Aggregate Stability and Phosphorous Loss from Soils Treated with Biosolids.

Solid organic material recovered from sewage treatment processes, also known as compost, sewage sludge, or biosolids, can help maintain soil nutrient levels (e.g., nutrient P availability) and may also change soil physical properties.  However, nutrient P loss by wind erosion or runoff from biosolid-amended arable soils as well as leaching often leads to deterioration of water quality.  The objectives of this study were to investigate the effects of biosolids addition (control, composted manure, activated sludge), incubation duration (6 rain storms with a 4 day incubation break between each storm), and spiking of the soils with orthophosphate, phytic acid or humic acid on (i) aggregate stability; (ii) infiltration, runoff and soil loss; and (iii) P transport by infiltrated and runoff water in a loamy sand, a loam and a clay soil.  Aggregate stability was found to depend on an interaction between the effects of soil and biosolid types and the role of the breakdown mechanisms (slaking, swelling and dispersion).  Soil aggregate stability subjected to raindrop impact was in the following order: control>manure>sludge. Total runoff form the control and the manure treated soils was comparable but was lower than from the sludge-amended soil.  However, soil loss was significantly lower in the sludge-treated soils compared with the control and the manure treated clays and loams.  Sediment transported by the infiltrated water was higher in the sludge treatments, whereas in other treatments their amount was similar. The total removal of orthophosphate and total P from the loam and loamy sand was: control<manure<sludge.  Under varying environmental conditions a given biosolid can release multiple organic compounds that may have different effects on aggregation, infiltration, and erosion.  This work might be helpful in assessing potential risks of surface water eutrophication and evaluating vertical P transport in semi-arid soils amended with two common biosolids.