Agriculture Reference
In-Depth Information
In the MCSE, relative to the Conventional system, the Reduced Input system stands
out for its ability to reduce nitrate loss and accumulate soil C while maintaining
high grain yields. While the Biologically Based system has provided greater nitrate
and C conservation benefits, yields have been substantially lower, resulting in a
significant yield vs. ecosystem service trade-off. Likewise in the LFL, ecosystem
service benefits in the Organic system come at the cost of a significant yield pen-
alty (Table 15.3). The extent to which these trade-offs might be acceptable will
depend on many factors, including the goals and economic position of land manag-
ers. Public interests as embedded in policy will also need to assess trade-offs among
services, weighing the relative and absolute value of different services to society.
Trade-offs also exist between crop yield and greenhouse gas mitigation services,
which can be evaluated as reductions in the global warming impact (GWI). The
MCSE No-till system combines high yields with a high soil C sequestration poten-
tial, and even in the face of higher chemical use, the No-till system had a low net
GWI (-14 g CO
2
e m
−2
yr
−1
) as compared to the Conventional system (101 g CO
2
e
m
−2
yr
−1
; Gelfand and Robertson 2015, Chapter 12 in this volume). In both systems,
N fertilizer use contributed similarly to GWI, as did the enhanced liming require-
ment associated with fertilizer use. Other long-term experiments have shown that
N fertilization is associated with decreased exchangeable calcium, magnesium, and
potassium levels, and lower cation exchange capacity, leading to increased require-
ments for liming (Liu et al. 1997). The direct relationship of N fertilization with
liming requirements, as well as the role of liming in the overall GWI of agricultural
systems, was evaluated at KBS and for agricultural row-crop systems in general by
Hamilton et al. (2007).
The Biologically Based system also provides greenhouse gas mitigation ser-
vices. This system uses no N fertilizer and sequesters considerable soil C over the
long term (note that no C gains were observed initially; Robertson et al. 2000).
However, the moderate grain yields associated with the Biologically Based system
reduce its net energy gain (Table 15.2) and raise its greenhouse gas intensity (g
CO
2
e per unit yield). Low productivity would also be expected to jeopardize profit-
ability, which is a precondition for economic sustainability. The current profitabil-
ity of the Biologically Based system depends to a considerable extent on a market
premium, such as those typically paid for organic products (Chavas et al. 2009,
Jolejole 2009).
Overall, the costs and benefits associated with biodiversity and other alternative
practices are complex. The interaction of management practice and cropping sys-
tem diversity is a primary focus of the LFL, discussed in the next section.
Agronomic Insights from the KBS LFL
Productivity
On a global basis, there is a growing requirement for grain for food and livestock
feed. The quantity of grain produced is the most important service provided by field
crops, and it is a key determinant of profitability on many farms. The type of grain
