The relationship between soil classes, soil properties, plant growth and soil management treatments in the Goondi Mill area of North Queensland, Australia

Typescript.Thesis (Ph. D.)--University of Hawaii, 1967.Bibliography: leaves 202-209.xiv, 209 l illus., mapsMost definitions of soil have included references to its function as a medium for plant growth. Several investigators believe that because correlations between soil classes and crop yield are weak, conventional soil surveys are of little value. According to these workers, soil groupings based on "edaphic" trials are more useful for predictions of crop yields. Argument is presented in this dissertation to show that soil properties are most unlikely to correlate directly with crop yield but relationships between soil properties and plant growth responses to management treatments should be feasible. The study reported here sets out to establish the following hypotheses: 1. That each soil class based on a combined morpho1ogica1genetical system of classification has a different group of "key" properties. 2. That each different group of properties has a different influence on plant growth and the response to management techniques. The hypotheses are examined by studying soils growing Sugar Cane (Sacharrum offinarum) in the Goondi area of North Queensland, Australia. The geology and physiography of the area is described. Soils of the area are described, classified, and mapped. The more important soil types are selected for further study and for quantifying those soil properties which are related to the root environment and plant growth. Charge characteristics, charge population, clay mineralogy, and "free" iron oxide content assist in predicting the nature of nutrient pools within soils and the wastage of plant nutrients through chemical reaction or leaching. Atterberg limits are related to water retention characteristics, and soil aggregate strength. Macroporosity and Atterberg limits are related to permeability. The important soils are characterized in terms of these factors. Methods for recognizing the possibility of root impedance, the degree of oxygen shortage for root respiration, and the relationship of root impedance and oxygen shortage to root and plant growth have not been clarified, according to the available literature. Experiments are therefore undertaken to show that macroporosity, bulk density, and soil strength can all be related to root growth but the measurement of soil strength (using a penetrometer with a fine tip) is a satisfactory means of predicting root growth restriction. Several workers have shown that for unsaturated conditions, soil strength is more likely to limit root growth than a shortage of oxygen. If this is so the problem of a shortage of oxygen in soils only occurs under saturated or near-saturated conditions. Preliminary experiments indicated that oxygen in saturating waters was used rapidly although metabolic processes continued to operate. Oxygen may be supplied to the plant roots by transfer from the air through the plant stem. Morphological characteristics of soil profiles can be related to water table fluctuations but water table movement can only be related to plant growth in general terms. It is shown that each group of properties has a different influence on plant growth and soil management and that, by correlation methods, each soil class has a different group of properties. Therefore, each soil class has a different influence on plant growth and the response to management practices