Soil aggregate stability and organic carbon after a decade of cropping system diversification

Diversified cropping systems can alter various rhizosphere properties over time. We examined soil aggregate stability and organic carbon status in a cropping sequence experiment initiated in 2013 at Beaverlodge Research Farm, Alberta. Eight different cropping sequences comprising two perennial legumes (red clover and alsike clover), three perennial grasses (timothy, meadow bromegrass, and creeping red fescue), and four annual crops (wheat, canola, pea, and barley) were evaluated under three levels of nitrogen (0, 45, and 90 kg N/ha) application. After ten years of experimentation, soil samples were collected from 0-15cm depth at post-harvest in 2023. The aggregate stability and size distribution were analyzed following the modified Yoder method, and the organic carbon was determined using the dry combustion method. Soil aggregate stability was calculated as the sum of the percentage of soil on each sieve (4, 2, 1, 0.5, 0.25, and 0.125 mm) and expressed as mean weight diameter (MWD). The results showed that the cropping sequence that contained creeping red fescue in six out of ten crop years, had a higher MWD in comparison to other sequences. The higher MWD was associated with a higher proportion of large-sized aggregates (1-4mm) and fewer small-sized aggregates (<0.25mm). For the intermediate aggregates size class (0.25-1mm) and organic carbon, perennial forage-based sequences exhibited statistically comparable results with annual cropping sequences. Results indicate that long-term diversifying cropping systems with perennial forage can improve soil quality and support sustainable agriculture.