Agriculture Reference
In-Depth Information
microbially-derived ecosystem functions and thus may be a model system
for ecological intensification of agriculture (Jackson et al., 2012). By fo-
cusing on building and utilizing soil organic matter (SOM) as opposed to
using synthetic fertilizers, organic production systems differ greatly from
conventional systems; organic management in many research station trials
has been shown to improve soil fertility (Burger and Jackson, 2003 and
Gattinger et al., 2012), reduce nutrient losses (Drinkwater and Wagoner,
1998, Kramer et al., 2006 and Syswerda et al., 2012), and reduce global
warming potential (Burger et al., 2005 and Cavigelli et al., 2013) while
supporting similar crop yields in certain contexts (Seufert et al., 2012).
Yet, such research station-based experiments may belie the challenge
of evaluating multiple ecosystem services on working organic farms
across actual landscapes that vary in topography, soil type, commodities,
and motivations of farmers for making the organic transition (Darnhofer et
al., 2005 and Williams and Hedlund, 2013). Organic farms also use many
different nutrient management strategies (Guthman, 2000 and Darnhofer
et al., 2010) even when growing the same crop in the same region (e.g.
Drinkwater et al., 1995 and García-Ruiz et al., 2008). While this heteroge-
neity could help explain some of the ambiguous results of landscape-scale
comparisons of organic and conventional farms relative to site-specifi c
experiments (e.g. Williams and Hedlund, 2013), we lack basic understand-
ing of how heterogeneity affects soil microbial activity and community
composition and the implications for soil ecosystem functions and agro-
ecosystem management.
The quantity and quality of SOM and carbon (C) and nitrogen (N)
inputs are the overriding controls on soil microbial biomass and activity
(Fierer et al., 2009 and Kallenbach and Grandy, 2011). Thus, distinct or-
ganic amendments (e.g. manure, leguminous cover crops, and composted
materials) can stimulate microbial biomass differently through increases
in labile organic matter (Marriott and Wander, 2006, Smukler et al., 2008
and Kallenbach and Grandy, 2011) and/or total soil C on time frames from
months to decades (Drinkwater and Wagoner, 1998 and Kong et al., 2005).
However, little is known about how the quantity and composition of SOM
and nutrient inputs (e.g. C:N ratio) affect microbial communities and their
enzyme activities, and in turn, transformations of C, N, phosphorus (P),
and sulfur (S) on organic farms. The total enzymatic activity of soil, de-
