Effect of application method on copper transport by runoff from sloping lateritic red soils amended with sewage sludge

The effects of different application methods of sewage sludge on Cu transport by runoff from sloping plots in lateritic red soils were investigated under simulated rainfall conditions. When the sludge is broadcasted and mixed with surface soils, the concentrations and loss of MTCu (total Cu in mixed sample), STCu (total Cu in settled sample), TPCu (total particulate Cu), TSCu (total suspended Cu) and TDCu (total dissolved Cu) in runoff are highest on the 1st and 18th day after application. The peaks of concentration and loss of MTCu, STCu are 1 674.9 μg·L^-1, 105.4 μg·L^-1 and 21.59 mg·m^-2, 1.32 mg·m^-2, which are respectively 4.2~13.7 and 5.4~24.9 times of corresponding peak values under hole-application and broadcast-application with hay mulch. After that, both the concentration and loss of Cu gradually decrease with the treatment time. Broadcast-application with hay mulch reduces Cu concentration in runoff by 72.8%~91.7% and Cu loss via runoff by 91.4%~97.1%, compared with the broadcast-application alone. Cu concentration in runoff and Cu loss via runoff reduce by 78.2%~89.9% and 68.6%~82.9% respectively under hole-application, compared with those under broadcast-application. MTCu loss coefficients via runoff are 0.83%, 0.03% and 0.26% for broadcast-application, broadcast-application with hay mulch and hole-application. Hole-application, but especially broadcast-application with hay mulch, is effective for controlling Cu loss by runoff. Particle-bound Cu is the major form of Cu loss via runoff.