Percolation water was collected with a vacuum hand pump usually
at 10-day intervals during rice season, but more frequently immediately
after fertilizer application. Likewise, percolation water was
collected after every rain event during wheat season. Water preexisting
in the porous pipe was drained and discarded before
sampling to avoid contamination. Runoff water in both seasons
was sampled at drainage outlet point when every drainage event
occurred. Samples of irrigation water in rice season were taken for
analysis at irrigation inlet point (Fig. 2) when every irrigation event
occurred. Percolation, runoff and irrigation water samples were
stored in 250 ml plastic bottles, and immediately frozen without filtering
at
−20 ◦C in a freezer until analysis. Concentrations of NH4
+,
NO3
−, and total N (TN) in these water samples were analyzed with
a continuous-flow N analyzer (Skalar, Netherlands, with analytic
error
±
3.9% and low detection limit of 0.2 mg N L−1).
Percolation water was collected with a vacuum hand pump usuallyat 10-day intervals during rice season, but more frequently immediatelyafter fertilizer application. Likewise, percolation water wascollected after every rain event during wheat season. Water preexistingin the porous pipe was drained and discarded beforesampling to avoid contamination. Runoff water in both seasonswas sampled at drainage outlet point when every drainage eventoccurred. Samples of irrigation water in rice season were taken foranalysis at irrigation inlet point (Fig. 2) when every irrigation eventoccurred. Percolation, runoff and irrigation water samples werestored in 250 ml plastic bottles, and immediately frozen without filteringat−20 ◦C in a freezer until analysis. Concentrations of NH4+,NO3−, and total N (TN) in these water samples were analyzed witha continuous-flow N analyzer (Skalar, Netherlands, with analyticerror±3.9% and low detection limit of 0.2 mg N L−1).
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