Testing the Effect of a Microbial-Based Soil Amendment on Aggregate Stability and Erodibility.

Minimizing soil erosion is essential for maintaining proper soil quality and thus preserving soil productivity. The erodibility of a soil is closely linked to its structural stability as well as its infiltrability. This study focuses on testing the effect of two different soil amendments on soil aggregate stability and erodibility. Two commercial products, gypsum and a microbial-based solution were used for the experiment and were tested on two Danish sandy loamy soils as well on a sandy soil from Tanzania. The carrier of the microbial-based product, a glycerol solution, was tested as well.  In the laboratory, soils were treated with the soil amendments in a two-step procedure at controlled water contents following aerobic incubation in closed containers. Water-aggregate stability and clay dispersion were measured on soil aggregates less than 8 mm in diameter. Aggregate stability was measured on a Yoder-type wet sieving apparatus whereas clay dispersion was measured on and end-over-end shaking device where artificial rainwater solution was added to the soil. I addition, a rainfall-runoff experiment was done on square flumes where runoff from the flumes was collected during a four hour rainfall simulation. Here only the microbial-based product was tested together with a control. Results showed that in general the microbial-based product, its carrier, as well as the gypsum product increased aggregate stability compared to the control soil. Most pronounced effects were seen in relation to the rainfall-runoff experiment where the microbial-based product had a clear effect on soil erodibility. In relation to measurement of aggregate stability as well as clay dispersion, the picture was less clear. Especially for the sandy Tanzania soil with a low content of organic matter, a clear effect was seen on the aggregate stability. However, the effect was minor for both the microbial-based product and the carrier treatments.