Agriculture Reference
In-Depth Information
far been left behind by the conservation agriculture movement (Giller et al. 2009).
Long-term research on different types of conservation practices, and associated
ecosystem services, is also urgently required. There is a tremendous variety of till-
age equipment and integrated practices that can be pursued in combination with
manure, cover crops, and rotational crop sequences; all are expected to influence
the ecosystem services that are generated.
Organic Agriculture
The principles of organic (biologically based) management are closely aligned with
a “semi-closed” system that mainly relies on biological processes to regenerate soil
resources and support the growth of healthy plants and animals (Pearson 2007). The
duration and diversity of active plant growth and the synchronization of N avail-
ability with plant N demand are important features of biologically based manage-
ment. Following these principles in the MCSE Biologically Based system resulted
in enhanced biological N fixation (almost 2-fold higher than in the Conventional
system, Fig. 15.1) and soil C gains (25% more than in the Conventional system)
that were slow to accrue but occurred in spite of more frequent soil disturbance.
Evidence also exists that available soil P has been maintained despite low P inputs
(Fig. 15.1). Energy inputs were low in the Biologically Based system compared
to Conventional (4.8 GJ ha
−1
yr
−1
vs. 7.1 GJ ha
−1
yr
−1
in Conventional, Table 15.2).
Biologically based crops used no fossil fuel-derived agrochemicals other than fuel
for field operations, so total farming energy inputs were equivalent to those of the
No-till system.
The yield reductions of cereals observed in the Biologically Based system could
be considered a worthwhile trade-off for enhanced ecosystem services, although
yield trade-off estimates for nitrate leaching and soil C sequestration in the MCSE
indicate that gains in those ecosystem services are negated by the loss in yield
(Table 15.3). There are also additional costs incurred for this system and for the
Reduced Input system, including labor, tillage, and cover crop establishment, offset
somewhat by the lower costs associated with reduced pesticide and fertilizer use.
The energy balance conducted for the MCSE systems reflects the lower yield of
cereals and net change in inputs associated with the Biologically Based system
(Table 15.2).
A significant challenge associated with biologically based management is
the labor and land investment in growing cover crops that fix N and build soil C
(Drinkwater and Snapp 2007). Not only does this incur seed and management costs
for a plant that provides little or no cash value, it also involves opportunity costs.
That is, planting diverse crops can infringe on the window of time and resources
required to grow higher value crops. For example, cover crops enhance ecosystem
services by providing soil cover and active rooting throughout the year. However,
planting a summer cash crop is necessarily delayed by the need to first kill and
plow under the cover crop. It is also important to allow cover crop residues time
to decompose, and the result is an even later planting window. This reduces the
length of the growing season, and may require planting shorter season varieties that
