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Genetic Association of Properties of Soils of an Area in the Upper Amazon Basin of Peru¹

ABSTRACT

Soil properties of a 400-ha area in the Upper Amazon Basin of Peru were found to be related to the nature of the parent material and to occurrence of defined geomorphic surfaces. The soils are developed from unconsolidated sandy to clay textured river sediments, originating in the Andes Mountains. The oldest surface is presently on the level hill tops. A surface which cuts the higher older surface and grades to the intervening valley floors of the same age and the recent flood plain is the youngest geomorphic surface.

The Typic and Aquic Paleudults of the oldest surface generally have lower pH values, lower base saturation, and contain less weatherable minerals, but contain greater amounts of clay-sized kaolinite than the soils of the younger surface. The soils of the erosional surface are Ultisols, Inceptisols or Alfisols. Genetic control of these soils appears to depend upon the location of an impervious layer which controls ground water depth. The Alfisols, Inceptisols, and Entisols of the flood plain contain about 15% weatherable minerals and high amounts of well crystalized smectite clay minerals that have probably undergone limited pedologic alteration.

¹ Paper no. 5258 of the Journal Series of North Carolina Agric. Exp. Stn., Raleigh, NC 27607. Conducted in cooperation with the Ministerio de Alimentacion of Peru under Contract AID/ta-C-1236 with the U.S. Agency for Int. Development.

² Former graduate Assistant, Soil Science Dep., North Carolina State Univ., now Assistant Professor of Soil Science. College of Agric. and Life Sciences, Univ. of Wis., Madison and the Geological and Natural History Survey, Univ. of Wis., Extension.

³ Professor and Associate Professor, Soil Science Department, North Carolina State University, Raleigh, respectively.

Received for publication June 1, 1977. Accepted for publication April 28, 1978.

This article has been cited by other articles:

				P. A. Sanchez, P. A. SANCHEZ, and J. R. BENITES Low-Input Cropping for Acid Soils of the Humid Tropics Science, December 11, 1987; 238(4833): 1521 - 1527. [Abstract] [PDF]