Placing seeds with the embryo pointed down improves deep root growth in winter wheat under soil compaction stress.

Background: A strong root penetration ability is beneficial for mitigating soil compaction stress. Seed orientation affects root growth and seedling vigor, but its effects on root penetration ability are unknown. Methods: Four seed orientations in winter wheat (Triticum aestivum L.) were created in different pot experiments: embryo pointed down (Embryo-down), embryo pointed up, lying flat with the crease down and lying flat with the crease up. A thin wax layer in a small soil pot was used to simulate soil compaction, and different levels of soil bulk density (1.4 and 1.7 g cm−3) at 20–40 cm, combined with two water regimes, were set up in a large soil tube experiment. Results: In sand pot experiment, the Embryo-down treatment resulted in a greater seminal root growth angle and root length than the other three orientations. Surprisingly, the Embryo-down treatment exhibited a greater root penetration ability, which was proven by the greater deep root mass density in both the small soil pot with thin wax layer and the large soil tube under the high compaction level of 1.7 g cm−3. The larger deep root system under Embryo-down enhanced the soil water uptake ability, as evidenced by either greater soil water depletion or a cooler canopy temperature. As a result, the Embryo-down treatment produced the highest grain yield with a 42% increase under full irrigation and a 19% increase under no irrigation. Conclusions: Placing the seeds with the Embryo-down can improve deep root growth and grain yield in winter wheat under soil compaction stress. [ABSTRACT FROM AUTHOR]