Substantial development is needed in the production of pollution鄄free vegetables to ensure the quality, safety, and competitiveness of vegetables in China. In contrast to customary vegetable production, pollution鄄free production uses organic fertilizers and biological pesticides instead of chemical fertilizers and chemical pesticides. This mode of production improves the safety of the vegetables and reduces environmental pollution, and the government is encouraging its use throughout China. Nevertheless, there is still considerable scope for research into efficient and sustainable vegetable production. Emergy evaluation is an effective tool in analyzing the efficiency and sustainability of an ecological system, which addresses the weakness of traditional energy analysis and expresses different forms of energy using a common physical basis, namely, solar emergy. It also has the advantage of taking into consideration aspects such as natural resources, labor,

Effect of different planting methods on root鄄 shoot characteristics and grain yield of summer maize under high densities. Acta Ecologica Sinica,2012,32(23) :7391鄄 7401.

Raising duck in paddy field is a traditional agricultural model in China. This model can increase the efficiency of using paddy field while rice plant is growing. Field experiments on C cycling from rice鄄duck mutual ecosystem were conducted from May to October in 2010 in the double cropping rice region in Hunan, and a conventional rice field was used as control. The Input鄄Output Analysis method was applied in this study to analyze C cycling in both rice鄄duck and conventional rice fields. Throughout the plant growing season, neither chemical pesticides nor herbicides were applied in rice鄄duck mutual ecosystems, and the surface water was maintained about 10 cm in depth during the period of raising ducks. Ducks of 22鄄day鄄old were introduced into the paddy field based on the holding capacity of 450 ducks per ha 24 days after seedling of early rice transplantation. Ducks of 30鄄day鄄old were introduced into the paddy field based on the holding capacity of 450 ducks per ha 10 days after seedling of late rice transplantation. These ducks were retrieved after the complete heading stage of rice in the experiments. During the early rice growth season, the recycled C from weed and insects in rice鄄duck mutual ecosystems were 60. 53 kg / hm 2 and 2. 75 kg / hm 2 , respectively. The C inputs from urea, duckling, plant seedling and feed were 22. 5 kg / hm 2 ; 15. 79 kg / hm 2 ; 20. 42 kg / hm 2 and 630. 56 kg / hm 2 , respectively. While the C outputs in the rice鄄duck mutual ecosystems consisted of 42. 21% rice seed, 38. 42% rice straws, 18. 50%