Soil microbial biomass and mineralization of carbon and nitrogen in ecological, integrated and conventional forage and arable cropping systems |
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Authors: | T A Breland R Eltun |
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Institution: | Agricultural University of Norway, Department of Chemistry and Biotechnology, P.O. Box 5040, N-1432 ?s, Norway e-mail: tor.arvid.breland@ipf.nlh.no, Tel.: +47-64947733 Fax: +47-64947802, NO The Norwegian Crop Research Institute, Apelsvoll Research Centre, N-2848 Kapp, Norway, NO
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Abstract: | In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage
(FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring
grain plots and incubated for 449 days at controlled temperature (15 °C) and moisture content (50% water-holding capacity).
There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of
microbial biomass C and N, microbial quotient (Cmic/Corg), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were
similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient
(qCO2) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not
differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a
decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE
of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil
aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized
that the lower qCO2 values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms
within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations,
but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced
tillage intensity in the ECO-ARABLE rotation.
Received: 28 October 1998 |
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Keywords: | Cropping systems Microbial biomass Carbon mineralization Nitrogen mineralization Conceptual humus fractions |
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