Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

Abstract

Abstract Highly weathered soils in the southeastern USA often have very acid, hard, infertile subsoils not readily penetrated by crop roots. An experiment on a Typic Hapludult involving deep liming, subsoil disturbance and mixing, and surface application of gypsum was conducted to investigate the possibilities of ameliorating such subsoils. Results with alfalfa ( Medicago sativa L.) over 4 yr show that liming to 1 m can increase yields by 50% while merely mixing the subsoil without lime incorporation resulted in a substantial yield decline. Surface application of gypsum with sufficient time for it to penetrate the subsoil resulted in 25% yield increases. Deep liming resulted in the complete precipitation of soluble Al and increased the level of soluble Ca allowing roots to freely penetrate the subsoil. Gypsum resulted in a progressive reduction in soluble Al and an increase in soluble Ca creating a similar but lesser effect than liming. Water extraction patterns corroborated the fact that roots were penetrating chemically ameliorated subsoil. Saturation extract studies indicated that gypsum reduced the activity of Al 3+ and increased that of Ca 2+ substantially. These results suggest that by‐product gypsum from phosphate acid manufacture would be a feasible amendment for acid subsoils.