Since dissolved organic matter is mobile in soils, it is
possible that compost additions increased DOC levels
below the 0 to 15-cm sampling depth, which may have
influenced NO3 and P dynamics in surface soils. Compost
application to sandy soils caused an initial large vertical
flux of dissolved organic matter, followed by a lower and
more stable flux (Kaschl et al., 2002). These results may
explain the initial increases in DOC and available P
observed in our study soon after compost application, followed
by a slower rate of increase in DOC and P from 3 to
29 months. Compost application possibly contributed to
greater amounts of DOC and available P than were
observed in surface soil, but these materials may have leached
below the 0 to 15-cm sampling depth. In fact, organic
amendments applied to St. Augustinegrass at high P rates
caused P movement below 30 cm in sandy soils (Johnson
et al., 2004).