Response of Canola and Cereals to Amendment of Subsurface Soil Acidity and a Hardpan

Context Limitations to crop yield due to subsurface (5–15 cm depth) compaction layers (>2 MPa) and subsurface acidity (pHCa <4.8) have frequently been reported on the non-sodic soils of south-eastern Australia, but amendment studies have been limited in number and inconsistent in the extent and longevity of any response. Aim We tested the hypothesis that amendment of subsurface acidity and compaction would lead to increased grain yield. Method We investigated crop response to the alleviation of these combined subsurface soil constraints by using deep ripping and dry limestone injection to 30 cm depth over 3 years in a canola–cereal sequence. Key results Deep tillage and injection of limestone into the soil both failed to produce significant grain yield responses in any year, despite the reduction of soil strength and increase in pH in subsurface layers. Early vegetative growth sometimes responded to the treatments, but the loss of stored soil water during drier than average seasons appeared to limit grain response. However, we also observed that a proportion of plant roots penetrated these relatively thin constraint layers in unamended soils. Conclusions Amelioration of subsurface acidity and compaction does not necessarily increase grain yield. Implications The effects of subsurface acidity and compaction should be tested on other species and during varying rainfall deciles. Given the potentially large resource requirements for deep amendment of soils, we propose that the selection of tolerant species and cultivars might be more effective in the short term.