A method for studying the effects of soil aggregate size and density

Soil macroproperties, such as bulk density, porosity, water conductivity, and aeration, have been utilized in order to evaluate soil structure effects on crop yields. It has been suggested that many of the limitations to crop growth can be explained by the physical properties of the aggregates. To explore some aspects of this, a method to simulate soil aggregates of different sizes and densities was developed and tested. A Collamer silt loam soil (fine-silty, mixed, mesic Glossoboric Hapludalf) was dried, crushed, sieved, and compressed to different densities (1.4, 1.6, and 1.8 Mg m(-3)). The resulting 25- and 50-mm-thick cylindrical soil slices were cut to two different cubical sizes (25- and 50-mm sides). Cylinders with continuous horizontal and vertical macropores were assembled from these artificial aggregates to make six different treatment combinations of aggregate size and density. Corn (Zea mays L.) seedlings were transplanted into the cylinders and grown in a growth chamber for 27 d. Results show that high aggregate density limits crop growth and that, at intermediate densities, aggregate size assumes more significance as a limiting factor.