THE RESISTANCE EXPERIENCED BY ROOTS GROWING IN A PRESSURIZED CELL - A REAPPRAISAL

Resistance to root growth in the original flexible-sided cells used by Goss (1977) to study the effect of mechanical impedance on root growth was estimated by two methods. Firstly, the resistance to pushing a 2-mm diameter 30° semiangle metal probe into the cells containing either saturated ballotini, or air-dry or saturated sand was measured. Secondly, the pressure required to inflate a 3-mm diameter thin walled latex tube was measured in the cells. Penetrometer resistance was more than forty times greater than the pressure applied externally to the cell. The pressure required for tube inflation was highly dependent on the experimental procedure followed, but the pressure required to inflate an initially deflated tube exceeded the externally applied pressure by a factor of between 5 and 9 times. These findings suggest that it is necessary to reinterpret the results of many root growth experiments designed to quantify the effects of mechanical impedance on root growth rates and performed in similar cells, and have implications for the future conduct and interpretation of such experiments. © 1990 Kluwer Academic Publishers.