The Asymmetric Leaching Pattern of Nitrate and Chloride in a Loamy Sand Under Field Conditions

Abstract

In a field experiment on a weakly structured, almost stone-free loamy sand, the depths of leaching of chloride and nitrate were measured after sprinkler irrigation at 8 mm/h. The modal depth of movement of the two ions was about half the mean depth of movement, indicating a highly skewed distribution and a pronounced leading tail of chloride and nitrate. The marked asymmetry of the salt distribution is attributed to uneven downward movement of water, including movement down earthworm channels, which results in part of the nitrate and chloride being deeply leached. I Present address : Hudeiba Research Station, Ed Damer, Democratic Republic of the Sudan.

Solute dynamics and the Ontario nitrogen index: I. Chloride leaching

“…2-6). The tracer profile distributions were similar in behaviour and shape to those obtained in field experiments by Burns (1974), Wild and Babiker (1976), and Ward et al (1995), and they are indicative of highly dispersive solute transport through soil with hydraulically active macropores, such as interpedal cracks, biopores, and large intergranular pores (e.g., Jury and Flühler 1992). The rates of Cl TR movement and loss from the profiles varied substantially within and among soils.…”

“…To address these issues, we conducted combined chloride-nitrogen solute transport experiments over a 12-to 15-month period under natural gradient conditions at five field sites in southern Ontario representing the four main HSG categories for agricultural soils (HSG-A, -B, -C, -D). The chloride (Cl) solute was used to trace water percolation and to estimate the profile distributions and maximum potential leaching rates for nitrate (Burns 1974;Wild and Babiker 1976;Jury and Flühler 1992). The nitrogen (N) solute was used to determine actual nitrate leaching rates and profile distributions and to infer nitrate loss via N transformations (Burns 1974).…”

Lateral solute mixing processes — A key for understanding field-scale transport of water and solutes

“…The trust in these equations and corresponding parameter values was founded on the outcomes of laboratory studies with packed homogeneous soil columns in which the Darcy flow and Taylor dispersion (Taylor, 1953) describe the transport regime. Systematic deviations from the expected transport behavior in less homogeneous porous materials (Coats and Smith, 1964), in undisturbed soil columns (Kissel et al, 1973;Cassel et al, 1975;van Genuchten and Wierenga, 1977) and in field soils (Wild and Babiker, 1976) was the inducement for various refinements of the advectiondispersion equation. Field-scale solute transport experiments carried out during the last ten years have shown that the Richards-and the advection-dispersion equation may be valid in some cases and fail in many others (Jury and Flühler, 1992).…”

Soil Faunal Degradation and Restoration

“…Through their interactions with organic matter and microflora, the fauna may cO.ntribute to decomposition and the regulation of nutrient cycling in a manner analogous to that in undisturbed ecosystems (House et aI., 1984;Hendrix et aI., 1986;House and Brust, 1989). Earthworm activity improves water movement and aeration in no-till soils (Wilkinson, 1975;Shipitalo and Protz, 1987), and can reduce surface crusting (Kladivko et aI., 1986), although surface casting could contribute to soil erosion and crusting in areas exposed to raindrop impact (Sharpley et aI., 1979;Shipitalo and Protz, 1988), while preferential flow of water in worm channels could result in loss of nutrients (and pesticide residues) to groundwater (Wild and Babiker, 1976;Bouma et aI., 1982).…”