The total amount of leaching water in rice season is defined as
the rate of surface water vertical percolation (mm day−1)
×
flooded
periods (day)
×
10. Flooding condition in most period of rice season
provided an approximately constant rate of water moving through
soil profile. Therefore, the rate of surface water vertical percolation
in rice season during flooded periods was measured using
the percolation meter as illustrated in Fig. 3b. Compared with the
water balance method, this method significantly simplified the calculation
of the leaching water amount and reduced the error. The
amount of water that percolated vertically through the cylinder
equaled the amount that passed through the transparent tube on
the float. In the current study field, the rate of vertical percolation
was averaged at 2 mm day−1 from 15 replicate measurements
distributed well in the plot.