Detachment of Soil as Affected by Fertility Management and Crop Rotations

An experiment was initiated on Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in 1981 to compare the effects of fertility management and crop practices on splash detachment of soil. Experimental treatments included comparisons of crop rotations of soybean [Glycine max (L.) Merr.| after corn (Zea mays L.) (SB), corn after soybean (C), and oat/red and yellow sweetclover (Avena saliva L./Trifoliumpratense L. and Mellilotus officinalis Lam.) after corn (O/CL). For each crop rotation, there were two management options, either added manure (OR) or herbicide plus chemical fertilizer (HF). The seventh treatment was continuous corn (CC) with herbicide, chemical fertilizer, and insecticide. Soil surface samples from each treatment were subjected to rainfall intensities of low (35 mm h~'), medium (62 mm h'), and high (120 mm h~'). Total splash detachment of soil from simulated rainfall was linearly related to rainfall intensity. For all crop rotation treatments, total splash detachment generally was greater for manured soils than from soil with herbicides and fertilizer. Continuous corn had the lowest soil splash detachment at low intensity, second highest splash detachment at medium intensity, and the highest splash detachment at high intensity. This trend clearly indicated that rate of splash detachment of CC was higher than from soil under crop rotations. The splash detachment rates were 48, 40, 39, and 31 mg cm~ for CC, C, SB, and O/CL, respectively. Treatment by rainfall intensity interaction was significant, which suggested that intensity and crop rotation were not independent in their effect on soil splash detachment. Soil aggregation as inferred from geometric mean diameter (GMD) indicated that CC had the lowest degree of aggregation (150) as compared to 211 for C, 225 for SB, and 313 for O/CL. S EROSION involves two stages: (i) detachment of soil particles, and (ii) transportation of the soil material by erosive agents such as water or wind. Soil detachment by raindrops is the initial phase of the soil erosion process by water. Soil detachment can also occur due to overland flow of water during a rainfall event. This study deals with soil detachment due to splash. Soil management practices such as residue placement, manuring, and crop rotation may have both direct and indirect effects on soil physical properties. Soil properties in turn affect the characteristics of the detachment process. Singer et al. (1981) tested the effects of mulch rate of oat on soil detachment by raindrop splash and subsequent transport. They used a 300by 300-mm plot area with catch trough arrangement that would measure both overland flow and sediment transport in addition to splash from the plot. Using 3.2-mm diam. raindrops at an intensity of 76 mm h~' for 30 min with a 2.5-m high rainfall simulator, they reported a reduction in sediment in interrill flow from 83 g with no cover to 20 g with 222 g m~ cover (96% cover). Splash was reduced from 17.9 g with no cover to 1.4 g with 222 g m~ cover rate, which represents a reduction factor of 13. Further, they concluded that splash detachment and transport are both linearly reduced between no cover and 96% soil cover. Feedlot manure has a significant effect on soil detachment through its effect on soil physical properties. Low rates of manure application improve physical properties of the soil (Outlay et al., 1956), such as water-holding capacity of the soil (Olson et al., 1970) and infiltration rate (Murphy et al., 1972). Heavy application of manure containing large amounts of monovalent cations deteriorated the physical condition of the soil. Mazurak et al. (1975) indicated soil detachment of 55 mg cm~ of water for nonmanured soil compared to 89 mg cm~ of water for soil with manure S.K. Hussain and J. Skopp, Dep. of Agronomy, and L.N. Mielke, USDA-ARS, Keim Hall, East Campus, Univ. of Nebraska, Lincoln, NE 68583. Contribution from the USDA-ARS in cooperation with the Agric. Res. Division, Univ. of Nebraska, Lincoln. Published as Paper no. 8353, Journal Series, Agric. Res. Division. Received 26 May 1987. "Corresponding author. Published in Soil Sci. Soc. Am. J. 52:1463-1468 (1988). 1464 SOIL SCI. SOC. AM. J., VOL. 52, 1988 rates of 415 t ha~' y~'. They also reported that manured soil contained the largest aggregates, up to 4760 ^m in diameter as compared to an upper limit of 1190 jim for nonmanured soil. They suggested that aggregates in manured soil may be detached, but not easily dispersed by raindrops. Indirect effects of soil physical properties on detachment occur through their influence on the strength of the aggregates. Al-Durrah and Bradford (1982) found that soil detachment increased with decreasing bulk density and increasing soil water content. Epstein and Grant (1967) found the greatest amount of splash from soil with low clay content and high sand content. It might be expected that properties such as bulk density, infiltration rate, saturated hydraulic conductivity, and organic matter will also indirectly influence detachment. Knowledge of the mechanics of raindrop impact is essential in understanding soil detachment. Palmer (1965) studied waterdrop impact on thin water layers above the soil surface. He used drop diameters of 2.9, 4.7, and 5.9 mm, and found that maximum impact depends on the depth of water layer. He denned the depth at which maximum impact force is achieved as the critical depth. The critical depth for drop diameters of 2.9, 4.7, and 5.9 mm are 2.0, 4.0, and 6.0 mm, respectively, which is nearly equal to the drop diameter. He also found that stress resulting from waterdrop impact for water layers of critical depth did not increase proportionally with drop diameter. Mutchler and Larson (1971) conducted experiments to study detachment of glass beads 76 mm in diameter. Water depth, waterdrop mass, and drop diameter were used to study their effect on detachment. The greatest amount of soil detachment occurred when the ratio of water depth to rainfall drop diameter varies from 0.14 to 0.24, depending on the mass of the drop. Objectives of this research were to determine (i) the influence of fertility management of manure and herbicides plus fertilizer, and crop management of crop rotations and monocultural systems on detachment of soil particles by raindrops; and (ii) the influence of rainfall intensity on detachment and diameter distribution of detached sediment. We hypothesized that continuous cropping would result in poorer soil physical properties and, therefore, greater detachment, and that manured treatments would result in greater detachment due to greater dispersion from large amounts of monovalent cations in the manure.