Distribution of β-Glucosidase Activity within Aggregates of a Soil Amended with Organic Fertilizers

Problem statement: Distribution pattern of enzyme activities in soil aggregate size classes as affected by organic amendments is not well understood. Approach: A study was conducted to evaluate the effects of repeated annual application of Cow Manure (CM), Sewage Sludge (SS) and Municipal Solid Waste Compost (MSW) on the distribution of β-Glucosidase (βG) activity within aggregates of a soil. Soil samples were collected from 0-15 cm of a soil which, had been treated annually from 1999-2006 at 4 application rates with three replications. A control (with no application) was also run. Soil organic C content and βG activity were measured in 5 aggregate size fractions. Results: Results illustrated that application of the amendments decreased the proportion of microaggregates (<0.25 mm). The proportion ranged from 64% in control to 35% in MSW. In contrast, the proportion of macroaggregates (>0.25 mm diameter) enhanced from 35% in control to 65% in MSW. Application of organic amendments modified the distribution of Soil Organic C (SOC) content and βG activity. Distribution of SOC in macroaggregate classes was not identical in CM, SS and MSW treatments. The distribution pattern of βG activities in aggregate size classes was dissimilar to those of SOC contents. In general, an increasing trend was observed in βG activity as the aggregate sizes increased. The highest level of βG activity was observed in aggregate size classes of >2 mm of all applied soils. Among the solid waste treatments, CM induced greater βG activity in macroaggregates. For all aggregate size classes, the lowest level of βG activity was observed in control. Conclusion/Recommendations: To conclude, organic fertilization increased the proportion of macroaggregates to microaggregates. The highest activities of βG and SOC contents were observed in macroaggregates and in soils received the highest rates of organic fertilizer applications.