In this opinion article we examine the relationship between penetrometer resistance and soil depth in the field. Assuming that root growth is inhibited at penetrometer resistances > 2.5 MPa, we conclude that in most circumstances the increases in penetrometer resistance with depth are sufficiently great to confine most deep roots to elongating in existing structural pores. We suggest that deep rooting is more likely related to the interaction between root architecture and soil structure than it is to the ability of a root to deform strong soil. Although the ability of roots to deform strong soil is an important trait, we propose it is more closely related to root exploration of surface layers than deep rooting.
HighlightsWe present evidence to support the hypothesis that the general and well-documented shape of the relationship between root length density and soil depth in UK grown winter wheat is related to the increase in soil strength with depth.Effects of the soil environment on root length distribution were greater than genetic effects and this was most likely related to soil saturation.In a dry season, there was genotypic variation in rooting depth.Greater root length at depth in the dwarf NILs suggests that deep rooting is not simply related to plant height.
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