Ishaemum rugosum is one of the most important weeds in irrigated rice in the state of Maranhão, Brazil. An experiment was conducted to evaluate the nitrogen content in the leaf, stem and root of I. rugosum under three levels of shading (10, 60 and 70%) at 91 and 112 days after emergence and in the panicle at 133 DAE. Nitrogen levels were greater in the leaf, stem, roots and panicles at 70% of shading compared to either 60 or 10% shading. However, vegetative parts of the rice plants showed greater nitrogen content at 91 DAE. It was concluded that shading increased nitrogen content of plants os I. rugosum.
weed; irrigated rice
