Emergy Evaluation of three Rice Wetland Farming Systems in the Taihu Lake Catchment of China

Emergy analysis was performed to evaluate the sustainability of three rice farming systems (rice mono-cropping, rice-fish and rice-duck farming systems) in the Jiangsu province. The results showed that the three systems exhibit unique characteristics on each component. The emergy of rice seeding and the labour input were the most important costs, at 57.18 and 18.20 sej/ha/season, respectively, for the rice mono-cropping system. In the rice-fish and rice-duck systems, the feed input played a more important role, corresponding to values of 63.70 and 79.20 sej/ha/season, respectively. The machinery input was 45.21 sej/ha/season for the rice-fish system due to the construction of fish ponds and ditches. The rice-duck system exhibited lower environmental loading and a higher sustainability index than the rice mono-cropping and rice-fish systems, respectively. The ratios of the economic input to output were 0.41, 0.61 and 0.41 for the rice mono-cropping, rice-fish and rice-duck systems, respectively. The net profit of the rice-duck system was $3264.2 per hectare, which was nearly 40% higher than those of the other systems. Based on the results showing the highest economic efficiency and value on the sustainability index, the rice-duck system may be the optimal rice agriculture system from both ecological and economic perspectives.