Benefits of increased soil exploration by wheat roots

Increased subsoil water extraction by wheat roots enhanced through management or breeding can increase yield, but the benefits depend on the seasonal pattern of water availability as influenced by rainfall distribution, soil type and management. We used a well validated crop simulation model to assess the wheat yield benefits arising from 20% faster root descent and/or more effective water extraction in the subsoil (>0.6 m) under different management scenarios. The analysis was conducted in Mediterranean, temperate equi-seasonal and subtropical Australian wheat-growing environments on deep sand, loam and deep clay soils, respectively.Overall mean yield benefits of 0.3–0.4 t ha−1 were predicted from the combination of faster descent and more efficient roots at all sites and yield reductions were rare, although considerable seasonal and site variation in yield benefits was evident (range in benefits −0.1 to 1.4 t ha−1). In general, faster root descent provided less separate benefit to water uptake and yield (up to 9 mm and 0.1 t ha−1) than more efficient subsoil extraction (up to 21 mm and 0.3 t ha−1), especially for optimal sowing dates, although late-sown crops on deep sands were an exception. At all sites, the yield impacts of preceding management (0.5 to 1.8 t ha−1) and sowing date (0.1 to 0.9 t ha−1) were more consistent and often exceeded or overrode those of root modification by influencing the depth of profile wetting and duration of root descent. For example there was little benefit (<0.1 t ha−1) of modified roots following lucerne compared to an annual crop at most sites as the soils rewet below 1 m less frequently. The study provides insights for targeting those environments and management scenarios for which the largest yield benefits will arise from investments to improve wheat root systems.

► Mean yield benefits of 0.3–0.4 t/ha were simulated for modified root systems
► Seasonal and site variation in yield benefits was large
► Impacts of agronomic management on yield often exceeded those of root modification.