Root Growth Through Porous Media Under Controlled Conditions: I. Effect of Pore Size and Rigidity

The effect of rigid and nonrigid glass bead systems with six different pore diameters on growth of maize ( Zea mays L.) seedlings was determined. Maize seedlings were grown for 14 days in specially constructed cells which permitted development of rigidity in the bead matrix by a clamping device and allowed for aeration with compressed air. The data indicated a definite influence on root growth of both the rigidity of the system and the size of the pores present in the system. Maize roots did not grow into rigid porous systems which had pore diameters smaller than approximately 138µ and in rigid systems any reduction in pore diameter below approximately 412µ resulted in some reduction in root growth. However, maize roots were found to grow approximately the same in all nonrigid bead systems, regardless of the size of the pores. Relating this information to natural soil conditions suggests that under field conditions, plant roots generally do not grow through existing pore space but extend through the soil only due to their ability to displace the soil particles and create their own path through the soil.