Nitrogen balance and economic benefit in Zizania latifolia-duck mutual ecosystem.

Nitrogen(N)input, N output, N surplus(N surplus=N input-N output), and economic benefit under different ecological systems were analyzed, including Zizania latifolia monoculture ecosystem and three Zizania latifolia-duck mutual ecosystems such as with 20 ducks per 667 m2(D20), 25 ducks per 667 m2(D25)and 30 ducks per 667 m2(D30). The results showed that the average yield of Zizania latifolia for three mutual ecosystems was 1 332.41 kg·667 m-2, 26.31% higher than that for monoculture ecosystem. For Zizania latifolia monoculture ecosystem, total N input was 22.27 kg N·667 m-2, and chemical fertilizer N was accounted for 89.10%, the N output by the harvest was 5.00 kg N·667 m-2, 22.45% of total N input, N surplus was 17.27 kg N·667 m-2, 77.55% of total N input. For three mutual ecosystems, the average total N input was 23.72 kg N·667 m-2, and chemical fertilizer N was accounted for 65.13%, the average N output by the harvest of Zizania latifolia and duck mutual ecosystem was 7.65 kg N·667 m-2, 32.24% of total N input, the average N surplus was 16.07 kg N·667 m-2, 67.76% of total N input. Because of the costs of duck feed, fence and duck shed, the average input cost for three Zizania latifolia-duck mutual ecosystems was 3 114 yuan·667 m-2, 84.59% higher than that for Zizania latifolia monoculture ecosystem. The average economic income for three Zizania latifolia-duck mutual ecosystems was 6 568 yuan·667 m-2, 55.64% higher than that for Zizania latifolia monoculture ecosystem. For D25 treatment, the economic benefit(economic benefit =economic income-input cost)was the highest as 3 589 yuan·667 m-2, 41.69%higher than that fo r Zizania latifolia monoculture ecosystem. In view of N balance and economic benefit, Zizania latifolia-duck mutual ecosystem with 25 ducks per 667 m2 had lower N surplus with less environmental risk, and higher economic benefit.