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Dep. of Soil Inventarisation and Land Evaluation, C.T. de Wit Graduate School of Production Ecology, Agricultural Univ., P.O. Box 37, 6700 AA Wageningen, the Netherlands
*Corresponding author (johan.bouma{at}bodlan.beng.wau.nl).
ABSTRACT
Traditional soil structure descriptions are static and qualitative. However, measurement of basic physical and chemical characteristics of a given soil structure followed by simulation modeling of crop yields and water and nutrient regimes results in a dynamic and quantitative soil structure characterization. Within any given soil series, different types of structure may occur as a result of different management practices, and each structure type can thus be characterized. This, however, is a reactive approach in which soil structures are presented as given fact. This paper explores a proactive approach in which measurement of basic soil characteristics on a series of standardized structure samples and exploratory simulation modeling are used to define an "ideal" structure, using plant growth and nutrient-use efficiency as indicators. Management practices to realize such an "ideal" structure remain to be designed by others. Quantitative indicators for the "ideal" structure in the 0- to 30-cm surface soil of a loamy, mixed, mesic Typic Fluvaquent (a prime agricultural soil in the Netherlands) were based on simulated yields and associated nitrate leaching. Simulations considered water supply capacity, occurrence of by pass flow and internal catchment, leaching of nitrates as a function of fertilization scenarios, accessibility of water to roots, and trafficability in spring. Exploratory simulations, using a validated model for a period of 30 yr to express temporal variability for a complete soil profile with varying topsoil structures, showed a structure consisting of 0.5-cm aggregates and a bulk density of 1.6 g cm-3 to be "ideal" for the agricultural land use being considered.
Received for publication September 30, 1997.
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