Artificial draining is one important factor dominating N runoff in
rice season. Currently, direct seeding instead of transplanting has
become a popular cultivation pattern due to its convenience and
cost economics in practice (Pandey et al., 2002). A drainage event is
usually conducted after steeping the field (pre-flooding) in order to
provide drained soil for rice seed broadcasting and the emergence
of rice seedlings (which usually takes 10–15 days). Drainage events
also occur during several midseason aerations (MSA) to inhibit ineffective
tillering, and again at the mature stage before rice harvest.
N runoff loss is inevitable due to these frequent artificial drainages.