Relationship between Leaf Photosynthesis and Nitrogen Content of Field-Grown Rice in Tropics

A field-derived relationship between maximum single leaf net photosynthetic rate under saturating light (A max ) and leaf N content per unit leaf area (N a ) is not available for rice (Oryza sativa L.). The rice simulation model ORYZA1 estimates aboveground dry matter production based on the relationship between A max and N a determined previously under greenhouse-growth chamber conditions. The objectives of this study were to establish to relationship between A max and N a under field conditions and to determine whether the field-derived relationship could improve ORYZA1 estimation of aboveground dry matter production of tropical irrigated rice. Rice plants were grown in the field with different N rates in the 1993 dry season. The A max and N a were determined at 38 and 88 d after transplanting. Aboveground dry matter was determined at physiological maturity. Dry matter production data at physiological maturity from four other field experiments were used for model evaluation. There was a close correlation between A max and N a under field conditions (r 2 = 0.88). Compared with the relationship between A max and N a as determined under greenhouse-growth chamber conditions in previous studies, higher A max was observed at low N a in this field study. When the field-derived relationship between A max and N a was used, ORYZA1 estimation of dry matter production was improved for rice grown in tropical irrigated environments.