Agriculture Reference
In-Depth Information
a smaller geographic area allowed for sampling generally similar soils, in
terms of texture, mineralogy, and parent material, while still encompass-
ing a range of farming strategies. Focusing on the same crop controlled for
the effect of plant species and plant functional traits, which also strongly
influence the microbial community (Gardner et al., 2011). Since timing
(relative to seasonal and agronomic events) can exert a strong influence
on enzyme activities and microbial community composition, we carefully
sampled during a defined crop phenological period when nutrient demand
was maximal (i.e. anthesis to early green fruit stage), which provided in-
sight into soil functions at a crucial time for crop productivity. Further-
more, the fields in this study were planted within a two-week period, and
this minimized the differential effects of temperature and rainfall on soil
biology and plant growth across fields. Since farmers in this area use ir-
rigation and summers are reliably hot and dry, inter-annual variability may
be reduced compared to locations with less predictable summer weather.
Differing nutrient management practices and SOM characteristics
across these fi elds reinforces the need for robust indicators of microbial-
ly-derived ecosystem functions to support management decisions, since
one-size-fi ts-all recommendations are not viable in such heterogeneous
systems. While MBC would have differentiated fi elds with apparently
compromised soil quality (i.e. fi elds 1 and 2) from others, it would not
have differentiated more subtle variation related to potential activities of
C- and N-cycling enzymes, which may have important implications for
ecosystem functioning, such as suffi cient N availability with low potential
for N loss. Differences in enzyme activities in concert with specifi c C and
N pools may eventually be useful to farmers for improving site-specifi c
management to balance these types of tradeoffs. Such research comple-
ments nearby research station-based experiments (e.g. Bossio et al., 1998
and Kong et al., 2011), which were by design and necessity limited to a
relatively narrow set of practices at a single fi eld. In turn, such experiments
disentangle the relative effects of individual management practices and
examine long-term trends, which can be challenging in a landscape ap-
proach. A dynamic interplay between site-specifi c experimental research
and landscape-scale surveys of working farms may be the most promising
route to improving understanding and management of microbial processes
for ecological intensifi cation of agriculture.
