Factors Influencing Soil Structural Stability within a Growing Season

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Abstract
Temporal fluctuations in soil structural stability within cropping treatments are often as large as differences between crops during the growing season. The relative importance of soil moisture, roots, and microbial biomass as factors contributing to this variation were investigated. Research was conducted on a fine‐silty, mixed, mesic Typic Eutrochrept intergrading to a fine‐silty, mixed, mesic Typic Haplaquept soil near Elora, ON. Six perennial forage treatments, established 2 yr previously, were compared with spring‐seeded conventional and zero‐till corn (Zea mays L.). The plow layer of each cropping treatment was sampled at monthly intervals. A combination of wet sieving and turbidimetry was used to provide a rapid assessment of wet aggregate stability (WAS) and dispersible clay (DC), respectively. On average, the forages had significantly less DC and greater WAS than the two corn treatments. Structural stability was found to decrease with increasing soil water content (r = 0.80 for DC and r = 0.74 for Was, both significant at P = 0.01). The corn soil experienced less extreme drying in the spring. Stepwise multiple‐regression analyses selected soil moisture and microbial biomass (in that order) as significant predictors of structural stability within the growing season. Using both parameters, it was possible to explain up to 85% of the temporal variation in DC and WAS on a by‐treatment basis.