The leaching losses of indigenous and applied nitrate-nitrogen were measured for the non-weighing lysimeter in soils under the condition of winter wheat cropping. The transfer function model (TFM) developed by Jury et al. and White was used to simulate nitrate-nitrogen transport through unsaturated heterogeneous soils. The probability density functions (pdfs) of the travel times of the nitrate-nitrogen under the experiment condition were determined from the normalized rates of loss of nitrate-nitrogen mass...