Dual-purpose wheat systems—where crops are grazed during vegetative stages and later harvested for grain—offer flexibility in mixed farming, particularly under variable rainfall. However, the effects of grazing-induced defoliation on root development, plant water status, stress response and final grain yield have been underexplored, especially under multi-season field conditions. We hypothesized that grazing-induced defoliation would temporarily suppress root growth but conserve subsoil water through reduced transpiration, potentially alleviating terminal drought stress to improve yield in dry seasons, although outcomes would be season-dependent. The study aimed to quantify the effects of grazing (defoliation) on root growth dynamics, soil water availability, canopy thermal stress responses, and grain yield of early-sown winter wheat across variable field seasons Field experiments were conducted over three growing seasons (2021–2023) in southern Australia using paired grazed and un-grazed treatments in early-sown winter wheat. Root depth progression and root length density were monitored throughout the season, together with soil moisture profiles, canopy temperature, and yield components. Seasonal conditions ranged from relatively wet (2021–2022) to dry (2023), enabling assessment across contrasting water availability scenarios. Grazing consistently delayed root descent by ∼200°C days but root depth had generally recovered by anthesis, with only transient reduction in root length density (0.4–0.8 m). In the dry 2023 season, grazed crops conserved subsoil water, lowered canopy temperatures, and reduced grain-filling stress, while effects were minimal in wetter years. Despite more rapid regrowth during the critical period, grazed crops had consistently lower yield (-0.6 t ha⁻¹), likely due to more biomass allocation to leaf and stem and delayed phenology. Grazing caused significant but transient changes in root growth and water use which had no effect on grain yield, which was primarily affected by post-grazing shoot regrowth dynamics. Grazing related stress reduction during spring drought did not translate into yield gains. These results improve mechanistic understanding of dual-purpose wheat systems and provide parameters to better represent post-defoliation root growth and water-use dynamics for use in crop models under variable climates. • Grazing delayed root descent by ∼200°C days, with full recovery by anthesis and no lasting rooting constraints. • Temporary reductions in root length density (0.4–0.8 m) had minimal long-term effects on water access. • In dry conditions, grazed crops conserved subsoil water and reduced canopy temperatures during grain filling. • A consistent yield penalty (∼0.6 t ha⁻¹) was linked to delayed phenology and shoot regrowth rather than root limitation.
Han et al. (Mon,) studied this question.