Abstract: The results of field experiments at four stations in different parts of China indicate that the crop yield increment caused by recycled nutrients within an agricultural ecosystem was significantly influenced by the thermal condition of climate, the application of fertilizers and the duration of the experiments lasted.In the case of no fertilizer, the average crop yield increment caused by recycled nutrients with a 0.8 recycling rate ranged from 253kg·hm^-2 (average of ten years) at Hailun station (in temperate zone) to 1122kg·hm^-2 (six years) at Shenyang station and 1332kg·hm^-2 (eight years) at Kezuo Xiahetao station (in warmer-temperate zone), and to 2884kg·hm^-2 (seven years) at Taoyuan station (in subtropical zone), while on the base of applying Nand Pfertilizers, the corresponding increments at the four stations were 225, 694, 786 and 1321kg·hm^-2 respectively.There was a marked accumulative residual effect of recycled nutrients in farmyard manure on crop yields, based on N, Pand Kfertilizers, the average increase rate of crop yields caused by recycled manure was about 5% in the first three years, but raised up to about 14% in the last three years within the experimental period.

Key words: Agro-ecosystem, Use of recycled nutrients, Geographic differentiation of yield increase efficiency, biological nitrogen fixation, soil nitrogen pool, plant nitrogen pool, Cenchrus spinifex