Changes in root growth within successive wheat crops in a cropping cycle using minimum and conventional tillage

Abstract

The aim was to describe, through a cropping cycle of four years of successive wheat, root growth following different times of sowing using minimum or conventional tillage in the central west of New South Wales. The hypothesis was that, due to transient differences in soil structure at sowing, early growth of roots would be retarded under minimum tillage, but that eventually root growth would be better under minimum tillage than under conventional cultivation because of long-term changes in soil structure and infiltration characteristics. Minimum tillage did cause total root length to be less in the seedling stage in the first three years, whereas root length was the same in later growth in the early years, and greater under minimum tillage than under conventional cultivation in the later two years of the cropping cycle. Tillage, time of sowing or cultivar did not affect the relative distribution of roots with depth; treatments also did not affect maximum root depth, which increased during the development of each crop to an asymptote of only 75 cm. Minimum tillage resulted in higher rates of water infiltration to the soil at the end of the cropping cycle, and in higher soil water and greater crop water use during the cycle; minimum tillage did not result in statistically higher grain-yields compared with conventional cultivation. Relatively low grain-yields and low water-use efficiencies, particularly in years of above-average rainfall, implied over-riding constraints probably associated with poor soil structure, on crop performance.