Agriculture Reference
In-Depth Information
Low
soil quality
High
soil quality
Productivity
Healthy food supply
Environmental protection
Land stewardship
Soil organic matter
Erosion/sedimentation
Soil microbial activity
Biological diversity
Water quality
Air quality
Human condition
Soil quality relates directly to the
functions performed by soil
High-quality soil is able to produce abundant plant materials,
which feed, clothe, and provide shelter to humans. Plant residues
not consumed must be returned to the soil to feed soil organisms
and provide the organic nutrients for creating a biologically active
food web. High-quality soil protects the environment from degradation,
by stopping soil erosion and nutrient runoff (i.e., water quality
protection) and by storing carbon in soil and reducing greenhouse gas
emissions.
Low-quality soil lacks sufficient organic matter to sustain
productivity in the long term, leads to excessive soil erosion and
poor water quality, has low soil biological activity and diversity,
and could lead to an unhealthy food supply and human condition.
Low
?
Low
Low
Low
High
Low
Low
Poor
Poor
?
High
Yes
High
High
High
Low
High
High
Clean
Clean
Healthy
FIGURE 4.5
Conceptual depiction of how differences in soil quality of a particular land-
scape affect various ecosystem forms and functions.
How land is managed has a large impact on the trajectory of soil quality with time
(Figure 4.6). Changes in soil properties with time are a key component of dynamic
soil quality assessment. Sustainable cropping systems that improve soil quality indi-
cators with time (e.g., increase carbon stocks and flows) will lead to high soil quality,
often brought about through diverse crop rotations, minimal use of tillage for weed
control and seedbed preparation, and addition of organic amendments such as ani-
mal manures, crop residues, and compost. Management systems that cause a decline
in soil quality indicators with time (e.g., reduced carbon stock and flows) will lead to
low soil quality. This is often induced by overgrazing or cropping systems with low
residue retention, intensive tillage, and near monoculture cultivation.
The terrestrial carbon cycle is dominated by two important fluxes, photosynthesis
(net ecosystem uptake of CO
2
from the atmosphere) and respiration (release of car-
bon back to the atmosphere via plant, animal, and soil microbial respiration) (Figure
4.7). Biochemical transformations occur at numerous stages in the carbon cycle, e.g.,
simple sugars in plants are converted into complex carbon-containing compounds,
