LONG-TERM EFFECTS OF CONVENTIONAL AND NO-TILLAGE ON SELECTED SOIL PROPERTIES AND CROP YIELDS IN CANTERBURY, NEW-ZEALAND

There is considerable interest in the possible use of no-tillage farming systems to extend the arable phase of mixed cropping farming systems in New Zealand. Changes in a range of soil physical and chemical properties, earthworm populations and crop yields were compared under conventional tillage (CT) and no-tillage (NT). Trials were conducted for 9 consecutive years at two sites. The Lismore site had been under long-term pasture prior to initiation of the experiment, whilst the Wakanui site had been under long-term arable cropping. At the Lismore site, organic C and total N contents in the top 150 mm of soil declined under both treatments during the trial, although the decrease was relatively greater under CT. Tillage treatment had little effect on soil organic matter content at the Wakanui site. At both sites, organic matter was more evenly distributed in the top 150 mm of soil under CT than NT. Bulk density was largely unaffected by tillage treatment on the Lismore soil, but on the Wakanui soil it was greater under NT at 0-150 mm depth throughout most of the trial. For both the Lismore and Wakanui soils, macroporosity was generally less in the surface (0-75 mm) layers of uncultivated soil. At both sites, earthworm populations were greater under NT than CT. Yields of wheat tended to be greater under NT at both sites, with crops grown under CT requiring an additional 15-45 kg N ha-1 to obtain yields similar to those under NT. At the Wakanui site, by contrast, spring barley yields were greater under CT with an additional 10-20 kg N ha-1 required under NT to provide yields similar to those under CT. Under CT there is a flush of mineralization following cultivation, whilst under NT mineralization is more evenly distributed over the growing season. Crops grown following cultivation in autumn/winter have a more adequate N supply during the growing season under NT than CT, as much of the N which is mineralized after cultivation of CT soil is susceptible to leaching before the spring. Crops grown following cultivation in the spring have a more adequate N-supply than those under NT, as the flush of N mineralization under CT occurs immediately prior to the onset of rapid crop growth.