Least limiting water range: a potential indicator of physical quality of forest soils

The interactions of the 4 basic soil physical properties-volumetric water c ontent, matric potential, soil strength, and air-filled porosity-were inves tigated over a range of contrasting textures and for 3 compaction levels of 4 forest soils in New Zealand, using linear and non-linear regression meth ods. Relationships among these properties depended on texture and bulk dens ity. Soil compaction increased volumetric water contents at field capacity, at wilting point, and at the water contents associated with restraining so il strength values, but decreased the water content when air-filled porosit y was limiting. The integrated effect of matric potential, air-filled poros ity, and soil strength on plant growth was described by the single paramete r, least limiting water range (LLWR). LLWR defines a range in soil water co ntent within which plant growth is least likely to be limited by the availa bility of water and air in soil and the soil strength. Soil compaction narr owed or decreased LLWR in most cases. In coarse sandy soil, initial compact ion increased LLWR, but further compaction decreased LLWR. LLWR is sensitiv e to variations in forest management practices and is a potential indicator of soil physical condition for sustainable forest management.