Characterization of the conditions that exist in the feedlot surface and soil profile is important to evaluation of the potentials for soil and water pollution. Cattle action and management activities create a dynamic condition in the feedlot. The organic matter surface causes physical and biochemical changes in the soil that are unlike natural or cultivated soils. The feedlot profile can be described as three layers: the organic matter, the interface, and the underlying soil. Measurable characteristics include bulk density, infiltration, and content of organic matter, water, and nitrate‐N. Generally, the surface 15.2‐cm depth of feedlot soils is compacted and has a high bulk density. Infiltration into the feedlot surface layers is essentially zero. There is no transpiration, and the soilwater content is more uniform through the profile than on cropped land.

No abstract

Infiltration, water stability of soil aggregates, and water retention characteristics were measured on a Sharpsburg silty clay loam (Typic Argiudolls) in a 4‐year cropping sequence. The cropping systems include soybean (Glycine max L. Merr.), sorghum (Sorghum bicolor L. Moench), corn (Zea mays L.), and fallow, in various sequential cropping combinations.The influence of cropping systems on size distribution of water‐stable aggregates is indicated by the values of geometric mean diameter (GMD). The rank order of GMD for the soybean sequences was: soybean after fallow > soybean after sorghum > soybean after corn > continuous soybean. The low GMD of continuous soybean reflected the negative effect of soybean roots in building a stable soil structure. Cumulative infiltration after 4 hours of water application was 6, 13, 29, and 41 cm for continuous soybean, sorghum after soybean, fallow after soybean, and corn after sorghum, respectively. The low infiltration was associated with low macroporosity and decreased aggregate stability. Both Kostiakov's and Philip's equations fitted the infiltration data reasonably well statistically, but Kostiakov's equation was a better fit for the early and late stages of infiltration.

Differences in traffic and tillage intensity among positions in ridge tillage create distinctly different environments for microbial activity. This study was conducted to assess the impact of long-term controlled wheel traffic on soil respiration in ridge-till and to use correlation analysis to identify relationships between soil respiration and soil physical and chemical properties. Soil respiration was evaluated from 0 to 30 cm in one row, one tractor-trafficked interrow, and one nontrafficked interrow of continuous corn (Zea mays L.) and continuous soybean [Glycine max (L.) Merr.]. Soil respiration was measured on disturbed samples at three levels of water-filled pore space (WFPS) by gas chromatography for 25 d. Properties assessed included bulk density, soil strength, texture, aggregate-size distribution, saturated hydraulic conductivity (/Cat), water retention characteristics, organic C, and total N. Soil respiration was greatest at 0 to 7.5 cm in each position and decreased significantly below that depth. Correlation analysis indicated microbial activity in-ridge-till varied spatially in relation to changes in the soil physical environment. Soil respiration was negatively correlated with bulk density at each WFPS. The K sn was positively correlated with soil respiration at 0 to 7.5 cm for each WFPS. Under drier soil conditions, as exemplified by 47% WFPS, aggregates <1.0 mm and gravitational water were positively correlated with soil respiration at the 0 to 7.5 cm. Soil environments characterized by bulk density <1.4 Mg m" 3 and £* >10 cm h" 1 were associated with respiration rates >4 and 12 mg COj-C L"' soil d~', respectively.