An Algorithm for Calculating the Least Limiting Water Range of Soils

The least limiting water range (LLWR) is used to estimate the optimum soil water content for plant growth based on the range of bulk density values for a given soil series under evaluation. However, the use of this methodological approach by soil scientists has been limited by the lack of a detailed description of the statistical and mathematical procedures used for its calculation. This paper describes a Statistical Analysis System (SAS) algorithm for calculation of the LLWR from bulk density, volumetric water content, water potential, and soil penetration resistance data. Since nonlinear regression techniques are used, a brief description of the theory involved in this type of statistical analysis is presented. To improve the visualization and interpretation of the LLWR results, a plotting subroutine is also described. Five soils with different textures and management conditions were used to validate the algorithm. Statistical comparison with previously published LLWR calculations showed that the new method is reliable and accurate and can substantially reduce the time and labor necessary to estimate the LLWR of soils.