Repetitive aerial photography can be used to help identify and evaluate variation within soil mapping units. An area of approximately 12 ha (30 acres) was photographed from a light plane with two 35‐mm cameras using color and color infrared film on 20 different dates from May through November 1969. This sequence of aerial photographs recorded changes in surface soil moisture patterns and documented a close correlation to patterns of differences in growth and maturation of corn (Zea mays L.) that were visible later on during the growing season.Field investigation of soil profiles in the study area established the relationship of these patterns of surficial soil moisture and crop growth to variations in soil profile characteristics, especially depth of solum, thickness of silt mantle and soil drainage class. The yield of ear corn associated with delineated areas of crop and soil patterns ranged from 5,865 to 9,087 kg/ha. Differences in crop growth and yield were attributed to variations in the amount of available soil moisture, as influenced by soil profile characteristics and surface topography.
Pedographic modal analysis expresses soil composition in terms of the relative amounts of constituents observed in thin sections.Data are presented on the sampling density necessary for pedographic modal analysis of an argillic horizon. Thirty-one randomly selected samples (lOOcc cores) were obtained from a 61 cm by 61 cm vertical exposure of the horizon. Four thin sections were made from each core. Six constituents were counted in each thin section by the point count method of modal analysis. Constituents less than 50 p. in diameter were classified as matrix, while those larger than 50 M were classified as glaebules, pores, papules, argillans, or skeleton grains.Results indicate that a sample adequate to measure these constituents in an argillic horizon with a standard error 10% of the mean would involve taking 21 cores, making 2 thin sections per core, and counting 1,000 points per thin section.
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