The effects of tillage and zero-tillage systems on soil aggregates in a silt loam

Abstract

Three seedbed preparation systems were compared over the 1973–1974 spring-summer season on a pseudogleyed “Tokomaru” silt loam, on two adjacent experimental sites. Experiment 1 was tilled and left fallow over the winter of 1973, while experiment 2 was left in pasture over the winter. Both areas were then prepared and sown with choumoellier seed by one of the following systems: 1. (1) traditional plough/disc/harrow, sown with conventional field drill; 2. (2) rotary-cultivation, sown with conventional field drill; 3. (3) zero tillage (or direct drilling) after herbicide application (paraquat and Dicamba). As a result of these treatments, the soil which had been sprayed with herbicide and direct-drilled was significantly more resistant to structural damage than the other two treatments as determined by sieving under water. Soil structural stability under the rotary cultivated treatment appeared to decrease to a greater extent than with tillage based on ploughing, as the length of time out of pasture increased. Dry-sieving of soil sample confirmed these effects. The rotary cultivation treatment resulted in the greatest proportion of soil in the smaller aggregate size fraction (less than 1·7 mm dia.) at all sampling dates. The results suggest that the wider use of zero tillage (or direct drilling) techniques and machinery may result in more desirable soil structure being retained under intensive cropping situations.