Agriculture Reference
In-Depth Information
linkages (Robertson et al. 2007). For example, while it has been long known how
bacteria in streams and wetlands can transform excess nitrate (NO
3
−
) that leaves
farm fields into harmless dinitrogen (N
2
) gas (Lowrance et al. 1984, Robertson
and Groffman 2015), only recently have headwater streams and small wetlands in
agricultural landscapes been shown to disproportionately improve water quality
(Mulholland et al. 2009, Hamilton 2015, Chapter 11 in this volume). Likewise, rel-
atively small areas of uncropped habitat can disproportionately support biodiversity
services via the provision of refugia for pollinators and insect predators important
to pest suppression (Gardiner et al. 2009).
How can row crops be managed to balance or reduce the negative impacts of
agricultural production? The answer lies in knowing how to manage cropland for an
array of ecosystem services, and that area of research remains largely unexplored.
Of particular importance is an understanding of how different cropping systems
vary in their impacts—environmental, economic, as well as social—and how they
interact with unmanaged ecosystems. By fully comprehending the causes and con-
sequences of these impacts and interactions we can identify (1) which components
and interactions are important for delivering the services we value and (2) how this
knowledge can be used to promote beneficial services and minimize the negative
impacts of agriculture at different geographic scales.
Many processes and attributes that provide ecosystem services in agricultural
landscapes take decades to occur or become visible. Thus, long-term observations
are crucial for detecting change (Magnuson 1990, Scheffer et al. 2009). Some
changes are gradual, such as trends in soil organic matter (Paul et al. 2015, Chapter
5 in this volume) and shifts in soil microbial communities (Schmidt and Waldron
2015, Chapter 6 in this volume). Others may be more rapid with clear immediate
effects but still have long-term, perhaps subtle consequences. The appearance and
persistence of exotic pests and their predators (Landis and Gage 2015, Chapter 8
in this volume) and the adoption of new genomic technologies (Snapp et al. 2015,
Chapter 15 in this volume) might fit this description. And still other changes can be
highly episodic, such as the outbreak of a pest that affects a dominant competitor or
a 20-year drought that affects later plant populations via seed bank changes (Gross
et al. 2015, Chapter 7 in this volume). Short-term observations might entirely
miss episodic events or lack the temporal context to fully understand events with
long-term consequences. Century-long experiments at Rothamsted in England
(Jenkinson 1991) and at a few U.S. sites (Rasmussen et al. 1998) have illustrated
the importance of long-term observations and experiments for understanding the
impact of agriculture on many slowly changing ecosystem attributes (Robertson et
al. 2008a).
Understanding the complexity of intensive field-crop ecosystems thus requires
a long-term systems perspective: understanding (1) potential ecosystem services
and how multiple services can be delivered in synergistic ways; (2) how local,
interdependent communities in agricultural landscapes interact across landscapes
and regions; and (3) how the component parts of agricultural ecosystems behave
and interact over appropriate, often long time scales. Sustainable agriculture
depends on this knowledge (Robertson and Harwood 2013). And the prospect of
human-induced climate change coupled with increasing demands for agriculture to
