in a completely randomized design with 15 treatments consisting of three different textures of soil (light, heavy, and medium) in four replications. The pattern of root distribution was monitored by the sampling of columns at the end of the growth period of the soybean. It was observed that the presence of the layer with medium texture has led to better plant development and growth after comparing the treatments in terms of plant growth. In general, root length density decreased with increasing soil depth, except in cases where there were different layers of soil, and root length density takes place in the following order: root length density in layers with medium texture≥ heavy texture≥ light texture. The rate of root water uptake rate was highest in the sandy layers, intermediate in clay, and lowest in loamy texture. Also, the rate of root water uptake rate increased significantly with increasing depth regardless of treatments. It can be concluded that the pattern of root distribution and plant growth is significantly affected by soil texture and its stratification.

Hydraulic conductivity is one of the important physical properties of the soil used extensively in water and soil science. Most of the soil processes take place in unsaturated soil conditions. This study was conducted in order to evaluate the effect of soil layering and water table on saturated and unsaturated hydraulic parameters using a tension disc in five suction heads, i.e. 0, 5, 10, 15, and 20 cm. The experimental tests were done on three same samples with 56 cm diameter and 85 cm height in three compacted layers with soil bulk densities of 1.18, 1.38 and 1.68 gr.cm-3 and water table depths of 85 (no water table) 50, and 25 cm. Additionally, we considered a one-layered sample to investigate the effect of bulk density. The experimental results showed that soil layering caused changes in the values ​​of saturated and unsaturated hydraulic conductivity. Also, sensitivity of the saturated hydraulic conductivity to soil layering was more than that of the inverse air entry suction(α). Compared with the treatment with no water table, the saturated hydraulic conductivity of the layered soil in treatments with water table depths of 25 cm and 50 cm decreased by 52 % and 27.6 %, respectively.

In heterogeneous and layered soils, in order to a better management and description of chemicals movement on such media, perception of solute movement is very important. In this study, the effect of soil layers arrangement with different thicknesses on solute movement was investigated. For this purpose, two soils with different textures (i.e. loamy sand and clay loam) were used to prepare six two-layered columns (two 10cmcolumns, two 20cm-columns and two 30cm-columns), and the movement of sodium chloride in these columns was tested. First arrangement, namely the loamy sand layer was beneath the clay loam layer, was compared to second arrangement (the layers were swapped), and it was observed that the solute breakthrough and the appearance of peak concentration in the bottom of column were faster and the tail of breakthrough curve was shorter. By increasing the thickness of layers, the differences also increased, so that by swapping the two layers in 5 cm-layers, the difference between the times that breakthrough solute reaches to an almost constant concentration, the time of maximum concentration appearance and the duration of breakthrough curve tail time were 210, 250 and 40 minutes, respectively. Layers arrangement more than column length effected the solute movement, so that the peak concentration in second arrangement of 10cm-column was 40 min later than the first arrangement of 20cm-column and, the concentration in second arrangement of 20cm column was 100 min later than the first arrangement of 30cm-column. The solute movement was simulated by finite element method using the GeoStudio model. The simulation results have coefficient of determination (R2) more than 0.984 and root mean square error (RMSE) less than 0.530 g/L. This means that the simulation results were satisfactory.