Genotypic advantages of root–shoot growth alleviate the grain yield reduction of maize (Zea mays L.) under various soil compaction levels

Soil compaction has become a serious limitation for further increasing the grain yield of maize (Zea mays L.) in the North China Plain (NCP). However, considerable variability exists among maize hybrids in their grain yield responses to soil compaction. To understand the physiological processes related to the variation of responses among maize hybrids to different soil compaction levels, a two-year field experiment was conducted with 17 maize hybrids and three soil compaction treatments (NC, no compaction with soil bulk density (SBD) of 1.0–1.3 g cm^–3; MC, moderate compaction with SBD of 1.4–1.5 g cm^–3, and HC, heavy compaction with SBD>1.6 g cm^–3) to examine the root and shoot morphological traits, dry matter accumulation, and grain yield. Compared to NC, MC and HC significantly reduced the maize yield by 0.9–26.7% and 5.9–41.1% across the hybrids and years, respectively. Hybrids with high compaction tolerance (H) had greater grain yield than those with middle compaction tolerance (M) and low compaction tolerance (L), particularly under HC. The yield benefits obtained from the H hybrid were enhanced due to better root and shoot growth under HC conditions. Greater root length, root surface area, and root weight, as well as root activity, absorption capacity, and antioxidant capacity for H hybrid was found under HC conditions, and it also showed increased leaf area index and dry matter accumulation. Moreover, the increases in root growth indices for the H hybrid were greater than that of shoot growth, particularly under HC conditions, leading to a greater root/shoot ratio. We conclude that soil compaction impacts maize root and shoot growth differently depending on genotype, and the root growth advantages of the H hybrid were more obvious than shoot growth, which enhanced the yield benefits from the H hybrid under heavy compaction conditions.