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TECHNICAL REPORTS

Surface Water Quality

Nitrogen Loss through Lateral Seepage in Near-Trench Paddy Fields

Dep. of Environmental Engineering, College of Natural Resources and Environmental Science, Zhejiang Univ., Hangzhou, 310029,China

^* Corresponding author (liang410{at}zju.edu.cn).

Received for publication February 9, 2007. A near-trench paddy field experiment with five urea application rates (0–360 kg N ha^–1 in 90-kg increments) was conducted on a paddy soil in the Taihu Lake Region of China to elucidate N losses through lateral seepage during three rice (Oryza sativa L.) growing seasons. The total N (N_t), NH₄⁺–N, and NO₃^–-N concentrations in the lateral seepage water increased with increasing N rates. The seasonal N_t fluxes by lateral seepage varied from 6.8 to 25.6 kg N ha^–1 for urea application rates of 90 to 360 kg N ha^–1. Lateral seepage accounted for 4.7 to 6.6% of the N_t applied, implying that lateral seepage was an important pathway of N loss from near-trench paddy fields. The cumulative N loss via lateral seepage was significantly related to N fertilization rate (P = 0.05). Floodwater level was also identified as a main factor affecting N losses via lateral seepage from paddy fields, as indicated by a positive linear relationship (R² = 0.43) between floodwater level and daily lateral flow during the flooded period (P = 0.05). Under the conditions of these experiments, a shallow floodwater depth of 50 mm, urea application rates of 90 kg N ha^–1 or less, and no rainfall within 1 wk after N application reduced N losses by lateral seepage from paddy fields.

Abbreviations: N_t, total N