A QUANTITATIVE AUSTRALIAN APPROACH TO MEDIUM AND SMALL-SCALE SURVEYS BASED ON SOIL STRATIGRAPHY AND ENVIRONMENTAL CORRELATION

Current methods of soil survey and land evaluation arc based on transf er by analogy and results can be limited by the quality of the classif ication system used for mapping. Parametric soil survey is an alternat ive where predictions of individual soil characteristics and qualities , rather than soil types, are provided for the complete survey area. P redictions can be derived from either local soil classifications or in terpolation and surface fitting procedures. The feasibility for a thir d approach to parametric survey has been investigated using data from the lower Macquarie Valley, NSW, Australia. Soil characteristics were predicted using generalized linear models with more readily observed e nvironmental variables as predictors. These variables (e.g. geomorphic unit, local relief, etc.) are related to pedologic factors controllin g soil distribution. A large percentage of variation for most soil cha racteristics was accounted for by pedoderms which were mapped using st ratigraphic relationships determined in the field and by air photo int erpretation. (Variation accounted for in the A horizon: clay content=6 3.9%, CEC=66.5%, EC=26.5%, pH=43.0%, bulk density=33.3%, COLE=61.2%, - 10 kPa gravimetric water content=66.4%,-1.5 MPa gravimetric water cont ent=64.0%; B horizon: clay content=34.9%, CEC=58.2%, ESP=41.5%, EC=17. 2%, pH=33.3%, bulk density=32.1%, COLE=59.9%, -10 kPa gravimetric wate r content= 55.5%, -1.5 MPa gravimetric water content=39.8%). Within-pe doderm statistical models were developed with landform as an explanato ry for several units and these further improved predictions. The poten tial of the approach in routine soil survey is discussed and the advan tages of generalized linear models for analysing survey data are noted .