Microbial nitrogen dynamics in south central Chilean agricultural and forest ecosystems located on an Andisol |
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Authors: | Dries Huygens Dries Roobroeck Lynn Cosyn Francisco Salazar Roberto Godoy Pascal Boeckx |
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Affiliation: | (1) Laboratory of Applied Physical Chemistry, ISOFYS, Faculty of Bioscience Engineering, Ghent University, Coupure 653, Ghent, Belgium;(2) Institute of Soil Science and Agricultural Engineering, Faculty of Agricultural Sciences, Universidad Austral de Chile, Casilla 567, Valdivia, Chile;(3) National Institute for Agricultural Research, INIA-Chile, P.O. Box 24-O, Osorno, Chile;(4) Institute of Botany, Faculty of Sciences, Universidad Austral de Chile, Valdivia, Chile |
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Abstract: | The natural soil N supply in volcanic soils (Andisols) can be a significant source of plant-available N for agro-ecosystems.
Nevertheless, intensive farming systems in south Chile apply high fertilization rates, which lead to high production costs
and involve a risk for adverse ecosystem effects. In order to achieve sustainable land management, a better understanding
of the processes that govern soil N availability and loss, and their external drivers, is required. In this study, we selected
a winter-cropland, a summer crop-winter fallow rotation, and a forest, used as a reference ecosystem. Gross N transformations
(15N isotope dilution) and microbial community structure (phospho-lipid fatty acid analysis) in the topsoil were determined.
Gross N mineralization was about ten times lower in the agro-ecosystems than in the forest, while gross nitrification was
low in all sites. Gross N immobilization equalized or exceeded the gross inorganic N production in all sites. Microbial biomass
was 3–5 times more abundant in the forest than in the agro-ecosystems. A positive relationship between the ratio fungi/bacteria
and total microbial biomass was observed in these Andisols. We suggest that the reduction in fungal biomass induced a lower
extracellular enzyme production and limited soil organic matter depolymerisation in the agro-ecosystems. We conclude that
soil N cycling was unable to provide a significant N input for the croplands, but also the risk for ecosystem N losses was
low, even under fallow soil conditions. Current fertilization practices appropriately anticipated the soil N cycling processes,
but further research should indicate the potential of alternative land management to reduce fertilizer cost. |
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