Factors affecting seedbed properties of cracking clay soils of the Darling Downs

Abstract

Eleven clay soils were sampled on the Darling Downs, Queensland. Five of the soils (group a) rarely exhibit poor wheat seedling emergence, but emergence problems are common in the remaining six soils (group b). The dry aggregate size distribution of prepared seedbeds was measured along with a number of basic soil characteristics. The modal aggregate size in both groups is 5-2 mm, but in group (a) sizes <2 mm are favoured as against aggregates >5 mm, whereas the reverse is true for group (b). These trends represent a natural characteristic of the groups, and are not the result of cultivation practices. The geometric mean size of dry aggregates of the two groups is significantly different as is the electrical conductivity of 1:1 soil:water suspensions. The possible causality of these soil properties is discussed, but no satistactory explanation is proposed.