LAUSR

Abstract The seed emergence and yield of rainfed rapeseed ( Brassica napus L.) are commonly limited by soil water availability during the growing season. The return of straw to the field helps maintain soil moisture status, but can cause long hypocotyls of seedlings and result in yield reduction. Using the swede rape hybrid Huayouza 62 as material, the effects of sowing depth and soil compaction on seedling growth and yield under conditions of straw return to the field were investigated. The bulk density and water content for the soil layers of 0–10 and 10–20 cm significantly increased and total porosity decreased under the compaction of shallow (2 cm) and deep sowing (3 cm), and the effect was greater for the 0–10 cm layer. Without soil compaction, the seedling emergence rate was substantially improved with increased sowing depth, but was dramatically decreased in the case of compacted soil. The soil compaction significantly elevated the seedling emergence rate with shallow sowing, and increases were 15.57 and 17.08% for 2013–2014 and 2014–2015, respectively; however, with deep sowing, compaction had no significant effect. The variation in seedling density was consistent with that of the seedling emergence rate. Compared to shallow sowing, deep sowing induced a thinner rapeseed stem, but soil compaction had an opposite effect. Increasing the sowing depth or soil compaction improved the overall yield by elevating the root/shoot ratio of seedlings and lodging resistance, effectively eliminating weed infestation. Significant interactions were found between sowing depth and soil compaction in yield and siliques. Shallow sowing with soil compaction had a positive effect on growth and development, and dramatically increased seedling density and siliques, leading to improved yield.