Corn root growth in soil columns with artificially constructed aggregates

Soil structure, defined as the size and density of aggregates, has been recognized as an important indicator of potential soil productivity. To better understand the impact of inherent root-soil interaction effects on soil productivity, we evaluated root growth in soils with known structure. Corn (Zea mays L.) seedlings were grown for 33 d in soil columns, with Collamer silt loam soil (Fine-silty, mixed, mesic Glossaquic Hapludalf), that was artificially manipulated to create cubical aggregates of different sizes (25 and 50 mm, on each edge) and densities (1.4, 1.6, and 1.8 Mg m(-3)). Plant response was characterized by root and shoot growth. Root length, diameter, and weight were measured in zones within aggregates (intraaggregate pores, or micropores), and between aggregates and between horizontal slices of soil (collectively, interaggregate pores, or macropores). The preferred root growth pathway (within micropores or within macropores) differed with aggregate density and was influenced by aggregate size. Length of roots penetrating aggregates decreased exponentially with increasing aggregate density. Root growth (length) also shifted from within micropores to within macropores with increasing aggregate size, suggesting an interaction effect between density and size of aggregates. Accurate assessment of this interaction may allow the determination of the optimum conditions for root growth and, consequently, the maximum potential for crop growth in a specific soil.