Agriculture Reference
In-Depth Information
•
Enabling animal habitat and serving as a reservoir for biodiversity (micro-
scopic and visible)
•
Buffering against toxic accumulation (e.g., salts) and transport of natural
and synthetic compounds
•
Filtering elements to protect animals, plants, and the environment from
undesirable exposure
Land managers and scientists do not have unlimited time and resources to study
all of the potential functions served by soil in a region, nor can they predict future
needs or demands on soil resources. Soil quality assessments often use a small group
of indicators (i.e., a minimum data set) to economically and efficiently characterize
selected key soil functions, distinguishing between static and dynamic soil proper-
ties. Topography, hydrology, and climate also affect productivity and environmental
quality of a site, somewhat independent of management. Static soil properties pro-
vide the contextual background for how soil management practices might eventually
alter dynamic soil properties and reflect the inherent characteristics of a particular
site, e.g., soil texture, mineralogy, and classification, all of which are influenced by
geologic history and climatic conditions. Dynamic soil properties are those prop-
erties that can change value over relatively short time periods (e.g., months, years,
and decades) and are at the leading edge of soil quality assessment because they are
sensitive to management. Dynamic soil properties can indicate whether a produc-
tion system uses agronomically and ecologically sustainable practices. Static as well
as dynamic soil properties have been characterized in North America with regional
sampling approaches by the USDA-NRCS through the periodic National Resources
Inventory (Brejda et al. 2000). Similar efforts have been conducted by Agriculture and
Agri-Food Canada (MacDonald et al. 1995). Sanchez et al. (2009) described global
soil mapping efforts and resources; however, site-specific assessments of static and
dynamic soil properties for monitoring soil quality trends remain limited at all scales.
4.2.1 S
oIl
o
rGanIc
m
atter
One of the most consistent and broadly applied indicators of soil quality is soil
organic matter content. Soil organic matter is often defined by carbon and nitro-
gen contents owing to their overwhelming importance, i.e., carbon is ~58% of soil
organic matter, while nitrogen is typically 4%-7% of soil organic matter and is often
the most limiting element for plant production. Changing soil organic matter often
leads to large changes in soil properties and processes at all scales (Figure 4.5).
Perennial forages offer clear benefits to soil quality by producing high carbon inputs
and providing vegetative cover to protect the surface from raindrop impact and ero-
sion. From the Sanborn Field in Missouri, topsoil thickness at the end of 100 years
of management averaged 20 cm under continuous corn (
Zea mays
), 31 cm under
a 6-year rotation of corn-oat (
Avena sativa
)-wheat (
Triticum aestivum
)-red clover
(
Trifolium pratense
)-timothy (
Phleum pratense
)-timothy, and 44 cm under continu-
ous timothy (Gantzer et al. 1990). Soil erosion rates predicted from the universal
soil loss equation in this study averaged 19, 2.5, and 0.3 Mg ha
−1
year
−1
for the three
management systems, respectively.
