An assessment of the vulnerability of soil structure to destabilisation during tillage. Part II. Field trials

Abstract

Tillage operations were conducted on a Calcareous Pelosol over a range of soil water contents and at differing tillage intensities, using both a mouldboard plough and a rotary cultivator. Measurements were made of the tillage specific energy requirements and tests were made to assess subsequent aggregate disruption by measuring the quantity of mechanically-dispersible clay. The rotary cultivator had a specific energy requirement between three and four times that recorded for the plough and both implements showed a consistent increase in energy requirement as soil water contents declined towards the soil plastic limit. Aggregates collected following tillage yielded greater amounts of dispersed clay than those collected immediately prior to tillage, with differences increasing with soil water content, but differences were not significant at and below the plastic limit. Aggregates collected following rotary cultivation yielded larger amounts of dispersed clay than those collected following ploughing, at a given soil water content. The results of the field experiments were in good agreement with predictions of laboratory rests reported in Part I, in which the quantity of clay dispersed was related to soil water content and the specific energy of disruption. The three soils cultivated showed large differences in their sensitivity to disruption measured in terms of the quantity of mechanically-dispersible clay. Aggregates collected and dried following tillage had a greater tensile strength than aggregates collected immediately prior to tillage. The water content at the time of collection was also shown to influence aggregate strength. Aggregate strength was found to correlate with the quantity of clay dispersed.