An evaluation of net carbon sink effect and cost/benefits of a rice-rape rotation ecosystem under long-term fertilization from Tai Lake region of China
太湖地区长期施肥条件下水稻-油菜轮作生态系统净碳汇效应及收益评估

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 the measurement of past years grain yield, litter C content, and field CO2 emission as well as the investigation of material and management inputs. The calculated 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 chemical 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 5.8×103 CNY·hm-2·a-1 to 16.5×103 CNY·hm-2·a-1, and was 2.1 times higher under combined fertilization than under chemical fertilization. Comparing with that under 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 inorganic/organic fertilization, this rice paddy ecosystem could not only have higher productivity, but also present greater net C sink effect and higher economic benefit, compared with under chemical fertilizer fertilization.