Designing Cropping Systems for Ecosystem Services - The Ecology of Agricultural Landscapes - page 389

solute loss in general, and is important in its own right as a contributor to indirect
N 2 O fluxes downstream (Beaulieu et al. 2011), to human health via groundwater
drinking water supplies (Powlson et al. 2008), and to coastal eutrophication (Diaz
and Rosenberg 2008).
That nitrate loss differs among MCSE cropping systems provides another
metric for gauging differences in their delivery of ecosystem services. To the
extent that N conservation can be considered an ecosystem service, then, the
system with the lowest nitrate loss (either absolute or relative to yield) can be
considered a greater service provider. While the system with the greatest loss
could conversely be viewed as the greater disservice provider, comparisons are
more straightforward if put in terms of positive services (Swinton et al. 2015a,
Chapter 3 in this volume).
By this metric, then, for the annual cropping systems of the MCSE, in absolute
terms the Biologically Based system provided the most nitrate conservation, with
average leaching losses of 19 kg NO 3 − -N ha −1 yr −1 over an 11-year (1995-2006)
period (Syswerda et al. 2012). This compares to the Conventional system's aver-
age loss of 62 kg NO 3 − -N ha −1 yr −1 . The No-till and Reduced Input systems were
intermediate to these at 42 and 24 kg NO 3 − -N ha −1 yr −1 , respectively. In relative
yield-scaled terms, the differences were smaller but the rankings identical: 18, 11,
7.3, and 7.2 kg NO 3 − -N Mg −1 yield for Conventional, No-till, Reduced Input, and
Biologically Based systems, respectively.
Pest Suppression
An important regulating ecosystem service that can be affected by agricultural
management practices is suppression of pests. Weeds are a particularly important
group of pests because they reduce crop quality by competing for soil nutrients,
water, and light, and by interfering with harvest. Agricultural practices such as till-
age, crop rotation, fertilizer and herbicide application, and cover crop use can affect
weed populations directly by causing seedling mortality, by inhibiting or promot-
ing seed germination, and by changing weed nutrient status (Liebman et al. 2001).
Management practices can also affect weeds indirectly by altering weed-crop
competitive relationships (Liebman and Davis 2000, Ryan et al. 2010) or through
effects on seed predator populations (Menalled et al. 2007). Management addition-
ally influences soil processes, such as feedbacks with soil biota that reduce weed
survival and fitness (Li and Kremer 2000, Davis and Renner 2007).
Weed population data have been collected regularly in the MCSE systems (Gross
et al. 2015, Chapter 7 in this volume). The most recent syntheses of these data
indicate that the four annual row-crop systems differ in terms of capacity for weed
suppression (Davis et al. 2005; Gross et al. 2015, Chapter 7 in this volume). In
general, the Biologically Based system is the least weed suppressive (i.e., has more
weeds), with weed biomass varying across years from 48 to 148 g m −2 compared to
the other three systems, where biomass has ranged from less than 3 to over 50 g m −2
(Davis et al. 2005). The lack of herbicide use and reduced crop productivity in the
Biologically Based system have likely contributed to this system's weed pressure.