Soil Management in Site-Specific Agriculture June 2001
Purdue University Site-Specific Management Center
1150 Lilly Hall, Room 3458
West Lafayette, IN 47907-1150
Phone: (765) 496-6472
Soil is the foundation for everything we do.
Farmers, consultants, and researchers alike have realized for years that the
spatial variability of soil is difficult to assess. With the advent of site-specific management practices, within-field
variability of yield, soil, topography, soil electro-conductivity, etc. have
come to the forefront and are now being addressed by research in the form of
field scale on-farm trials by both producers and universities.
The
characterization of soil properties is a daunting task at best. In the past, farmers have relied upon
published soil surveys which were produced in the 1940's and 1950's for the
most part. When these soil surveys were
created their primary purpose was for "land-planning" such as drainage
and erosion control. These soil surveys
also contain predictions of soil behavior for selected land uses. They also
highlight limitations and hazards inherent in the soil, improvements needed to
overcome limitations, and the impact of selected land uses on the
environment. Even though yield
potential was a part of these predictions, they were/are very subjective in
nature.
Farmers,
consultants, and soil scientists have long professed that there is as much
variability within soil types as there is between soil types,
especially when one uses the current soil survey as a decision making
tool. The current soil survey was never
intended to be used to make management decisions on the scale that is now
possible using the new technologies of GPS, GIS, and remote sensing. Published soil surveys are typically on a
scale of 1:15,840 or 1:24,000, and with the new technologies, we are able to
map areas in the range of 1:500 or smaller.
The
current "buzzword" in site-specific management is the need for a
"1st Order Soil Survey". This
soil mapping procedure approaches a scale of 1:500 -- a scale that is also
possible with current yield monitor data.
However, this scale of mapping is extremely labor intensive and requires
an expertise that is usually the result of years of experience. Two of the first things an experienced soil
scientist looks for when he/she enters a field that is to be mapped are the
topography/landform and soil color/tone characteristics of the soil. These two characteristics are indicators of
several different soil attributes such as OM content, water holding capacity,
water availability, to a certain extent CEC, depth to till, etc., all of which
are important in determining soil variability and ultimately yield variability. Thus, remote sensing has the potential to
aid in the characterization of these soil properties. Soil color and topography
data in the past have been used to generate soil and topographic maps; however,
the resolution of the images was not fine enough to be used at a field
scale. With the emergence of high
resolution (~1m) image data both multi-spectral and in some cases
hyper-spectral, we are now able to "view" an area that is comparable
to the area we obtain using site-specific tools.
Crop
consultants, fertilize dealers and farmers themselves are in search of
"management zones" which will allow them to explore "spatial
variations" within a particular area of a field as a subset of the whole
field. Until now these "management
zones" have been dictated by computer programs which only allowed farmers
to manage areas in small blocks (i.e. grids).
These blocks have commonly been 1 acre to 2 1/2 acres in size and could
either be square or rectangular in shape.
However, as we all know Mother Nature does not display her wares in
squares or rectangles, and this method of soil sampling does not account for
"non-linear factors" located within a square or rectangular grid,
such as change in soil type, drainage problems, topographic changes, etc.
Currently,
soil physical and chemical properties are both difficult and expensive to
evaluate on a site-specific basis.
Precision agriculture is in its infancy, and how the spatial
characteristics of soil affect yield is even less understood. Correlations with yield are mediocre at best,
because of interactions with weather and other factors, such as both soil
physical and chemical properties, insect pressures, weed infestations,
etc.. Future research will need to
address the scale at which we need to manage these attributes, which properties
are yield limiting for specific sites, and how we will manage our agricultural
inputs in an "environmentally friendly" manner.
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.