Agriculture Reference
In-Depth Information
A
Integrated Management
1
50
Bacteria
Fungi Root
0.8
40
0.6
30
0.4
20
0.2
10
0
0
18-Apr
20-Jun
30-Jul
19-Aug
11-Nov
Sample Date
B
Conventional Management
1
50
Bacteria
Fungi Root
0.8
40
0.6
30
0.4
20
0.2
10
0
0
19-Aug
18-Apr
20-Jun
30-Jul
11-Nov
Sample Date
Figure 4.9
Proportion of total food web biomass for the functional groups within the bacterial,
fungal, and root energy channels and potential N mineralization (kg NO
3
ha
−1
) from soils collected
over a growing season in winter wheat under integrated (A) and conventional management (B) at
the Loevinkhoeve Farm, Marknesse, the Netherlands.
The increase in microbial activity is not limited to increases in microbial biomass but to a
shift in the relative abundances and activities of organisms within the bacterial and fun-
gal energy channels as well. The observed increases in microbial activity, respiration, and
mineralization can be attributed to an increase in the biomass and activity of bacteria and
their consumers (i.e., the bacterial energy channel) and the loss of biomass and activity of
fungi and their consumers (i.e., the fungal energy channel).
Management practices affect not only the relative abundances and activities of organ-
isms within the different energy channels but also their timing. In natural ecosystems,
the timing of microbial activity and mineralization is in synchrony with plant growth
and uptake. In temperate regions, this often involves a pulse of activity in both the bac-
terial and fungal energy channels, but with some degree of spatial separation (read
compartmentalization) within the soil profile (Holland and Coleman, 1987) and tempo-
ral separation within the growing season (Moore and de Ruiter, 1991). During the fall
and winter, processes proceed but at reduced rates. The seasonal cycle in some respects
resets in the spring and repeats the cycle. What has emerged from comparative studies
of conventional and minimum tillage practices is a pattern of biotic activity and result-
ing processes late in the growing season in intensively managed systems that are out of
synchrony with plant growth and management. Minimum tillage practices tend to retain
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