Some traits like ear leaf area, plant height, grain yield, karnel weight, grain n2 content, nitrate content, chlorophyll content... Any more traits i can take into study???
It depends upon the hypothesis and objective you have. How did you hypothesized that Maize can fix atmospheric nitrogen? It must have some special features to fix nitrogen. Like leguminous plants have symbiotic property with Rhizobium which assists in Nitrogen fixation. So if your plants are growing in nitrogen free medium, second thing you need to do is, to search for the special features in the plants which assist nitrogen fixation.