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Effects of Soil Surface Management on Water Flow Distribution and Solute Dispersion

North American Environmental Chemistry Laboratory, Dowelanco, Bldg. 306/A-2, 9330 Zionsville Rd., Indianapolis, IN 46268-1053

W. A. Jury

Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521-0424

*Corresponding author.

ABSTRACT

A known benefit of cultivation is increased infiltration rates during subsequent irrigation or precipitation events. This study was conducted to investigate the effects of cultivation and irrigation method on uniformity of water flow and dispersion of solutes leached through a Tujunga loamy sand (mixed, thermic, Typic Xeropsamment) at Etiwanda, CA. Outflow from undisturbed, unsaturated field soil contained in a 0.8 by 0.8 by 0.3 m lysimeter was sampled by a 64-cell grid of fiberglass wick solution samplers. Daily 20-mm water inputs were applied at a rate of 5 mm h^–1 for 4 h by hydraulic spray nozzles (HSN) mounted on a motorized boom or by low-volume sprinklers (LVS). Narrow pulse inputs of Cl^–, NO^–₃, and Br^– solutions were used to evaluate solute dispersion and travel paths. Four experiments were conducted sequentially in the same lysimeter: (i) light raking, broadcast Cl^– and local NO^–₃, and HSN, (ii) light raking, local Cl^–, HSN, (iii) shallow cultivation and releveling, no solute, and LVS, and (iv) broadcast Br^– and HSN. Based on drainage positions observed with locally applied solutes, flow appeared to be one-dimensional through most of the transport volume. Switching from HSN to LVS and then back to HSN apparently had much less effect on water-flow variation than did shallow cultivation and releveling. The overall trend with time was decreasing variability in locally measured water flow, and only in the last experiment were the flow patterns time invariant. Areaveraged solute breakthrough curves for transport experiments conducted before and after cultivation showed less dispersion following cultivation. The decrease in solute spreading estimated from fitted convection-dispersion model parameters and by travel time moment analysis was of similar magnitude to the reduced variation of the locally measured water flows. Shallow cultivation appeared to lower the hydrodynamic dispersion of the flow field at the scale measured in this study, thus decreasing the spreading of the leached solute pulse.

Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA.

Received for publication August 13, 1992.

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