the three wheat seasons. This conclusion is supported by the following
evidence: the 40 cm depth exhibited higher TN concentration
values initially but lower values later than deeper soil depths at
the later stages of wheat growth, and the high peaks of TN concentration
were usually found in percolation water from 100 cm
soil depth (Fig. 4b). The applications of fertilizer N did not always
induce immediate peaks in N concentration in percolation water,
implying that the majority of N that was not taken up by wheat
plants might have accumulated in the cultivated soil layer after N
fertilization. When a heavy rain event occurred, N could be flushed
out and move downward through percolation and runoff.