Cotton Growth in an Acid Fragipan Subsoil: I. Effects of Physical Soil Properties, Liming, and Fertilization on Root Penetration

Abstract Roots of established cotton ( Gossypium hirsutum , var. ‘Rex’) seedlings were allowed to grow into undisturbed or laboratory‐prepared cores of an infertile, highly acid, compact fragipan subsoil (Dickson series). A significant positive correlation was found between the number of roots in the subsoil cores and soil moisture. Examination of thin sections revealed a low total porosity and a predominance of small, discontinous planar voids in Dickson fragipan, which apparently contributes to the narrow range of available water in this horizon. The number and dry weight of roots decreased with increase in bulk density; however, the 1.5 g/cm 3 bulk density of the fragipan is not considered an important factor for cotton root penetration in this subsoil. Root growth was not consistently related to soil strength as measured with a penetrometer probe. Significantly greater root dry weights and depth of penetration were found in limed than in nonlimed cores, regardless of bulk density, soil strength, or NPK fertilization. Results of this study indicate that adverse chemical or physiological effects related to extreme soil acidity may be dominant over other physical and chemical factors that inhibit root growth in Dickson fragipan subsoil.