Abstract: ¹⁵N labelled technique was used for understanding the transferring and cycling of nitrogen in micro-agroecosystems with soil-ryegrass-rabbits-rice compartments and soil rice compartments. Preliminary results showed that the utilizational rate of (NH₄)₂SO₄ by ryegrass was 59.36% for the above ground portion and 9.79% for roots. As ¹⁵N labelled ryegrass was comsumed by rabbit, the ¹⁵N labelled recovery rates in feces and urine collected were 11.78% and 17.95% respectively. Rabbit excrement-nitrogen was integrated with inorganic fertilizer nitrogen in different proportions as 1:0, 0.5:0.5, 0.3:0.7 and 0:1 for rice culture. Results showed that the uptake of nitrogen by rice plant was 67—70% from the soil and 30—33% from fertilizers.The utilizational rates by rice plant were increased with the proportion of inorganic nitrogen. They were 36.94%, 40.52%, 40.73% and 43.91% for treatment 1—4. The yield of rice grain decreased with the proportion of inorganic nitrogen, however. The functional effects of organic fertilizer on the ecosystems were:(l) promoting the ear and root development of rice plant;(2) increasing the transferring ability of nitrogen from straw to rice grain, especially in 0.5:0.5; (3)maintaining inorganic fertilizer nitrogen in soil; (4)decreasing losses of nitrogen to air and waters. In treatment 0.3:0.7, the utilizational rate of organic fertilizer nitrogen was enhanced, and no considerable increment of utilizational rate of inorganic fertilizer nitrogen was found in the study. According to the complexity of food chain and the nitrogen recycling indexes in different microecosystems, it is considered that the maturity and stability of the ecosystem were higher in treatments 1:0, 0.5:0.5, and 0.3:0.7, but lower in the treatment 0:1 which consists of rice plantation and relaying on inorganic fertilizers only.

Key words: ¹⁵N labelled technique, Micro-agroecosystem, Organic and inorganic fertilizer N, Cycling of N, Recycling index