A significant proportion of arable land is prone to soil physical constraint, from texture contrast, from formation of hardpans, or from increase in soil strength on drying, all of which limit root exploration and thus access to nutrients and water for plant growth. We validated a wax layer system to simulate a compaction layer in a soil column, noted it allowed experimental separation of soil water and soil strength as constraints, and showed an overall agreement in genotype ranking with field soils. Forty diverse wheat cultivars were then screened for hardpan penetration ability against wax layers in soil columns, with validation by maximum root depth in contrasting field soils. Roots penetrating to depth were able to access additional soil water below the hardpan. A DHL population was screened and QTLs were identified which were associated with penetration of the wax layer, and with deeper roots in the field. Pattern analysis identified, however, that different root traits were needed in different soil conditions. Penetration ability was expressed only in the presence of soil physical constraint, and was only of benefit when extra resources were available for capture from deeper soil layers, and in turn, if the extra growth was expressed as additional grain yield. This comprehensive approach is essential, as success from trait inclusion requires an effective systems design, so adapted plants with extra traits are able to deliver in appropriate soil conditions. Understanding is needed at various levels in the plant and the system across many disciplines.