Soil physical conditions after six years of direct drilling or conventional cultivation on a silt loam soil in New Zealand

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Abstract
Soil physical conditions following six years of cereals planted by direct drilling (DD) or conventional cultivation (ploughing, PL) are compared. Bulk density was higher in the top 200 mm of the DD soil but, with ploughing, bulk density was found to increase sharply and remain higher than DD below this depth. With DD, soil strength was consistently higher at most depths and aggregate stability was also higher. Earthworm numbers were at least 1.5 times greater in the DD plots. Infiltration rates were similar under both systems despite the lower total porosity and air-filled porosity of the DD soil. This was attributed to a more open and continuous network of pores in the DD soil. Root densities measured in the same year as the soil physical conditions were significantly higher in the surface 0-100 mm of the DD soil and also tended to be higher below 200 mm depth. In the sixth year of the trial, there was a significantly greater plant emergence in the DD soil than PL soil, although harvest grain yields were similar for both treatments.