Different methods fòr separating diffuse and direct components of solar radiation and their application in crops growth models

Four methods to estimate daily and hourly values of direct and diffuse radiation from measurements of global radiation are compared both in terms of accuracy of incoming solar component estimates and of their suitability for incorporation into two wheat growth- simulation models (NWHEAT and SUCROS 90). Comparison showed that 1) the accuracy of direct and diffuse component estimates tends to decrease with increasing temporal resolution and varies under different climatic conditions and 2) the final grain yield calculated by the models is slightly but significantly influenced by the method used to calculate the components of incoming radiation.