Agriculture Reference
In-Depth Information
grasslands (Symstad et al. 2003, Collins et al. 1998) remain rare in KBS MCSE
Early Successional communities (Table 7.4), likely because of their absence from
the surrounding landscapes.
Controls on Productivity
Voluminous evidence exists that the productivity of terrestrial ecosystems is lim-
ited by nutrients (Chapin et al. 1986, Elser et al. 2007) and N has repeatedly been
shown to be a critical limiting nutrient in both natural and agricultural temper-
ate ecosystems (Drinkwater and Snapp 2007, LeBauer and Treseder 2008). Across
North American grasslands and other “low-stature” herbaceous plant communities,
the response to N-fertilization can depend on species composition, soil nutrient
status (Clark et al. 2007), and interannual variation in precipitation (Cleland et al.
2013). While the magnitude of a productivity response to N-fertilization can vary
across communities, generally there is an increase in aboveground biomass pro-
duction and a decrease in species richness (Gough et al. 2000, Suding et al. 2005).
Thus, N fertilizing agricultural systems to enhance productivity may come at the
expense of diversity, which may reduce or limit the ecosystem services they pro-
vide (Robertson et al. 2015, Chapter 2 in this volume). Few studies have examined
how enhancing plant species diversity can increase crop productivity or yield. In
fact, increasing the diversity of weed species is generally assumed to have a nega-
tive effect on crop yield, the primary ecosystem service expected from row-crop
agriculture.
Results from the MCSE cropping systems and Early Successional communities
have been included in several meta-analyses and cross-site syntheses of fertilization
experiments, allowing our results to be interpreted in a broader regional context
(Gough et al. 2000, Davis 2005, Suding et al. 2005, Smith 2006, Clark et al. 2007,
Smith and Gross 2007, Gough et al. 2012). We summarize studies from both the
cropping and Early Successional systems here to address our overall goal of apply-
ing lessons learned and insights gained from research in noncrop plant communi-
ties to the management of cropping systems, and vice versa.
Productivity in Successional Grasslands
The Disturbance by N-Fertilization Experiment, established within the MCSE Early
Successional plots, provides clear evidence that productivity in these systems is
limited by N (Fig. 7.5). Although the magnitude of this effect varied across years—
likely driven by variation in seasonal precipitation (Robinson 2011, see Cleland et
al. 2013)—on average, the addition of fertilizer increased aboveground production
in both the untilled and annually tilled plots by approximately 50% (Dickson and
Gross 2013). There was a significant correlation between aboveground production
in the fertilized and unfertilized plots across years in the untilled treatment (Fig.
7.5A;
r
= 0.60), but not in the annually tilled treatment. Annual precipitation is a
significant predictor of productivity in both fertilized and unfertilized plots in the
untilled treatment (
r
= 0.49 and 0.37,
p
< 0.025 and 0.05, respectively), but not in
