The release and transport of soil chemicals in surface runoff is not only an agricultural issue

but also a problem of the quality of surface and ground waters.Soil bulk density is one of the important factors affecting soil chemicals transportation with runoff.The characteristics of soil nitrogen

phosphorus and potassium transport with surface runoff on two types of soil from Loess Plateau were studied by simulating rainfall indoor.Results indicated that

when soil bulk density increased

the runoff initiation time shortened

runoff coefficient increased

soil erosion became heavy

and soil phosphorus and potassium loss increased.The sequence of extent of soil bulk density influencing on chemical concentration in runoff was NO-3-N>PO3-4-P>K .There was one peak during the chemical loss from runoff.The characteristics of peak

including time arrived peak to spend and quantity of peak value

was results from the synthetical interaction of soil bulk density

physical and chemical characteristics of chemicals and other hydrologic parameters.By simulating results

it was further confirmed that power function was the optimal model to fit the process of runoff chemical concentration under unsaturated condition and without rill erosion on the loess section.The study offered a reference for understanding the mechanism of soil nutrient in runoff transport of the loess slope.