Acid‐Subsoil Amelioration: II. Gypsum Effects on Growth and Subsoil Chemical Properties

Abstract

In many highly weathered soils crop exploitation of subsoil moisture reserves is severely curtailed by toxic levels of Al. Since vertical movement of lime is usually extremely slow in such soils, specialized mechanical and/or chemical procedures are required to overcome the problem. A field experiment with maize (Zea mays L.) on a strongly acidic Plinthic Paleudult examined the effects of surface‐incorporated gypsum on yield, root development, and profile chemical properties for four cropping seasons. The effects of gypsum (10 Mg ha⁻¹) were time dependent, but by the fourth season had resulted in a cumulative grain yield gain of 3.4 Mg ha⁻¹. Progressive depressions in the level of exchangeable Al were accompanied by increases in subsoil Ca, Mg, and SO₄‐S. Water pH increased markedly in the zone of maximum SO₄‐sorption/precipitation, but pH determined in KCl remained unchanged. By the fourth season the effects of gypsum on subsoil root development were striking. These results indicate that surface incorporation of gypsum is an economically viable approach to subsoil amelioration on soils such as that studied here.