Timing and conditions modify the effect of structure liming on clay soil

Two dates (early, normal) for application and incorporation of structure lime to clay soil were examined at four field sites, to test whether early liming had more favourable effects on aggregate stability. Aggregate size distribution measurements revealed a finer tilth at the early liming date (20 August) than the normal date (14 September). Aggregate stability estimated one year later, using as a proxy turbidity in leachate from 2–5 mm aggregates subjected to two simulated rainfall events, was significantly improved (11% lower turbidity) with early compared with normal liming date. Three years after structure liming, soil structural stability measurements on lysimeters (15 cm high, inner diameter 18 cm) subjected to repeated simulated rainfall events showed no significant differences in turbidity in leachate between the early and normal liming dates. However, there was a strong interaction between liming date and site indicating different reactions at different sites. Our results suggest that early spreading and incorporation can improve the success of structure liming, but only if soil conditions are favourable.