Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2005
Publication Date: 5/1/2005
Citation: Iqbal, J., Thomasson, J.A., Jenkins, J.N., Owens, P.R., Whisler, F.D. 2005. Spatial variability analysis of soil physical properties of alluvial soils. Soil Science Society of America Journal. 69:1338-1350. Interpretive Summary: Efficient soil-water management in irrigated agriculture involves minimizing water inputs and optimizing the crop yield potential, which often requires understanding of soil-water-landscape interactions. In addition, knowledge of water movement in agricultural soils is important to irrigation scheduling, land drainage, nutrient transport, runoff pollution, and ground water contamination. The saturated hydraulic conductivity of soil(KSat) is an important physical property that influences the capacity of the soil to retain and transport water. This study determined the spatial variability of KSat, soil texture and bulk density in a 162-ha field of upland cotton, and used geostatistical methods to determine the positional similarity of these measured soil properties. Semivariogram models for most variables indicated moderate to strong spatial dependence beyond the original sampling distance of 91 meters. However, Ksat values were not normally distributed, and the semivariogram had high nugget (375 cm day-1) and sill (1574 cm day-1) values, and low range (70 m). To reduce nugget effects on KSat, a shorter sampling scale might be adopted for fields in the Mississippi Delta region. Kriged contour maps of soil physical properties indicated bulk density had a moderate to strong positional similarity with percent sand, percent clay, and plant available water content. Comparatively high bulk density in B1 horizons suggests sub-soiling might be needed to improve soil infiltration and drainage of water.
Technical Abstract: Little is known of spatial variability and relationships among different soils and soil physical properties in intensely tilled agricultural fields. This present study determined variability of soils in a 162-ha field and used geostatistical methods to compare the positional similarities among different soil properties. The field was sampled on a ~91 m grid consisting of 209, 1-m deep soil profiles at three depths based on soil horizon. Spatial analysis indicated high variability across the field for soil texture, bulk density (BD), water retention, and saturated hydraulic conductivity (KSat). Semivariogram models for most variables indicated moderate to strong spatial dependence beyond the original sampling distance and relatively low nugget and sill values. Because semivariograms for KSat had high nugget (375 cm day-1) and sill (1574 cm day-1), and low range (70 m), a shorter sampling scale might be adopted to reduce KSat nugget effects. Kriged contour maps indicated BD had moderate to strong positional similarities with sand, clay, plant available water content, and water content at 33 and 1500 kPa pressure heads. The correlation coefficient between BD and water content showed a decreasing trend with increasing pressure head, suggesting low influence of BD at higher pressure heads at each depth. Comparatively higher average BD values in the B1 horizon than the Ap and B2 horizons suggests sub-soiling would enhance water infiltration rate.