Rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes. Six experiments were conducted on two soils and a uniform sand using three experimental methodologies. The results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills. Velocity did not vary with slope, and Reynolds number was not a consistent predictor of hydraulic friction. This result was due to interactions of slope gradient, flow rate, erosion, and the formation of rill roughness, bed structures, and head cuts. A relationship for rill flow velocities was proposed. Stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set, while other hydraulic variables were not. The data for stream power and sediment load fit the form of a logistic curve (r 2 = 0.93), which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory.

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The surface soil organic C (SOC) concentration is a useful soil The dark color of soil is typically associated with high property to map soils, interpret soil properties, and guide fertilizer organic-matter concentration and high native fertility. and agricultural chemical applications. The objective of this study was Soils with thick, dark surface horizons are often sepato determine whether surface SOC concentrations could be predicted from remotely sensed imagery (an aerial photograph of bare surface rated from other soils at the highest categorical level in soil) of a 115-ha field located in Crisp County, Georgia. The surface many soil classification systems, reflecting the differ-SOC concentrations were determined for soil samples taken at 28 ences in the genesis of soils as well as the importance field locations. The statistical relationship between surface SOC conof these soils as a medium for plant growth and indepencentrations and image intensity values in the red, green, and blue dent natural bodies worthy of further study (Schulze bands was fit to a to a logarithm linear equation (R 2 ϭ 0.93). The et al., 1993). Research has been done concerning the distribution of the surface SOC concentrations was predicted with relationships between soil color and soil organic matter. two approaches. The first approach was to apply the relationship However, many of these studies were based on Munsell to individual pixels and then determine the distribution; the second color notations for specific soils at specific locations approach was to classify the image and then apply the relationship (Alexander, 1969; Steinhardt and Franzmeier, 1979; to determine the class boundaries and means. Eight levels of surface SOC concentrations were classified in both approaches, and there Schulze et al., 1993) or for the purpose of designing was good agreement between the two approaches with a probability spectral sensors (Pitts et al., 1983; Griffis, 1985; Smith value near one using a paired t-test. The predicted and measured et al., 1987). surface SOC concentrations, based on additional soil samples from There were attempts to quantify relationships be-31 field locations, were compared using linear regression (r 2 ϭ 0.97 tween soil color and organic matter concentrations by and r 2 ϭ 0.98 for the two approaches). The surface SOC concentrations Brown and O'Neal in the 1920's (Schulze et al., 1993). were correctly classified in 77.4 and 74.2% of cases for the two ap-Later, color charts or tables that described the relationproaches. The procedures tested were accurate enough to be used ships between soil color and organic-matter concentrafor precision farming applications in agricultural fields.

Application of broiler (Gallus gallus domesticus) litter to grasslands can increase ammonium (NH4-N) and dissolved reactive phosphorus (DRP) concentrations in surface runoff, but it is not known for how long after a broiler litter application that these concentrations remain elevated. This long-term study was conducted to measure NH4-N and DRP in surface runoff from grasslands fertilized with broiler litter. Six 0.75-ha, fescue (Festuca arundinacea Schreb.-)bermudagrass [Cynodon dactylon (L.) Pers.] paddocks received broiler litter applications in the spring and fall of 1995-1996 and only inorganic fertilizer N in the spring of 1997-1998. Surface runoff from each paddock was measured and analyzed for NH4-N and DRP. Broiler litter increased flow-weighted NH4-N and DRP concentrations from background values of 0.5 and 0.4 mg L(-1), respectively, to values > 18 mg L(-1) in a runoff event that took place immediately after the third application. Ammonium concentrations decreased rapidly after an application and were not strongly related to time after application or runoff volume. In contrast, DRP concentrations tended to decrease more slowly, reaching values near 1 mg L(-1) by 19 mo after the last application. Dissolved reactive P concentrations decreased linearly with the natural logarithm of days after application (p<0.03), and increased linearly with the natural logarithm of runoff volume (p<0.0001).

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