Agriculture Reference
In-Depth Information
The same approach can be used to examine the combined effect of year and cli-
mate on crop yield at the local scale. For example, Fig. 4.11 shows yield increases
in corn and soybean in Kalamazoo County, Michigan—the location of the KBS
LTER—during the 1971-2001 period, with slopes of 0.094 (
r
2
= 0.47) and 0.042
(
r
2
= 0.51), respectively. This yield trend also reflects technological advances, as it
did at the regional level (Fig. 4.4). However, incorporating both year and climate
does not improve the prediction of yield for Kalamazoo County (Fig. 4.12) as much
as it did for the NCR (Fig. 4.10). At the county level, the CSI explains only 26% of
the yield variance for corn (vs. 48% for the region) and 11% of the yield variance
for soybeans (vs. 41% for the region).
The CSIs for Kalamazoo County during this time frame were not as extreme as they
were in the NCR; in fact, locally only 1 year out of 30 had a CSI value greater than 25
(Fig. 4.12), whereas in the NCR, the CSI was greater than 25 in 5 out of the 30 years
examined (Fig. 4.10). This is likely because Kalamazoo County is in the northern part
of the NCR where temperatures are cooler and rainfall is greater than in the western
(A) Corn
8
6
4
Yield = -179.8 + 0.094 Year
r
2
= 0.47
2
0
(B) Soybean
3
2
1
Yield = -80.36 + 0.042 Year
r
2
= 0.51
0
1970
1975
1980
1985
1990
1995
2000
Figure 4.11
. Trends in grain yields of (A) corn and (B) soybean in Kalamazoo County,
Michigan (1971-2001). See Figs. 4.3 and 4.6 for data sources.
