The influence of mechanical resistance and soil water on the growth of seminal roots of maize

n a pot experiment, the soil resistance and soil water potential were varied independently and the effects on seminal root growth quantified. Because evapotranspiration was prevented, the soil water status was constant. Under the prevailing growth conditions the growth rate without me- chanical or osmotic constraints was 48 mm day- ~ for a primary root and 32 mm day- ~ for an adventitious seminal root. However, root growth was completely inhibited in a soil with a pene- trometer resistance of 4.2 MPa and a soil water potential of - 1.7 MPa. Between a resistance of 0 and 0.1 MPa, the roots appeared to be more sensitive to mechanical or osmotic constraints than at higher levels of soil strength, which is attributed to changes in cell wall structure induced at low mechanical resistance.