Abstract: Taking a long-term fertilized rice-rape rotation system in Taihu Lake as test objective, its annual C balance and economic benefit were estimated, based on th e measurement of past years grain yield, litter C content, and field CO2 emission as well as the investigation of material and management inputs. The ca lculated annual C sink under different fertilizations ranged from 09 t C·hm -2·a-1 to 75 t C·hm-2·a-1, and the net C sink effect under combined inorganic/organic fertilization was three folds as that under che mical fertilization. The C cost of material input ranged from 037 t C·hm- 2·a-1 to 113 t C·hm-2·a-1, and that of management input ranged from 169 t C·hm-2·a-1 to 183 t C·hm-2·a-1 . The annual economic benefit ranged from 58×103 CNY·hm-2·a -1 to 165×103 CNY·hm-2·a-1, and was 21 times higher under combined fertilization than under chemical fertilization. Comparing with that u nder chemical fertilization, the marginal cost for per ton C sink under combined inorganic/organic fertilization was estimated as 2171 CNY· t-1 C, very close to the C price of 20 Euro·t-1 C in the EU. In sum, under combined inorgani c/organic fertilization, this rice paddy ecosystem could not only have higher pr oductivity, but also present greater net C sink effect and higher economic benef it, compared with under chemical fertilizer fertilization.

Key words: root cell wall of tea plant, lead, chemical modification, adsorption.