Results

Growth response to early sowing under field conditions

To study the impact of sowing date on sunflower development\sout, we performed two field experiments with different sowing dates in 2021 and 2022. The pattern of plant and canopy growth differed between ES and normal sowing (Fig. 2). Although the growth rate of the canopy cover did not differ with ES (Fig. 2E), the latent phase was ca. 25 days longer (60 d, vs. 35 d with normal sowing). This was consistent with lower vigor (i.e., plant emergence) in the cold treatment (Fig. 2A) and the observation that the number of days required for leaves to fully develop was nearly twice as long with ES (45 d) than with normal sowing (25 d) (Figure 2D). Once emerged, plants grew significantly slower with ES (1.4 cm/d) (Fig. 2C) than with normal sowing (2.2 cm/d) (Fig. 2F).