Abstract: ¹⁵N was used to study the cycling of fertilizer N in the ecosystem of film mulching. Results showed that 18.56% of the N in the corn stalks, returned to the field under the conditions of film mulching, was absorbed by the first crop corn, while 59.09% was left in the soil. The second crop wheat and the third crop summer millet absorbed 4.04% and 2.89% of the stalk N respectively. Corn utilized 38.44% of the ammonium sulfate, of which 15.80% was distributed among the stems, leaves and roots, participating in the recycling of nutrients. But, in this way, the loss of N was rather great, amounting to about 50% of the N input.3.4% of the stalk N residue left in the soil was in the undecomposed stalk while 3.5% moved to the lower stratum(30-50cm), and 45.8% was combined with soil minerals. There was very little fertilizer N residue left, most of which entered the organo-mineral complex, while a part of the soil N was activated.

Key words: Nitrogen, Mulching, Cycling, Residue, Organo-mineral complex