Agriculture Reference
In-Depth Information
ecosystems for this provisioning. But to what extent do high yields depend on
current common management practices? The results from other long-term experi-
ments (e.g., Drinkwater et al. 1998) suggest that more complex rotations using
fewer inputs can provide similar or greater yields than those of conventional rota-
tions. Our results suggest that simpler rotations of major grains can be managed to
provide other ecosystem services as well.
Corn and soybean yields under Conventional management at the KBS LTER site
are similar to the average yields for both the entire United States and Kalamazoo
County; wheat yields are higher (Robertson and Hamilton 2015, Chapter 1 in this
volume). In our Reduced Input system, corn and soybean yields slightly exceed
those of our conventionally managed system, and wheat yields lag only slightly
(Fig. 2.1). Indirect evidence points to nitrogen deficiency as the cause of the
depressed wheat yields: Whereas corn follows a nitrogen-fixing winter cover crop
and soybean fixes its own nitrogen, fall-planted wheat immediately follows the
soybean harvest, which leaves relatively little nitrogen-rich residue for the wheat
crop. This nitrogen deficit is especially apparent in the Biologically Based system,
which lacks fertilizer nitrogen inputs: Wheat yields are ~60% of the yields under
Figure 2.1
. Grain yields at KBS LTER under No-till, Reduced Input, and Biologically
Based management relative to Conventional management (dotted horizontal line) over the
23 year period of 1989-2012. Absolute yields for Conventional management are similar to
county and U.S. national average yields. Error bars represent the standard error. Redrawn
from Robertson et al. (2014).
