RADIATION USE-EFFICIENCY OF FIELD BEANS AS AFFECTED BY SOIL-PHOSPHORUS MANAGEMENT

A simple approach to modeling dry matter production is based on the assumption that radiation-use efficiency (RUE), which is the amount of dry weight produced per unit of intercepted photosynthetically active radiation (IPAR), is relatively constant for crops adequately supplied with water and nutrients. Recent evidences, however, indicate that RUE is not constant but is strongly affected by environment. Soil stresses also appear to affect RUE but few responses have been documented. Growth analysis data from a field experiment were used to compute RUE of field beans grown at differential phosphorus (P) regimes. The main objective of this study was to assess the effects of soil P management on RUE. Applied P rates significantly increased RUE with values ranging from 0.86 g M/J at 0 kg P/ha to 1.09 g M/J at 200 kg P/ha. The relationship between total dry matter and cumulative IPAR was linear at low P regimes but resembled a curvilinear relationship at high P regimes. The RUE of beans under high soil P regimes was not constant but decreased over time.