RUNOFF WATER QUALITY FROM CONSTRUCTED ROADSIDE SOILS RECEIVING LARGE VOLUME-BASED COMPOST APPLICATIONS

Rapid soil stabilization after construction in highway right-of-ways is important to limit erosion. The Texas Department of Transportation (TxDOT) developed methods for stabilizing constructed soils utilizing compost. Three of the methods are: compost manufactured topsoil (CMT), general-use compost (GUC), and erosion control compost (ECC). Volume- or depth-based compost amendments may promote stabilization by revegetation and thereby reduce runoff and sediment losses. The quantity of compost associated with the application rates may be apotential nonpoint source of dissolved and particulate nutrients. Runoff losses of dissolved and particulate-bound nutrients and particulate matter were observed during eight natural runoff events from soils on an 8.5% slope amended according to TxDOT specifications for CMT, GUC, and ECC. Composted dairy manure (CDM) was used to meet the specifications for the soil amendments. The addition of CDM increased soil test phosphorus (STP) and NO(3)-N concentrations above the critical nutrient level for Princess bermudagrass (Cynodon dactylon (L.) Pers). Although the STP and NO(3)-N concentrations in soil were greatest in the ECC, the ECC was most effective at reducing both runoff and particulate mass loss. The reduced runoff volume from ECC kept total mass loses similar among ECC and CMT and GUC. The benefit of using the ECC was a reduction in runoff depth and particulate loss without greater overall nutrient losses, even though the ECC utilized 262% and 584% more CDM than the CMT and GUC amendments, respectively.