Stable isotope ¹⁵N and ¹³C are widely used in the research of plant physiology and biochemistry, nutrition of soil and plant, plant protection, the improvement of rice, flower, agricultural products and other crops, nitrogen cycle of grassplot. The products applied in the agricultural mostly are of low enrichment.. ¹⁵N labeled urea, ¹⁵N labeled ammonium sulfate, ¹⁵N labeled ammonium nitrate, ¹⁵N labeled ammonium chloride and other inorganic salts of low enrichment are the commonly used as fertilizer tracers.