A METHOD FOR STUDYING THE EFFECTS OF SOIL AGGREGATE SIZE AND DENSITY

Soil macroproperties, such as bulk density, porosity, water conductivi ty, and aeration, have been utilized in order to evaluate soil structu re effects on crop yields. It has been suggested that many of the limi tations 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 tes ted. A Collamer silt loam soil (fine-silty, mixed, mesic Glossoboric H apludalf) was dried, crushed, sieved, and compressed to different dens ities (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- a nd 50-mm sides). Cylinders with continuous horizontal and vertical mac ropores were assembled from these artificial aggregates to make six di fferent treatment combinations of aggregate size and density. Corn (Ze a mays L.) seedlings were transplanted into the cylinders and grown in a growth chamber for 27 d. Results show that high aggregate density l imits crop growth and that, at intermediate densities, aggregate size assumes more significance as a limiting factor.