Soil carbon, nitrogen and phosphorus contents in maize plots after 14 years of pig slurry applications

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 (C,), total nitrogen (N1), 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 x 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, Pi and PM3 contents increased with increasing rates of LPM application. The zone of maximum accumulation of Ci, 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.