Investigation of the effects of water suspended load on soil hydraulic characteristics in different soil textures

Background and Objectives
Infiltration rate is the rate at which water enters into the soil. It affects the water supply needed for plants and the recharge of groundwater. This soil hydraulic properties can be affected by the soil physicochemical characteristics such as particle size distribution, organic matter, structure and porosity, and management practices (grazing, traffic, tillage etc.). Along with, the rate of water infiltration into the soil can be affected by water characteristics such as hydraulic head and concentration of muddy water. Deposition of suspended load in the soil’s pores blocks the soil pathways for water movement. In various studies that had been done in the flood spreading areas, the researchers have found that soil hydraulic characteristics varies remarkably after flood spreading. Although there is a lot of information on the effects of flood spreading on the soil infiltration rate, little information is available on the effects of concentration of muddy water on water infiltration process. Therefore, this study was conducted to determine effects of different concentrations of muddy water on the soil hydraulic characteristics in different soil textures.

Materials and Methods
A field study was designed in three areas with different soil textures (sandy loam, silt loam and clay loam) with six concentrations of muddy water consist of zero (clear water), 10, 100, 1000, 10000 and 100000 mg lit-1. Water infiltration rate was measured using small rings with 32-cm in diameter in eighteen points of each land (six treatments at three replications) with 2-m intervals. In total, fifty four field experiments were done using the ring infiltrometer in three areas. Initial infiltration rate and final infiltration rate was calculated for each muddy water concentration using the loss of water head (cm) per unit of time during infiltration process (hours). Soil samples were taken from soil surface (0-30 cm depth) and various physicochemical properties consist of particle size distribution, bulk density, organic matter content and structure stability were determined in the lab. The analysis of variance was done for determining independent effects of two factors (soil type and muddy water concentration) and their interactions on the initial and final infiltration rate using the Tukey’s test. Statistical significant level was considered to be more than 95% (p< 0.05).

Results and Discussion
Based on the results, the highest initial and final infiltration rate of the soils occurred at zero muddy water concentration (clear water). The highest initial infiltration rate and final infiltration rate was in sandy loam (91.2 cm h-1 and .6 cm h-1, respectively), while the lowest values were observed in clay loam (58.8 cm h-1 and 5.7 cm h-1, respectively). A large difference was among the soils in final infiltration rate (35 %) as compared with initial infiltration rate (11 %). Higher infiltration rate of sandy loam under muddy water concentration is associated with higher macrospore percentage as well as hydraulic conductivity. Initial infiltration rate under muddy water concentrations was significantly affected by soil texture (p< 0.001), muddy water concentration (p< 0.001) and their interaction (p< 0.01). Initial infiltration rate in the soils decreased considerably with increasing muddy water concentration in all soils. The lowest effect of muddy water concentration was in sandy loam, while the highest difference was observed in clay loam. There was no similar decreasing trend in initial infiltration rate with increasing muddy water concentration in the soils. This result showed that there is significant interaction between soil type and muddy water concentration in initial infiltration rate. A large decline in initial infiltration rate (20%) in sandy loam was at 1000 mg lit-1 muddy water concentration, whereas the loss of initial infiltration rate in clay loam was at 100 mg lit-1 muddy water concentration (55%). Also, significant differences were found in final infiltration rate in the soil textures (p< 0.001) and muddy water concentration (p< 0.01). Nevertheless, there wasn’t significant interaction between the two factors in final infiltration rate. A large decline in final infiltration rate in sandy loam and clay loam was at 10000 mg lit-1 muddy water concentration (27%) and 100 mg lit-1 (26%), respectively.

Conclusion
The results indicated that soil hydraulic characteristics (initial and final infiltration rate) are significantly affected by both soil texture and muddy water concentration. Soil type is an important factor determining the effect of muddy water concentration on initial infiltration rate, while the effect of muddy water concentration on final infiltration rate in all soils is relatively similar. This study revealed that effect of muddy water concentration on the loss of initial water infiltration rate is more than final infiltration rate. Initial infiltration rate in a fine textured soil such clay loam is more susceptible to muddy water concentration as compared to a coarse textured soil (sandy loam). This research showed that the flood spreading to recharge of groundwater in fine-textured soils is limited and is only possible at very lower muddy water concentration.