The SOC in different treatments had a similar trend over time
(Fig.4A). From 1998 to 2004, the SOC showed a clear increase
with time due to fertilization, rising from initial 9.65–9.78 g?kg21
to 11.51–20.00 g?kg21 in 2004, respectively. Then SOC content
dropped sharply but quickly reached at stable level. It was also
obtained that the SOC content in OM was obviously higher than