ABSTRACT:
In an earlier study, it was shown that short-term (< 1 h) infiltration rates in the conventionally-tilled treatment (CT) of a 10-year-old tillage study near Griffin, Georgia, were reduced compared to the no-till treatment (NT), because of the presence of a surface crust. Our objective was to determine whether macropores were present in the NT treatment of this study and, if so, what effect macropores might have on the infiltration rate in NT and on chloride movement. We measured steady-state infiltration rates in the field with 98 cm (38.6 in) diameter rings. Macropore distributions were measured on intact soil columns 30 cm (11.8 in) in diameter and 40 cm (15.7 in) in length using ultramarine blue dye. We also used columns to determine the effect of a small simulated rain of 1 cm (0.4 in) immediately after chemical application on chloride (Cl) leaching in a larger rain of 16 cm (6.3 in) one week later. Macropores were evident near the surface in the NT treatment and constituted 15% of the cross-sectional area based on image-analysis of the dye stains. Long-term (> 2 h) steady-state ring infiltration rates were not reduced in NT plots compared to CT, in spite of a shallow hardpan in NT; this was arributed to macropores that penetrated the hardpan. A 1-cm rain immediately after chemical application reduced leachate concentrations of Cl by about half in both the NT and CT treatments. With the 1-cm initial rain, chloride had an apportunity to diffuse into stagnant regions of the matrix and as a result was excluded from flow in macropores and interaggregate space. Macropores will probably cause the greatest leaching losses when a chemical is applied to the surface of NT and a large rain occurs soon after application.
Footnotes
M. H. Golabi, formerly a graduate student at the University of Georgia, is now a post-docvoral associate, Department of Agronomy, Purdue University, West Lafayette IN 47907; D. E. Radcliffe is an associate professor, Crop and Soil Science Department., University of Georgia, Athens 30602; W. L. Hargrove is a professor, Crop and Soil Science Department, University of Georgia, Griffin 30223; and E. W. Tollner is a professor, Department of Biological and Agricultural Engineering, University of Georgia, Athens 30602.
- Copyright 1995 by the Soil and Water Conservation Society
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