|Al-Qinna, Mohammed -|
|Scott, H.DON(DECEASED) -|
|Brye, Kristopher -|
|Brahana, John -|
|Sharpley, Andrew -|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 28, 2014
Publication Date: N/A
Interpretive Summary: Soils that form from weathering rocks can contain a lot of rock fragments. These rocks can have a strong effect on soil properties. Often, soils with a lot of rocks are poor for agricultural uses. They tend to be low in nutrients and don't hold water very well for plant growth. In this study, the soils of a small watershed in the Ozark Highlands of northwestern Arkansas were intensively studied to try to relate soil physical properties to their ability to transmit water from rainfall. Soil samples were collected for analysis, and water movement into surface soil layers was measured in the field. The results indicated that soils at different positions in the watershed had very different properties and these differences could be related to the soil forming processes at each position. The amount of rocks affected how much pore space in the soil was available to transmit water. Soils with high rock contents could transmit a lot of water but may not hold very much for plant uptake. The presence of rocks in soils with a lot of clay or silt can also result in lower water flow rates as the water must flow around the rocks. The results of this study are important to scientists and growers interested in understanding and managing soil water content and movement in soils with high amounts of rock fragments.
Technical Abstract: This paper investigates the effect of rock fragments on soil physical hydraulic properties within the mantled karst landscapes of the Savoy Experimental Watershed (SEW), a setting typical of much of the Ozark Plateaus. Water resources in these settings are highly susceptible to contamination. As a result, land-management practices can become a critical source of non-point contamination if not managed properly. Three soil series were investigated in Basin 1 of the SEW; Captina cherty silt loam, Clarksville cherty silt loam, and Razort gravelly silt loam. The soils were classified, sampled, and physically investigated for gravel content, total and soil bulk density, total and soil porosity, soil particle distribution, and total carbon (C) and nitrogen (N) content. Also, ponded infiltration and intake rates were measured using double-ring and single-ring infiltrometers. Results showed that the distribution in the profile of gravel percentage by weight and depth followed a nonlinear relation. The variability in soil-gravel content was attributed to variations in underlying lithology and weathering. The Razort soil had the highest gravel content, ranging between 15% at the surface and 80% at 1.0 m depth, and this strongly affected the soil physical behavior. Gravel content had a linear effect on reducing the soil fractional bulk density. Total porosity decreased with depth to an average of 20% by volume for all soils, whereas the soil porosity increased with depth to an average of 10% by volume. Statistical analysis indicated that soil bulk density was related to the total C content, and this effect reverses the effect of gravel on total bulk density. According to ponded infiltration and intake measurements, the rock fragments reduce the cross-sectional area available for water to flow, increase the tortuousity, and reduce the hydraulic conductivity of the soil system. Using the parameter fitting of the experimental data to Philip’s equation, the sorptivity was independent of gravel content, and the transmissivity was 30 times greater in Razort compared to Captina and Clarksville soils. Saturated hydraulic conductivity calculated using Kutilek’s approach indicated that increasing rock fragments in the Razort soil enhanced the hydraulic conductivity to 252 mm h-1.