In‐row soil aggregate characteristics for two Iowa soils

Chemical and physical characteristics of soil aggregates from Clarion loam (fine‐loamy, mixed, mesic Typical Hapludoll) and Edina silt loam (fine, montmorillonitic, mesic Typic Argialboll) soil were evaluated to compare two alternate farming practices. Aggregate size distribution was measured for the 0‐to‐3 mm and 0‐to‐76 mm fractions collected from within existing ridges to a soil depth of 0.15 m prior to planting corn (Zea mays L.), after the first cultivation, at anthesis, and after harvest in 1990. Selected physical and chemical properties were determined for air‐dry aggregates in six size classes (0‐to‐0.5, 0.5‐to‐1.0, 1.0‐to‐2.0, 2.0‐to‐3.0, 3.0‐to‐4.0, and 4.0‐to‐5.0 mm) collected from the two Iowa soils prior to planting. Temporal changes in aggregate size distribution were observed for both soils, presumably because of combined rainfall and crop management effects. Physical and chemical properties of soil aggregates showed large differences between locations and within size fractions when compared to the bulk soil. Clarion loam had relatively more consistent exchangeable cation concentrations compared to Edina silt loam, presumably because of sustained incorporation of manure and municipal sludge at that site. Soil aggregation and aggregate properties can be used as indicators to evaluate the effects of alternate fanning practices.