Grain production is a key pillar in Australia's economy but it operates within challenging climatic and edaphic environments, with unreliable and often low rainfall. Moreover many of the production landscapes have soils which have limited capacity to store water or have a range of physical, chemical or biological constraints. High soil strength has emerged as an increasing problem. Strategic deep tillage approaches (>= 30 cm) are being deployed by many farmers with significant (>50%) yield responses. However the specific mechanisms under-pinning the yield responses to deep tillage are not yet clear. Our hypothesis was that the primary response by cereal crops to deep tillage is an increase in soil water use (evapotranspiration), leading to increased grain yield. Secondly, we postulated that improved access to deep soil water following deep tillage would be reflected through an increase in grain size. Five field experiments were established across four sandy soil sites in a strongly water limited environment, with a range of tillage interventions and nutrition supplements. Measurements of crop water use, grain yield and yield components were made for three or four years post treatment. Crops responded much more to deep tillage (-15 to 100%, mean 50%) than to crop nutrition interventions (0 - 62%, mean 7%). Increases in crop water use (evapotranspiration) were modest or not evident and generally insuffi-cient to explain the magnitude of yield responses. Increased crop transpiration, ear density (n/m2) and grain number per ear contributed most to yield increases. Increased crop water use does not appear to be the main driver of grain yield responses to deep tillage in this environment, rather pre-anthesis effects on crop develop-ment, radiation interception and transpiration appear to result from direct effects of soil strength on crop tillering caused by hormonal responses, which are now beginning to be understood.