Amelioration of dense sodic subsoil using organic amendments increases wheat yield more than using gypsum in a high rainfall zone of southern Australia

Subsoil constraints are major limiting factors in crop production in many soils of southern Australia. A field study examined effects of deep incorporation of organic and inorganic amendments in 30–40 cm on soil properties, plant growth and grain yield of wheat (Triticum aestivum var. Ambrook) on a Sodosol with dense sodic subsoil with or without lucerne history in a high rainfall region (long-term average annual rainfall 576 mm) of Victoria. Amendments were applied at a rate of 10–20 t ha−1. Deep ripping alone and deep ripping with gypsum did not significantly affect grain yields. In comparison, application of organic materials doubled biomass production and increased grain yield by 1.7 times. Organic amendment-treated plots produced 60% more grains per area than the untreated control. The crop extracted over 50 mm extra water from below 40 cm soil in organic amendment-treated plots than the untreated control. Nitrogen uptake was almost doubled (403 kg ha−1) in the organic amendment-treated plots than the untreated control (165 kg ha−1). The improved yield with amendments was related to an increase in plant available water in the hostile subsoil, and prolonged greenness of leaves and supply of nitrogen and other nutrients.