Influence Of Different Levels Of Nitrogen On Nitrogen Fixation In Sugarcane (Saccharum Officinarum L.)

Two sugarcane (saccharum offtcinarum L.) varieties RB72/454 and RB86/7515, introduced from Brazil were inoculated with the N₂-fixing bacterium Herbaspirillum rubrisubalbicans. The plants were cultured with Hoagland nutrition solution that contained different levels of nitrogen in pot trial with sand in greenhouse. Nitrogenase activity,nitrogen metabolism and other physiological or biochemical indexes were measured at different stages, and the experimental results were as follows:1. The nitrogenase activity was quite different in different parts such as leaves, prime leaf viens, leaf sheaths, stalk internodes, roots and rhizosphere, which showed considerably higher in the internodes, roots and rhizosphere.2. The nitrogenase activity in the stalk internodes was inhibited by high nitrogen concentrations from early to mid growth stages. When sucrose accumulated in the stalk internodes fast, however, the nitrogenase activity in the internodes could not be inhibited by higher nitrogen application under rich carbon source condition.3. The diazotrophic bacteria were more active under the condition of low nitrogen condition in the variety RB72/454, which showed higher N and chlorophy content in the leaves as compared with the control.4. Under lower nitrogen conditions, active nitrogenase promoted the absorption of Fe, resulting in higher Fe content in the leaves.