Excessive applications of liquid pig manure (LPM) could result
in
nutrient accumulation in the soil,
thereby increasing the potential for plant nutrient losses through
movement in groundwater. The
objective of this work was to measure the concentrations of total
carbon (Ct), total nitrogen (Nt), total
phosphorus (Pt) and Mehlich-3 extractable-P (PM3)
with depth in a Le Bras silty loam soil growing
maize (Zea maize L.) under reduced tillage conditions.
The soil was fertilized annually with various
rates of LPM (0, 30, 60, 90 and 120 m3/ha) in four
completely randomized blocks since 1979. In
autumn 1992, twenty soil plots were sampled in increments of 20 cm to
a depth of 1·0 m and analysed
for total C, total N, total P and Mehlich-3 extractable-P. LPM application
rate (R), soil depth (D)
and the interaction R × D had highly significant
(P<0·001) linear effects on Ct, Nt,
Pt and PM3
concentrations throughout the 100-cm depth profiles. At all depths,
Ct, Nt, Pt and PM3 contents
increased with increasing rates of LPM application. The zone of maximum
accumulation of Ct, Nt,
Pt and PM3 concentrations occurred at the first
0–40 cm depth. A significant relationship was found
between soil organic matter and Nt, Pt and PM3.
Differences in N and P concentrations between
manure rates are due to manure and maize. The increase in PM3
was generally greater for soil samples
with high Pt content. Results from this study indicate
that long-term application of a high rate of
LPM leads to greater total C, N and P concentrations in the soil profile.