SECONDARY TILLAGE TOOL EFFECT ON SOIL AGGREGATION
A field experiment was conducted to study effect of tillage tool type on soil aggregation and soil aggregate properties when tillage was done over a range of soil moisture contents. Tillage with a tandem disk harrow and C-shank field cultivator was done at moisture contents from 12.8 to 21% dry-weight basis. Aggregate size was determined by computing mean-weight-diameter by use of a rotary sieve. Aggregate-mechanical-stability, defined as the difference between mean-weight-diameters after and before a drop shatter treatment and normalized by dividing by initial mean-weight-diameter, was used to evaluate stability of aggregates formed by tillage. Aggregate strength was determined by maximum force and energy needed to crush individual aggregates. Though data were variable, tillage with a tandem disk harrow tended to produce larger and stronger soil aggregates than did tillage with a C-shank field cultivator. Aggregates formed by tillage at a moisture content greater than the lower plastic limit were larger and required greater force to crush than did aggregates formed at lower moisture contents.