ROOT-SOIL CONTACT OF MAIZE, AS MEASURED BY A THIN-SECTION TECHNIQUE .2. EFFECTS OF SOIL COMPACTION

The degree of root-soil contact was evaluated from thin sections for maize grown in pots with soil aggregates packed at three bulk densities. Root-soil contact was found to increase with bulk density of the soil. For soils with a porosity of 60, 51 and 44% (v/v), the average fraction of root-soil contact was 60, 72 and 87%, respectively. The frequency distribution of nearest-neighbour distances from points in a void to the nearest point of the soil matrix was measured. This was then used for a statistical test of a null hypothesis of random positioning of roots in voids. Where roots grew in larger pores or voids the degree of root-soil contact was greater than expected for random positioning of roots. Possible mechanisms of the observed preference of roots for proximity to the soil, and higher root-soil contact are discussed.