Defining the "ideal" soil structure in surface soil of a typic fluvaquent in the Netherlands

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 manage ment 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 indica tors 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 bypass 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.