10 YEARS OF A MAIZE OATS ROTATION UNDER 3 TILLAGE SYSTEMS ON A SILT LOAM IN NEW-ZEALAND .1. A COMPARISON OF SOME SOIL PROPERTIES

The effects of zero, minimum and full tillage (mouldboard plough) on some properties of a fine textured, imperfectly drained, loess soil (Aeric Fragiaqualf) under a maize/oats rotation in New Zealand were investigated after 10 years of continuous cropping and compared with an adjacent pasture site. Zero tillage resulted in higher soil bulk densities, larger soil aggregates and lower total porosities compared with full and minimum tillages. However, there were no significant differences (P < 0.05) in the saturated hydraulic conductivities of soil cores taken from the top 100 mm of each tillage treatment immediately before preparation of seedbeds. After full and minimum tillage, infiltration rates were greater than for zero tillage. Aggregate stabilities were assessed in each treatment and in an adjacent area under permanent pasture by wet sieving. Continuous cropping caused a decline in aggregate stabilities, compared with pasture. Soil strength as measured by a cone penetrometer, was substantially higher in the 50-250 mm layer under zero tillage and minimum tillage compared with the full tillage treatment. Carbon contents and cation exchange capacities were lower in the cropped soil compared with those in adjacent pasture after 10 years of cropping, particularly at the surface of the full tillage treatment, because of redistribution of soil. Different tillage practices gave rise to different distribution patterns of nutrients in surface layers. In the 0-50 mm depth, the nutrients P and exchangeable K and increases in pH caused by lime addition were greater under zero tillage than for full or minimum tillage where more soil mixing occurred. Minimum tillage would appear to be the most advantageous technique for continuous cropping on this soil, as on balance it best preserves soil chemical and physical fertility.