Soil compaction development facilitated the decadal improvement of the root system architecture and rhizosheath soil traits of soybean in the North China Plain

Machinery agriculture has increased crop yield but induced soil compaction worldwide in the last decades. The crop yield increase is partly attributed to high-yielding crop breeding, but the effects of emerging soil compaction on the selection of root system traits and its impact on yield increase remain unclear. The objectives of this study were 1) to identify the effects of soil compaction on grain yield and root system architecture and rhizosheath soil traits of soybean (Glycine max (L.) Merr.) at the full-bloom stage, 2) to understand whether and how the development of soil compaction affected the selection of merit root and rhizosheath soil traits through crop breeding and contributed to soybean grain yield increase. Thirty-four most popular soybean cultivars released before and after the wide use of agricultural machinery in the North China Plain were grown in the fields without (NOM) and with (COM) applied soil compaction in 2017 and 2018. The phenotypes of root system, including rhizosheath soil, of soybean, were separated by soil compaction and cultivar release period, confirming the development of soil compaction and its impacts on the co-development of rhizosheaths with the root system of soybean. The correlation with the year of release of the cultivar demonstrated that 21 out of the 24 measured traits were selected by crop breeding. Multivariate analysis of the variance demonstrated that the selection of thinner hypocotyl, more root tips, and denser rhizosheath soil were relevant to the soil compaction development. The selection of shorter plant height, larger root biomass and area, thinner root tip, thicker taproot, and rhizosheath soil mass were likely relevant to the experimental year factor caused by drought or its associated change in nutrient availability. Most of the selected traits increased the resistance or the resilience to soil compaction and nine of them correlated with the grain yield of cultivars released at different periods. These results for the first time suggested that crop breeding increased grain yield partly by increasing the resistance and resilience to soil compaction. Soil compaction could be considered in a future breeding program design to increase crop breeding efficiency by selecting resistant and resilient root traits.