Water-stable aggregates and their organic carbon distribution after five years of chemical fertilizer and manure treatments on eroded farmland of Chinese Mollisols

Sui, Y.-y., Jiao, X.-g., Liu, X.-b., Zhang, X.-y. and Ding, G.-w. 2012. Water-stable aggregates and their organic carbon distribution after five years of chemical fertilizer and manure treatments on eroded farmland of Chinese Mollisols. Can. J. Soil Sci. 92: 551-557. Water-stable aggregates are the foundation for both water and fertility conservation and nutrient release in the soil. We investigated the effects of 5 yr of different fertilizer treatments (chemical fertilizer and fertilizer +manure) on water-stable aggregates and their organic carbon distribution patterns within five different simulated erosion levels (removal of 0, 5, 10, 20, and 30 cm of topsoil) in an eroded Black soil of northeast China. Water-stable aggregates greater than 0.25 mm in size and aggregate-associated-carbon (AAC) contents in the aggregates were greater in the soils with fertilizer + manure application than those with chemical fertilizers alone. Both water-stable aggregates and AAC contents declined (P<0.05) gradually as soil removal depth increased. The decline in aggregates larger than 1 mm with increased erosion depth was greater in the fertilizer-only application than that in the fertilizer + manure application. The minimum value was found in the case of 30 cm topsoil removal under the fertilizer-only application. Significant correlations (P < 0.05) between water-stable aggregates greater than 1 mm and soil organic carbon (SOC) were observed in the soil with fertilizer +manure application. A significant positive correlation was observed between SOC and all different aggregate classes with both chemical fertilizer and fertilizer +manure applications. AAC within large aggregates and SOC contents were significantly higher in the fertilizer +manure treatment than in the fertilizer-only treatment. The study shows that water-stable aggregates (>1 mm) can be used as an indicator in evaluating the influence of carbon transformation on soil quality. The increases in SOC by cattle manure application to eroded Black soil might be responsible for the larger size aggregate formation.