This study aimed to evaluate and quantify the methodology of stable isotopes, 15N values for the organic fertilizer (chicken manure) and inorganic (urea). In addition to evaluating the incorporation rate, chemical half-life and analysis thereof, for possible traceability through the pasture fertilized with different sources of N. The technique of employment with use of tracer stable isotope 15N possible to estimate the changes in the N soil, even in the face of the various changes that take place concurrently. The methodology determines the path of both N isotopes (15N and 14N), providing information about the system and estimating N transformation rates The experimental work was conducted at the Faculty of Veterinary Medicine and Animal Science, UNESP Botucatu. An area of 576m2 was used for the parcels, which were divided between the 3 treatments with 4 repetitions each: T1 - control treatment without fertilization; T2 - fertilization with urea and T3 - organic fertilizer with poultry litter. The grass was cut every 15 days, three months after fertilization, for a total of four periods of grazing exclusion. Experimental samples were analyzed for the isotopic nitrogen and crude protein, neutral detergent fiber, acid detergent fiber, cellulose, hemicellulose and lignin composition. Degradation of poultry litter, the sand bag method was analyzed by linear regression. (delta-N-15) forage, fodder percentage of nitrogen, percentage of total nitrogen sheet, (delta-N-15) on the sheet, and (delta-N-15) at the helm were different between treatments. To this end collection, difference was observed for% Total Nitrogen, % Total N in sheet, % Total N in the trunk and% Total N at the helm. The crude protein analysis revealed significant differences between treatments, while the crude protein and lignin differ according to time after fertilization. The technique of N stable isotope effectively distinguish the composition of organic and inorganic fertilizers in deferred grazing pastures of Urochloa brizantha cv. Marandu. Forage quality was not influenced by the source of N.