During the entire experiment period, AP concentrations in CK,
SR and GM treatments remained at an extremely low level
(approximately 1.80 mg?kg21) and were almost the same as the
initial values. On the contrary, AP in both OM and NPK
treatments displayed similar changes over time. Specifically, the
value rose sharply in the first few years of fertilization (63.59 and
45.54 mg?kg21 respectively in 2003) then progressively reduced till
2007 (25.37 and 16.68 mg?kg21 respectively) and later increased
slightly (Fig.8B).