Effect of plant species, nitrogen fertilizer and grass age on the dynamics of intra-aggregate SOM

Plant wax compounds (n-alkanes and alcohols) were used to trace C from the dominant pasture species to different water-stable aggregate (WSA) size classes to investigate if changes in the plant community composition caused by grass ley age and N amendment were reflected in the dynamics of intra-aggregate SOM. Age of the ley influenced the formation of aggregates, and fertilizer N application decreased %C and %N of the macroaggregates. Although changes in the plant community composition due to N amendment and ley age were reflected in the concentrations of plant wax compounds in the different WSA classes, the results of this study are more indicative of the direct effect of N fertilizer, than of the effect of dominant plant species, on intra-aggregate OM dynamics. The results of this study were found to support the suggestion that N amendments increase intra-aggregate OM dynamics especially in the smaller WSA size classes.