Agriculture Reference
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than twice as long (26 years) as any other fi eld in the study. High EOC
and EON in this fi eld may be indicative of a diversity of organic moieties
built up over time with organic management (Aranda et al., 2011) and sup-
portive of a more unique microbial community composition (Giacometti
et al., 2013).
Despite differences in management, the relative abundance of FAMEs
indicative of saprophytic fungi and the fungi:bacteria ratio was much more
consistent across fi elds than bacterial FAMEs. Disturbance intensity and
frequency appear to be lower in landscapes where studies have shown
positive relationships between the fungi: bacteria ratio and soil C and soil
C:N (Fierer et al., 2009 and de Vries et al., 2012). Saprophytic fungi are
well-known to be particularly sensitive to certain management practices,
especially tillage and fertilization (Minoshima et al., 2007). Tillage in-
tensity was similar across the 13 fi elds, since these organically-managed
farms rely on cultivation as a means of weed control and for incorporat-
ing organic amendments. While organic management may increase fungi
relative to conventional management (Bossio et al., 1998), routine soil
disturbance may represent a strong fi lter for fungi, such that only a resis-
tant subset persist in arable soils in this area (Calderón et al., 2000 and
Young-Mathews et al., 2010). In contrast to saprophytic fungi, the rela-
tive abundance of a FAME biomarker for AMF, 16.1ω5c, was distinctly
different across fi elds. A signifi cant negative relationship (p = 0.017, R 2 =
0.45) was found between the relative abundance of this marker and Olsen
P when fi eld 12, which has high Olsen P, is excluded from the analysis.
This is in line with other studies in agricultural landscapes ( Williams and
Hedlund, 2013) and refl ects the sensitivity of AMF to P availability.
13.4.3 ON-FARM APPROACH TO MICROBIAL COMMUNITY
FUNCTIONING
The on-farm approach used in this study provided a range of SOM char-
acteristics (e.g. a three-fold range of total soil C and N) and organic nutri-
ent management practices to investigate how these factors influence soil
microbes and ecosystem functions while controlling for other factors to
the extent possible in a real landscape. Narrowing a landscape's extent to
 
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