Effect of cropping on the physical fertility of krasnozems

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Abstract
The physical properties of krasnozems and euchrozems in Australia have received little attention due to the widespread perception that they are 'good' soils. We present data from three locations which are representative of these soil types in the South Burnett region of southern Queensland. At each location, paired sites were chosen where continuously cropped and uncropped land existed side by side. The effect of continuous cropping on physical fertility, relative to that of soil in virgin condition, is assessed and related to published data from other locations where available. Continuous cropping has reduced infiltration rates from 80 mm h-1 or more to values as low as 25 mm h-1. Originally low bulk densities ranging from 0.6 Mg m-3 at the surface to 1.3 Mg m-3 at 70 cm depth have been increased to corresponding values of 1.0 and 1.4 Mg m-3. Local maxima of 1.3 Mg m-3 occur between 15 and 30 cm depth. Penetration resistance has been increased markedly at low water contents as a result of increased cohesion, with an uncropped soil having values 6 MPa in the continuously cropped soil. Organic carbon in the surface soil has been reduced from 4-5% to 1% and aggregate stability under rain has been reduced, the % aggregates

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