Abstract: In August and September 2010, a quantitative survey was conducted on the plant species in the farmland drainage ditches in the Ninth drainage area of Hetao Irrigation Region. One hundred and ten herbage plots with an area of 0.5 m × 0.5 m and thirteen shrub plots with an area of 5 m × 5 m were set at the bed and slope of the trenches in the upper-, mid-, and lower reaches of the main, feeder, and sub-feeder drainage ditches. A total of 39 species belonging to 38 genera and 17 families were found. Gramineae (n=10), Compositae (n=7), and Chenopodiaceae (n=4) were the largest families in the flora. The widespread plants species were Phragmites communis Trin., Leymus chinensis (Trin.) Tzvel., and Saussurea salsa (Pall.) Spreng. The Shannon index, richness Index, Pielou index, and Simpson index in the main drainage ditches were 0.57, 1.93, 0.37 and 0.81, those in feeder drainage ditches were 0.77, 3.46, 0.65 and 0.50, and those in sub-feeder drainage ditches were 0.90, 3.88, 0.64 and 0.53, respectively. The species diversity at slope was higher than that at bed, but the difference was not statistically significant between different size drainage ditches. Water retention time and dredging could be the main factors affecting the plant species diversity in the farmland drainage ditches in study area.

Key words: landfill, nitrous oxide, greenhouse gas, emission mechanisms, flux measurement