Landforms in the rice - growing areas of the Cagayan River basin

This paper reports on a project to devise and test, in the Cagayan River Basin in the Philippines, a procedure for rapid land description beneficial to agriculturalists. Against a background discussion of the foundations of land classification, various geomorphic-pedogenic studies, and of different land classification systems, the authors describe the evolution of landforms, the stratigraphy, and the climate of the study area. They adopted a hierarchical four-level classification system consisting of: (1) four land systems (alluvial, plain, hill, and mountain); (2) nine land subsystems; (3) 30 landform units; and (4) 75 homogeneous land surface units. All Basin land was mapped to the subsystem level, but only land in the alluvial system, where rice production is concentrated, was mapped at the landform unit level. Patterns within the 150,000 ha study area were identified from topographic maps, stereograms, and LANDSAT imagery. The three highest levels were characterized in terms of surface features, land use, vegetative cover, water availability, flooding hazards, and suitability for rice cultivation. Next, to obtain a limited but objective evaluation of the correspondence between landform and soils, soil profile data were gathered from 26 sites (40cm of surface) along seven short transects. Subsequent cluster analysis of the profiles and review of the resulting pattern of fusion supported the presence of a correlation between landform units and soil properties. Although the hierarchical system was applied satisfactorily in Cagayan, the procedures by which the system was formulated must be tested in other regions, both in the 2-300,000 ha range and in areas in excess of 1,000,000 ha. Also, additional studies are needed to determine the degree of correspondence between land forms and soil characteristics and between these soil properties and crop adaption. The report includes numerous tables, graphs, and photographs and a list of 35 references (1951-80).