TILLAGE AND WATER-CONTENT EFFECTS ON SURFACE SOIL PHYSICAL-PROPERTIES

The effects of pre-tillage soil water content (PTSW) and multiple-pass tillage on soil physical condition was investigated on a silt-loam soil susceptible to wind erosion. PTSW was shown to affect the soil condition produced by tillage and an interaction between intensity of tillage and PTSW was identified. The 'excess' tillage treatment produced 13.9% of aggregates < 0.26 mm diameter when PTSW was 0.58 times the lower plastic limit as compared with 6.0% when PTSW was equal to the lower plastic limit (highly significant). On this soil the avoidance of excessive tillage reduced the likelihood of a significant PTSW effect. Aggregates produced from 'excessive' tillage were more stable than those from the 'intermediate' and 'minimum' tillage treatments when dry aggregate stability was determined soon after tillage. Aggregates formed during tillage with PTSW near the plastic limit were less resistant to mechanical breakdown when compared with those formed at lower PTSW levels. Excessive tillage at the lower plastic limit and at 0.58 times the lower plastic limit resulted in dry aggregate stability indices of 0.835 and 0.923, respectively (significant). More intense tillage produced a smoother soil surface, which increases the susceptibility of the soil to wind erosion. Random soil roughness and soil surface area were not affected by PTSW. Dry bulk density was lower for 'minimum' tillage as compared with the other two treatments. Excessive tillage of this soil should be avoided, especially at low PTSW, because of the large quantities of wind-erodable aggregates which can result. In assessing the most appropriate PTSW for desired tillage objectives, the effect on aggregate stability must be considered.