Soil Quality: What is it? And is this a useful concept for precision agriculture
and the management of natural resources? October, 2000
by D. Keith Morris, Information Systems Manager,
SSMC
People have different ideas on what makes a quality soil.
For example, for producers in production agriculture, it may mean high yielding
land, sustaining or enhancing productivity, maximizing profits, or maintaining
the soil resource for future generations; for consumers, it may mean plentiful,
healthful, safe, and inexpensive food for the present and for future
generations; for naturalists, it may mean soil in harmony with the landscape
and its surroundings; for the environmentalist, it may mean soil functioning at
its potential in an ecosystem with respect to maintenance or enhancement of
biodiversity, water quality, nutrient cycling, and biomass production.
Understanding soil quality means assessing and
managing soil so that it functions optimally now and is not degraded for future
use. Much like air and water, the
quality of soil has a profound effect on the health and productivity of a given
ecosystem and the environments related to it.
However, unlike air and water for which we have quality standards, the
definition of soil quality is complicated because it is not directly consumed
by humans and animals (Doran et al., 1996).
Historically, farmers have viewed soil
quality/health as a function of yield potential and nutrient levels. In recent years they have also come to the
realization that the biological health of the soil is profoundly important
(Roming et al. 1996). Soil quality cannot be measured directly, so we evaluate
indicators. Indicators are measurable properties of soil or plants that provide
clues about how well the soil can function. Indicators can be a variety of
physical, chemical, and biological characteristics. However, descriptive
indicators and quantitative means to monitor soil quality are at best difficult
to define. Arshad and Conan (1992) gave
possible descriptive indicators to characterize soil quality which include
evidence of erosion, soil structure, friability, crusting of the soil surface
and ponding of water. All of these are
physical attributes of the soil and to a certain extent can be controlled by
Best Management Practices and are somewhat qualitative in nature. Quantitative measures to monitor soils such
as soil pH and extractable N-P-K are more developed and are still being
explored as to how these measures affect yield, nutrient levels and the
biological health of the soil. Many
decades of research have consistently shown that the best means of improving
and/or restoring soil quality/health is by proper and regular additions of
organic matter primarily through the use of cover crops, crop residues,
manures, and reduced tillage practices.
Precision agriculture provides a tremendous
opportunity to aid in the monitoring and maintenance of soil quality. Current soil sampling routines either on a
grid system or zone management have the potential to help farmers monitor the
condition of their soil over time.
Yield monitor data, along with as-applied fertilizer,
herbicide/pesticide maps and site-specific manure application all document what
was done, where it was done and how it was done. This documentation is essential in identifying possible soil
quality indicators that may be used to identify reasons for poor yielding areas
that cannot be explained by routine whole-field soil testing. Also,
environmental monitoring/documentation of inputs will help characterize how these
inputs move through the ecosystem.
As we enter the 21st century, producers must be
increasingly aware of the fact that the environment is a closed system. The agricultural inputs that are supplied do
not disappear; they are simply redistributed over time. The goal should be to control their movement
and protect fragile resources such as soil quality. Environmental consciousness must not be considered a nuisance,
but a requirement for survival.
Arshad, M.A. and G.M. Coen. 1992. Characterization of
Soil Quality: Physical and
Chemical
Criteria. American J of Alternative Agriculture. 7: 25-30.
Doran, J.W. and T.B. Parkin. 1996. Methods for Assessing Soil Quality. SSSA
Spec.
Publ. 49. Soil Science Society of America,
Madison, WI.
Roming, D.E., M.J. Garlynd, and R.F. Harris. 1996. Farmer-Based Assessment of Soil
Quality: A Soil Health
Scorecard.
SSSA Spec. Publ. 49. Soil Science Society of
America,
Madison, WI.