Soil management and production of alfisols in the semi-arid tropics .2. Deriving USDA curve numbers from rainfall simulator data

A comparison of USDA-SCS runoff curve numbers from model calibration using experimental runoff data and rainfall simulation is presented. A rainfall simulator was used to derive curve numbers for a range of antecedent soil water contents and surface cover conditions for an Alfisol soil in the semi-arid tropics of India. These relationships between cover and curve number are compared with relationships that were obtained using model calibration in Part I of this paper. The results showed that rainfall simulation on dry soils was most useful for deriving curve numbers. Derived curve numbers under dry antecedent conditions (CN1) can be easily adjusted to curve numbers for average antecedent conditions (CN2) which is an input parameter for many agricultural simulation models. Further analysis of the effects of cover on curve number showed that a linear function explained up to 86% of the variability between curve number and surface cover. Curve numbers derived from rainfall simulators were similar to those obtained from model calibration. This has improved confidence in using rainfall simulation to measure a runoff curve number.