Effect of tillage and stubble management on soil water storage, crop growth and yield in a wheat-lupin rotation in southern NSW

Abstract

The effects of tillage (conventional tillage v. direct drilling) and stubble management (stubble retained v. stubble burnt) on soil water storage, growth and yield of wheat were assessed over two seasons (1989-1990) in a wheat-lupin rotation on a red earth at Wagga Wagga, NSW. Soil water storage and efficiency of water use were different for the two seasons. Both direct drilling and stubble retention maintained the soil surface (0-0.1 m) at higher water content at sowing time. However, their effectiveness in increasing soil water storage at sowing was evident only in the 1990 season which, with average rainfall during the summer fallow, was drier than 1989. Average wheat grain yield was similar (4.02 v. 4.08 t/ha) for the two seasons even though the 1989 season had 245 mm more rain, the difference mainly occurring in March-April. Most of the excess water in seasons like 1989 was likely to have been lost by deep drainage, with implications for leaching of soluble nutrients, increasing subsoil acidity and rising watertables. Poor early growth of wheat when the stubble was retained and the crops direct drilled was season dependent. It was observed in the wheat crop only in the 1989 season which had a wet autumn. In that season, poor early growth which resulted in a significant yield reduction of 0.5 t/ha was associated with reduced water extraction before anthesis despite the availability of adequate soil water. No corresponding differences in growth and yield were observed for the lupin crop.