Geography of Soil Test Results
1976
Westin, Frederick C.
Since the factors that control soil formation and soil geography must also affect levels of soil K, P, organic matter, and pH, this study was undertaken to determine the correlations that might exist between soil geography and soil test results. Soil test results for over 80,000 farmer samples were correlated with soils classified at the series, family, subgroup, great group, suborder, and order categories of the comprehensive soil classification system. Then the regional effects of climate and native vegetation on soil test results were isolated, followed by a determination of the local effects on the soil test results of soil parent material, slope and age. Chi square statistical procedures were used to determine significance. Increasing precipitation resulted in decreased K and P and lower pH but higher organic matter. Increasing temperature lowered K and organic matter and increased P but had no effect on pH. Within a climatic zone, as sandiness increased, levels of K, P and organic matter decreased, while pH rose. When carbonate content increased, K and P decreased and pH increased, while organic matter remained constant. As slopes became steeper, levels of K, P, and organic matter decreased, while pH rose. And as soils became older, K and pH decreased, while P and organic matter remained essentially constant. Except for the influence of soil texture on organic matter, all other data were highly significant. Although precise amounts of K, P, organic matter and pH require individual field sampling, a consideration of the geography of the soils as expressed in soil taxonomic terms gives a rational starting point in plant nutrient assessment and a tool for extension of fertility-related data.
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