Water retention and penetration resistance equations for the least limiting water range

Abstract

The least limiting water range is a soil physical quality indicator, which is useful to predict the optimum water range for plant growth in a given soil and to study the effects of soil use and management over this optimum water range by integrating the effects of available water, penetration resistance and air filled porosity. This study tested six equations to fit water retention and penetration resistance surface responses used to determine the least limiting water range and present a simple algorithm written in the open source software R for fitting, calculation and visualization of the least limiting water range. Five soils from Brazil and Canada, under different use and management conditions were used to test the functions. The results show that the three water retention surface responses had good statistical properties for fitting water retention and that two of the penetration resistance surface responses were adequate to fit the data, while one failed to achieve convergence in two instances. The open source code performed as well as the commercial statistical package SAS for fitting the penetration resistance and water retention equations.

Physics of Soil and Other Natural Porous Media

“…Penetrometer resistance measurements should never be used without checking soil water content and bulk density as it is an exponential function of these two soil variables (Figure 6.8). An empirical relationship between soil penetration resistance, bulk density and water content usually encountered on the literature is [62] SR = a 0 ρ a 1 θ a 2 (6.8)…”