Corn root growth in soil columns with artificially constructed aggregates

Soil structure, defined as the size and density of aggregates, has been rec ognized as an important indicator of potential soil productivity. To better understand the impact of inherent root-soil interaction effects on soil pr oductivity, we evaluated root growth in soils with known structure. Corn (Z ea mays L.) seedlings were grown for 33 d in soil columns, with Collamer si lt loam soil (Fine-silty, mixed, mesic Glossaquic Hapludalf), that was arti ficially manipulated to create cubical aggregates of different sizes (25 an d 50 mm, on each edge) and densities (1.4, 1.6, and 1.8 Mg m(-3)). Plant re sponse was characterized by root and shoot growth. Root length, diameter, a nd weight were measured in zones within aggregates (intraaggregate pores, o r micropores), and between aggregates and between horizontal slices of soil (collectively, interaggregate pores, or macropores). The preferred root gr owth pathway (within micropores or within macropores) differed with aggrega te density and was influenced by aggregate size. Length of roots penetratin g aggregates decreased exponentially with increasing aggregate density. Roo t growth (length) also shifted from within micropores to within macropores with increasing aggregate size, suggesting an interaction effect between de nsity and size of aggregates. Accurate assessment of this interaction may a llow the determination of the optimum conditions for root growth and, conse quently, the maximum potential for crop growth in a specific soil.