Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9620183 | Forest Ecology and Management | 2005 | 13 Pages |
Abstract
An experiment was conducted to evaluate the influence of repeated application of sewage sludge, on N dynamics in soils under Monterey pine (Pinus radiata D. Don.) stands. Sludge with a total N concentration of 4.2% was applied at four different loading rates (0, 2.4, 17, and 60 Mg haâ1 yearâ1, DW equivalent), in two consecutive autumns. Soils were sampled once a year to a depth of 53 cm, and leachates were collected at 25 and 50 cm depth, after heavy rain. The soils under study have low pH (4.1-4.4), low CEC, and low base saturation (<15% below the first 4 cm depth), typical of soils located in a high leaching environment. Addition of municipal sewage sludge at a rate of 2.4 Mg haâ1 in two consecutive years did not result in significant NO3â-N and NH4+-N leaching, with concentrations in leachates at 50 cm below 10 and 0.3 mg Lâ1, respectively, although nitrification was enhanced after the second application. The higher doses of sludge resulted in contamination of groundwater by NO3â-N and NH4+-N, even after only one application, with peaks of 104.2 and 48.7 mg Lâ1, respectively, for the 60 Mg haâ1 treatment. Soil acidification at depth was observed with all treatments (pH ranging from 3.6 to 4.0). Plant analysis indicated that mean foliar N concentration was significantly greater (P < 0.01) in the control (22.0 g kgâ1) than in the sludge amended pine trees (all <17.5 g kgâ1), whereas the inverse pattern was observed for mean foliar P (3.0 mg kgâ1 versus >4.0 mg kgâ1). Pine growth, as indicated by the trunk diameter, was significantly greater (P < 0.05) in the sludge-amended stands than in the control stands, whereas there were no significant differences (P < 0.05) between the different sludge treatments. The concentration of NO3â-N in leachates from the control plots was high (mean at 50 cm depth: 19.6 mg Lâ1 NO3â-N) due to subsurface lateral flow, therefore differences in plant growth were attributed to P deficiency in the non-amended plots. The results obtained indicated that in this weakly acid-buffered forest soil, sewage sludge application at a low rate (2.4 Mg haâ1) in two consecutive years is a feasible method of fertilisation - if lime is applied to counterbalance the acidifying effect of N oxidation - with minimal risk of groundwater contamination by NO3â, although the risk of heavy metal contamination has yet to be clarified.
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Authors
G. Egiarte, M. Camps Arbestain, A. Alonso, E. RuÃz-Romera, M. Pinto,