Modeling runoff and soil water balance under mechanized conservation tillage in dry land of north China

PERFECT (Productivity Erosion and Runoff Functions to Evaluate Conservation Techniques), which has been widely used in Australia, is designed to predict runoff, erosion and crop yield under various management pratices including residue, tillage, sequences of plantings, harvesting and stubble managements in dryland cropping areas. The objectives of this study were to modify and calibrate PERFECT to simulate the impacts of tillage, residue and traffic on runoff and soil water balance under conservation tillage of small- to medium-sized machinery, and to assist identifying appropriate conservation practices for sustained crop production in dry land areas of Northern China. The procedure of runoff prediction using USDA Curve Numbers was modified by incorporating the effects of field slope and rainfall intensity. Runoff was calculated daily as a function of rainfall, soil water, residue cover, slope, surface roughness resulted from tillage, and rainfall energy. A simplified Priestley-Taylor equation was employed in the model to calculate potential evapotranspiration, and the effect of residue cover on evapotranspiration was also considered in the model. Input data for the simulation model included daily weather, runoff, soil hydraulic properties, plant available water capacity, cropping systems, and traffic and tillage management. Data were collected from field experiments on Loess Plateau of Northern China. Preliminary results of model calibration and validation showed that the R 2 between predicted and observed runoff was 0.86~0.90 and R 2 between predicted and observed available soil moisture was 0.82~0.94.