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Effects of Land Clearing and Subsequent Management on Soil Physical Properties¹

ABSTRACT

Large scale, mechanized land clearing is common in the humid tropics even though little attention has been given to defining and solving soil problems that may be created. The purpose of this study was to evaluate various combinations of land clearing method, burning of vegetation, post clearing tillage, and soil management on soil physical properties of a forested Ultisol in the Amazon basin. Land clearing methods used were (i) slash, (ii) bulldozer clearing with a straight blade, and (iii) bulldozer clearing with a shear blade. Specific effects associated with clearing were mechanization, bulldozer blade type, burning, disking, and chiseling. Post clearing soil management systems isolated effects of bedding, liming, and fertilization. Soil physical properties were measured before clearing and 14, 29, and 98 weeks after clearing. Compaction increased bulk density (_b) of the 0- to 15-cm depth for all clearing methods, but _b of the 15- to 25- depth increased by 0.1 Mg m^–3 only for the bulldozer cleared treatments. Soil texture of the 0- to 15-cm depth was not altered by land clearing. Gravimetric water content at soil matric potentials < –2 kPa was greatest for the straight blade cleared soil. The infiltration rate 14 weeks after clearing decreased 37, 96, and 90% for soil cleared by slash, straight blade, and shear blade, respectively, as compared to initial conditions. Chisel plowing and disking the newly cleared land increased the infiltration rate compared with straight blade without chiseling. Detrimental changes in soil physical properties caused by clearing were minimized when post clearing management practices of bedding, fertilization, and liming were adopted.

¹ Contribution from the Dep. of Soil Science, North Carolina State Univ. Paper no. 10043 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601. This study was funded in part by the TROPSOILS program, U. S. Agency for International Development.

² Visiting Assistant Professor, Professor, and Visiting Associate Professor of Soil Science, North Carolina State Univ., Raleigh, NC 27695-7619.

Received for publication November 29, 1985.

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