Abstract: A typical small area naturally enclosed by drainage and irrigation canals was selected to monitor and analyze the content and spatial variability of nitrogen and phosphorus in 0~10 cm sediment. The results showed that in the 36 sediment samples, the total nitrogen content was 0.7~2.9 g/kg, the average value was 1.79 g/kg. The total soluble nitrogen content was 17~166 mg/kg, the proportion of inorganic nitrogen in total soluble nitrogen was 88.1%~94.5%, the main part of inorganic nitrogen was ammonium nitrogen, the proportion of which was 84.7%~90.4%. The total phosphorus content of the ditch sediment was 0.4~1.3 g/kg, which averaged 0.60 g/kg, the Olsen-P was 10.2~131.7 mg/kg, accounting for 2.6%~10.1% of the total phosphorus, and the water-soluble phosphorus content was 0.5%~3.7% of Olsen-P. The total nitrogen, total soluble nitrogen and ammonium nitrogen, as well as total phosphorus, Olsen-P and water-soluble phosphorus in the ditch sediment showed a very significant positive correlation at the level of α=0.01. The average value of various form nitrogen in the ditch sediment was the highest in the laternal canal near the fish pond, while the highest phosphorus content was observed in the branch canal near the residential area.

Key words: ditch sediment, nitrogen, phosphorus, small area, Jianghan plain