Annals of Botany

• Background and Aims The impedance to root growth imposed by soil can be decreased by both mucilage secretion and the sloughing of border cells from the root cap. The aim of this study is to quantify the contribution of these two factors for maize root growth in compact soil.

• Methods These effects were evaluated by assessing growth after removing both mucilage (treatment I - intact) and the root cap (treatment D - decapped) from the root tip, and then by adding back 2 µL of mucilage to both intact (treatment IM - intact plus mucilage) and decapped (treatment DM - decapped plus mucilage) roots. Roots were grown in either loose (0·9 Mg m^-3) or compact (1·5 Mg m^-3) loamy sand soils. Also examined were the effects of decapping on root penetration resistance at three soil bulk densities (1·3, 1·4 and 1·5 Mg m^-3).

• Key Results In treatment I, mucilage was visible 12 h after transplanting to the compact soil. The decapping and mucilage treatments affected neither the root elongation nor the root widening rates when the plants were grown in loose soil for 12 h. Root growth pressures of seminal axes in D, DM, I and IM treatments were 0·328, 0·288, 0·272 and 0·222 MPa, respectively, when the roots were grown in compact soil (1·5 Mg m^-3 density; 1·59 MPa penetrometer resistance).

• Conclusions The contributions of mucilage and presence of the intact root cap without mucilage to the lubricating effect of root cap (percentage decrease in root penetration resistance caused by decapping) were 43% and 58%, respectively. The lubricating effect of the root cap was about 30% and unaffected by the degree of soil compaction (for penetrometer resistances of 0·52, 1·20 and 1·59 MPa).