جستجوی مقالات مرتبط با کلیدواژه "loam" در نشریات گروه "آب و خاک"

Sustainable agriculture at arid and semi-arid areas depends on optimized usage of fresh water resources. Evaporation from soil surface and deep percolation categorized as unuseful losses at irrigation, so their reduction could increase the root water uptake efficiency and yield production. Subsurface drip irrigation could provide this situation. Proper depth for installing dripper is the place that reduces soil surface evaporation and deep percolation. The objective of this study was to investigate the effects of various dripper installation depth on soil water content distribution and root water uptake and to choose the proper depth. For this purpose, HYDRUS-2D software was used to investigate the effect of three factors on non-beneficial losses and consumed water in drip irrigation, numerically. These factors were soil texture (loam, clay loam and sandy loam), installation depth (0, 10, 15 and 20 Cm) and dripper discharge (1, 2, 4 and 8 l.h-1). The results showed, although increasing the installation depth could reduce cumulative evaporation up to 40%, but the best installation depth was 15 Cm with discharge rate of 1 l.h-1, according to the amount of deep percolation and consumed water. The effect of soil texture was more than the effect of installation depth on the amount of irrigation water, so that the amount of irrigation water in 2 l.h-1 discharge rate was 2.9, 3.1 and 4.6 m3.m-1 for loam, clay loam and sandy loam soil texture, respectively. Also, for clay loam texture, dripper discharge had the highest effect on root water uptake and the installation depth had the lowest effect on soil surface evaporation.

The relation between water table depth and evaporation rate from bare soil is of great importance in arid and semi-arid areas. In this region, due to over irrigation, the water table is very close to the ground surface which leads to salinization of the soil. Evaporation from soil columns in the presence of a water table is a important that has received great attention for many decades. The soil-drying process has been observed to occur in three recognizable stages. The first stage is evaporation with constant intensity. Secondly, evaporation is in descending order. The third stage is the residual evaporation of low intensity, which begins after excessive drying of the surface layer of the soil and its effect on reducing the hydraulic conductivity of the soil. Precise determination of evaporation from bare ground surface in semi-arid or arid regions then becomes critically important. The purpose of this study was to determine the effect of water table depth on the evaporation from soil surface, as well as the determination of different evaporation stages.

The soil used in this experiment was loam with a bulk density of 1.32 gr/cm3. The experiment was conducted in a greenhouse and the duration was 74 days. Soils Were sived through a 2-mm mesh and then packed into the soil columns using soil funnel. The soil columns were cylindrical PVC tubes of 200 mm inside diameter. Water table was stabilized at depths of 400, 600 and 800 mm from the soil surface, and the experiment was repeated twice. For stabilizing the water table in different depths, Each soil columns contained a pipe from the botton, to supply water from bottles that maintained the water table constant. The water losses from the soil profile was measured at different depths and times using Delta-T Device Moisture Meter.

The results showed that water content between 0 and 160 mm in the soil column were decrease during the experiment and close the water table depth remained saturated. In the steady-state, the rate of water loss from bottle next to the soil column is equal to the rate of evaporation from the soil surface. In a non steady-state, the rate of evaporation equals the sum of the rate of water loss from bottle and the water depleted from the soil profile. The maximum evaporation from the the water table was related to a depth of 400 mm and equal 384.6 mm and the highest water loss from the soil profile was related to a depth of 800 mm and equal 51.3 mm. By increasing the water table depth from 400 to 800 mm (increased 100%), the evaporation rate from the water table 24 percent and the total evaporation from the soil surface decreased by 16.5 percent. The length of the first stage of the evaporation for the water table depth 400 mm was 2 days and for 800 mm less than 1 day.

The results of this study gave us information on the flow of water above the shallow water table. Water content changes in the soil surface soil are higher than close watertable. Movement of water close water table is liquid and close the soil surface is vapor. The duration of the first stage of evaporation has decreased with increase water table depth. In general, it can be concluded that evaporation from the water table can provide a large portion of the water requirement by the plants.

Salinity and organic matter deficiency are the main problems of soils in arid and semi-arid regions. The use of residues in presence of salinity may affect soil properties differently. In this research, the effect of zero, 1. 5%, 3%, and 4. 5% application of pistachio residues and electrical conductivity (salinity) of water including three levels of 4, 8, and 12 dS m-1 were investigated on water repellency of soils with three different textures, namely, silty clay, loamy, and loamy sand. The static and dynamic water repellencies were determined by measuring soil-water contact angle and water penetration time. The mean values of soil-water contact angle for clay, loam, and sandy loam soils were 70±2. 5º, 65±2. 6º, and 62 ±3. 4º, and water droplet times (WDPT) were about 35±2. 6, 26±1. 6, and 18±0. 6 s, respectively. Accordingly, static water repellency of the fine textured soil was more than that of the medium and coarse textured soils by 3% and 7%, respectively, while the dynamic water repellency was 24% and 95% more, respectively. Salinity had no significant effect on static or dynamic water repellency. However, the salinity of 12 dS. m-1 increased the static water repellency of clay soil by 7%. The residues increased the static and dynamic water repellency of soils, except in silty clay soil where the effect of residues on static water repellency was not significant. In general, salinity levels had no significant effect on the mean values of the static and dynamic water repellency of soils; whereas application of residues (except for 4. 5% residues) increased both static and dynamic water repellency. Furthermore, since the applied residues were probably not fully decomposed in the time period used in this study, it is recommended that longer or different time periods be used in the future studies.