Reclamation of a failed subsurface drainage system on an unstable clay soil

Abstract

The soil structure of a dispersive clay soil on which a subsurface drainage system had failed was modified by applying gypsum (5 t/ha) and growing a crop of sunflowers. The sunflower crop and gypsum application increased macroporosity from 8 to 15% and stabilised the clay microstructure. Sunflowers without gypsum produced a similar increase in soil macroporosity but with a potentially more dispersive clay microstructure. Gypsum alone produced a stable clay microstructure and intermediate values (about 11%) of macroporosity. The yield of wheat was similar on both drained and undrained areas (4 t/ha) following the sunflower crop with and without gypsum application, whereas on untreated areas, yields were 2.1 t/ha in the absence of drainage and 3.3 t/ha when drained.