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Overview of Geological Conditions Effecting Soil Fertility
Central Ontario Wine Growing Region
By
John Slack
Agricultural Mineral Prospectors Inc.
P.O. Box 868
Erin Ontario, NOB ITO
519-833-9827
jslack@sentex.ca
Introduction
There are a diversity of soils found in Central Ontario ranging from
base saturated, mineralogical complex to low fertility acid soils. This
diversity is the result of Central Ontario’s unique geological setting.
The Kawartha Lakes area represents the divide between ancient
Precambrian rocks and overlying sea deposited sediments. The last
glacial period was responsible for mixing these two distinct
assemblages and depositing this heterogeneous mix into the landforms
that we see today. This recent geological event resulted in two quite
distinct landscapes and highlights the relationship between soil
development and geology. In the southern region the soils and
unconsolidated drift are rich in quartz, feldspar, mica, apatite,
calcite, magnesium carbonate, high-energy clay and a diversity of trace
minerals not commonly found in other Southern Ontario landscapes. This
diversity in mineralogy is the result of the regions proximity to the
Precambrian shield and particular the abundance of unique rock
formations rich in iron, phosphorous, zinc, cobalt, nickel, copper,
manganese, molybdenum, boron and rare earths mixed in a matrix of
calcareous (calcium rich) sand and silt. These unique rock formations,
referred to as ultramafic or alkalic intrusives supplied a diversity of
minerals and the calcareous sediments ensured their preservation in the
soil development process.
Samples taken from forest soils found in the Ottawa Valley and formed
under identical geological conditions and sourcing the same parent
bedrock formations attest to the mineral complexity and abundance of
plant nutrients and catalysts.
{ed note: file did not copy this chart properly}
Conversely this same geological selling created soils that are acidic
with very poor fertility and mineral complexity. The conditions where
this very contrasting soil exist are:
1. On the Precambrian Shield where no intermixing has occurred with
the limestone plains.
2. Southern regions where the receding glacier developed
eskers, sand outwash plains and deltas formed, almost entirely from
resistant quartz and feldspar sourced from the Canadian Shield.
Physiography of Central Ontario — Southern Region
The physiography, (the study of genesis and evolution of landforms),
for Southern Ontario can be divided into two parts based on bedrock.
The north characterized by Precambrian granites and the south by the
softer sedimentary limestones, shales and sandstones overlying the
Precambrian rocks. Within these two divisions there are differences due
to glaciation, erosion and water deposition, which requires further
division. These differences can be divided into physiographic regions.
The classification of soil parent material into regions is of major
importance in interpreting and recognizing unique soil fertility
conditions, soil structure, hydrology and soil formation associated
with a particular landform. Though major distribution patterns are not
simple and variations within a region occur the information collected
in one area of a particular region hold true for other areas within the
same region. This is to say that each physiographic region has a unique
geological footprint, which can explain how nutrients cycle, unique
mineral excesses or deficiencies.
The Wisconsin glacier began its retreated approximately 17,000 years
ago. The recession of the glacier was periodically interrupted by
periods of re-advancement or standstills. During these periods the ice
lobes frequently built end moraines along the ice margins. Moraine is a
term to describe the deposition of till in front of a stable glacier.
Stable meaning the glacier has reached the critical point where the
melting and replenishment are at equilibrium. This ensures a continuous
supply of rock debris deposited at the edge of the ice field. Moraines
are built of either glacial till or coarsely stratified sand and gravel
deposited by water from the melting ice. Associated behind and in front
of the moraines are outwash plains, spillways and meltwater channels.
As the glacier melted streams of water heavily loaded with rock debris
formed a braided network of streams in front of the ice sheet. Due to
the amount of material in the streams they quickly lost their velocity
dumping sorted rock debris into outwash plains. The coarser material at
the base and the finer sifts and clay at the edges of the plains. These
outwash plains can extend for several kilometres in front of the
moraine.
In Central Ontario the Dummer moraine extends from Gull River to the
Kawartha Lakes. The moraine forms a hummocky terrain consisting of
coarse angular blocks of limestone and large Precambrian boulders. The
matrix is predominantly sand with a faint reddish color from red shale
and has a high total carbonate content. Though these soils are fertile
agricultural has been limited because of physical obstacles thin soil
profiles and excessive boulders.
A very prevalent land feature in Southern Ontario is drumlins, meaning,
“little hill”. Drumlins are smooth elongated hills with blunt noses
that indicate the direction in which the glaciers had advanced and
gentler longer slopes pointing in the opposite direction. Drumlins are
important because they indicate the direction of ice movement. The
process in which drumlins are formed is unclear and they commonly occur
in clusters referred to as drumlin fields.
Encompassing Hastings, Simcoe and Northumberland County the
Peterborough drumlin field covers approximately 1750 square miles; it
is the largest cluster of drumlins in Southern Ontario. Generally the
Peterborough Drumlin field is composed of highly calcareous till but
exceptions do exist. In Victoria County the drumlins are scattered,
bedrock is very close to the surface and there are greater quantities
of angular limestone float. In Peterborough, Northumberland and
Hastings Counties the till has less rock rubble and a significant
increase in Precambrian boulders. To the south and west the drumlin
field contains much more sand and is covered by wind deposited stone
free sift and sand. This layer is normally 2 feet in depth but can have
a depth of six feet in low-lying areas. Between the individual drumlins
clay flats usually occupy the landscape with many swampy areas
intervening.
Generally, the Peterborough drumlin field soils are highly fertile and
though stony are more easily worked than the Dummer moraine. This
stoniness has helped to limit soil erosion but a considerable amount of
topsoil has been lost. Frequent patches of grayish subsoil along the
steeper slopes indicates the loss of topsoil.
As well as drumlins the Peterborough area is also noted for its number
of eskers. Eskers are ridges comprised primarily of well-washed sand
and gravel. It is believed they are formed by the deposition of
sediments by meltwater streams confined to tunnels or channels within
the glacier. The eskers have very little agricultural value and are
exploited for sand and gravel.
The surface geological deposits previously described is the parent
material from which soils in Central Ontario area are formed. It is the
mineralogical characteristics found in the parent material, climate and
vegetative conditions that determine the soil type. Singularly the most
important factor leading to soil and clay formation is the intensity of
hydrolysis.1 Hydrolysis means the amount of water that can pass
unimpeded through the soil solum will result in rapid soil development.
This is true for all the physiographic regions in Central Ontario where
the parent material is predominated by a well-drained sand matrix. An
example is the Bondhead loam found in the south and western parts of
the area where the drumlins are generally flatter. Unlike the shallower
profiles to the north where water is impeded by bedrock these deep
profiles seldom have free carbonates.
The soils in Central Ontario area belong to the Luvisolic order. Soils
of this order generally are light colored and have illuvial
B-horizons2. These soils form in well to imperfectly drained sites
becoming sandy loam to clay. Parent material is usually base-saturated
and calcareous. An important weathering feature in the calcareous soils
of Southern Ontario is the dissolving of calcium carbonate concretions
and nodules in glacial till parent material. This is because CaCO3
maintains a preserving effect and the dissolution of calcium speeds up
the weathering and soil development process.
Gray Brown Luvisols have high biological activity and an abundance of
earthworms. Typically they formed under deciduous and mixed forests in
mild, humid climates. Due to this intense activity leaf litter is
usually incorporated into the soil and humified.
Physiography of Central Ontario — Northern Region
The Algonquin Highlands is the largest physiographic region in Southern
Ontario, representing 15,500 square miles (9,934,000 acres) and is
underlain predominantly by Precambrian granite rocks. There are
frequent outcrops of rock amounting to about 5% of the total area. The
soils are general shallow, stony, sandy and acid. The majority of the
soil in this region is forested mainly because of rock outcrops,
shallow soils and poor fertility. However in parts of Renfrew, Lanark,
Lennox, Addington and Hastings Counties there are farming pockets on
areas of deeper till.
The soils mapped in this region belong to the soil order of Bruises.
Bruises are young poorly developed soils, which are general poor in
exchangeable captions. AMP will be conducting research this year in
forest kill areas within the Algonquin Highlands. Our hypothesis is
tree mortalities are due to naturally low calcium soils becoming
completely exhausted due to acid rain. This results in clay mineral
weathering releasing aluminum and other toxic metals. These add soils
require regular liming to halt progressive acidification and eventual
forest deaths.
Complexity of Central Ontario Landscape
This review of Central Ontario’s bedrock geology, quaternary geology,
physiographic regions and resulting soil development indicates a region
of variability both in landscape and soil mineralogical. This
complexity does not work well with modem agricultural practices but is
ideal for specialty crops and small-scale organic farming.
For organic agriculture to work successfully within a region there are
a number of very key factors that must be present. These factors hinge
on systems complexity. Very diverse ecosystems are more likely to
withstand erratic weather conditions, pathogen encounters and will also
provide an abundance of local resources. The key factors, which make
Central Ontario ideal for small-scale organic farming and specialty
crop production, are:
1. Complexity of Physiographic Regions —the regions of
Central Ontario are extremely diverse.
2. Complexity of Soil Mineralogy — complex soils result in
high quality mineral dense foods.
3. Abundance of Pristine Woodlands — a result of this soil
complexity is that many areas were never cleared for agricultural
purposes and therefore wooded areas are greater then cleared land.
This symbiotic relationship with the abundant woodlands ensures that
soil and associated microbial communities Will be maintained at maximum
diversity. This will ensure that potential pathogen encounters will be
rare and limited. The forests act as a natural plant predator control.
4. Large Flat Capture Basin —If Global warming trends are correct
Central Ontario maybe one of the few jurisdictions in North America
where water requirements can be met with yearly precipitation and
abundant ground water.
5. Natural Resources — the close proximity to rare alkalic
Precambrian rocks, underlying calcium rich sedimentary rocks and
sluggish drainage basins has resulted in the development of abundant
peatlands, nutrient rich mails and basal tills. The key to utilizing
very responsive acid sand soils is sources of inexpensive mineral
inputs. Regions within the Central Ontario Region disregarded because
of very poor nutrient qualities and acidity may prove exceptional sites
for market gardens and other specialty crops.
8. Climate — cold weather is very beneficial to organically
grown crops. Cold weather ensures that many of the potential pathogens
brought in with seed or through farming practices will not survive the
harsh winters.
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