by Theresa Peluso
This year has been dedicated by the UN General Assembly to soil. What exactly is soil, and why is it so important?
The Oxford Dictionary defines “soil” as “the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles”. In addition to these basic components, soil contains water, which provides nutrients to plants, and air, which is needed by the microorganisms in the soil, thereby enabling them to release additional nutrients to plants. Microorganisms are explained in more detail here (information taken from University of California Agriculture and Natural Resources (http://ucanr.org/sites/intvit/files/24453.pdf):
The community of organisms that lives in soil plays many important roles in the successful functioning of agricultural ecosystems. This community consists of bacteria, fungi, protozoa, nematodes (predators of microorganisms and pathogens of plants), earthworms, arthropods, and other organisms. Although certain species are harmful to crops, most are beneficial and even essential for the well-being of plants. There are striking similarities between the roles of microorganisms in the human body and in the soil. (end of quote)
Why is soil important? As explained by the Food and Agricultural Organization of the United Nations (http://www.fao.org/home/en/):
Soil is a finite resource, meaning its loss and degradation is not recoverable within a human lifespan. As a core component of land resources, agricultural development and ecological sustainability, it is the basis for food, feed, fuel and fibre production and for many critical ecosystem services. It is therefore a highly valuable natural resource, yet it is often overlooked. The natural area of productive soils is limited – it is under increasing pressure of intensification and competing uses for cropping, forestry, pasture / rangeland and urbanization, and to satisfy demands of the growing population for food and energy production and raw materials extraction. Soils need to be recognized and valued for their productive capacities as well as their contribution to food security and the maintenance of key ecosystem services. (Date: 03/03/2015)
With the dwindling amount of arable land resulting from the proliferation of housing developments and roads (you have only to look at Kanata, Barrhaven and Manotick for local examples) and the increasing demands put on land to boost production (to feed a growing population and provide a decent income for farmers), our soil is increasingly at risk. Regular application of pesticides, herbicides and synthetic fertilizers, overgrazing, deep ploughing, lack of crop rotation, overcultivation, planting incorrectly, compacting the soil, and removing trees and draining wetlands (which, in combination, help to clean the air, act as carbon sinks, mitigate flooding and reduce wind impacts), all cause long-term damage to soil fertility.
In addition to the threats posed by intensive farming and competing uses, there is also the problem of contamination, of which there are many causes: industrial accidents and accidental spills (such as pipeline leaks); acid rain; road salt; landfill and illegal dumping; mining; inappropriate disposal of hazardous waste; nuclear wastes; drainage of contaminated surface water; untreated sewage, and disposal of coal ash and slag. Finally, there is also the growing problem of extreme weather events resulting from climate change, as a result of which droughts, floods and heat waves increase the danger of soil erosion, and degrade soil structure and nutrient content. Contaminated or polluted soil can cause illness or death in people by exposure through direct contact, inhalation or ingestion of the toxins in groundwater contaminated by soil. Needless to say, it also negatively impacts the flora and fauna that surround us. These contaminants can work their way up the food chain, from the plants and insects that live in the soil, all the way up to those at the top, including us humans.
What are the particularities of soil in Lanark County? Two especially useful sources are: Earth, Water, Fire: An Ecological Profile of Lanark County, written and first published in 1999 by local ecologist Dr. Paul Keddy, and the report A Soil Survey of Lanark County, published in 1961 by the Canada Department of Agriculture and the Ontario Agricultural College. Here’s what I learned:
Lanark County is divided into two regions: the Canadian Shield in the north and west, with predominantly rocky, acidic soils; and the limestone plain in the east and south, with deeper, more alkaline soils. Also, unlike most of the rest of the Canadian Shield, Lanark County has large areas of marble, the result of heat and pressure altering the original limestone. Although the landscape consists of rocky, rolling hills, typical of the Canadian Shield, the soils here are alkaline and more fertile. The presence of marble results in different kinds of forest, better soils for farming, and unusual wetlands. Because the soil on the Canadian Shield is acidic, it is more sensitive to the effect of acid rain; however, it seems that the presence of marble decreases this effect. Generally speaking, deep soil over limestone is not very sensitive to acid rain – with the exception of the sandstones in the limestone plain around Perth, Smiths Falls and west of Mississippi Lake, which are more sensitive than most limestones.
A Soil Survey of Lanark County describes our county’s “surface deposits” as follows:
The unconsolidated surface deposits in Lanark County are of glacial origin (the result of the end of the last ice age, 12,000 years ago), and are the parent material from which soils have developed. The differences that occur in texture, relief and drainage of soils are a result of differences in the nature of these deposits….The surface deposits are commonly referred to as till, outwash, kame, esker, deltaic, drumlin and lacustrine, which denote the mode of deposition and, to some extent, the textural composition of the deposit. Glacial till is non-sorted material, a mixture of broken rock fragments and soil particles that range in size from sand to clay. Glacial till covers a large part of Lanark County.
The till cover is thin over most of the county and in many places the bedrock is exposed. Areas of deeper materials do exist, however; sandy kames are scattered throughout the area west of Mississippi Lake and River. Nowhere do these hilly deposits occupy a large acreage, but they are prominent east of Lanark, around Flower Station and south of Watson’s Comers.
Deep deposits of calcareous sandy loam till occur in a comparatively narrow band from Prestonvale through Ferguson Falls to Clayton. They also occur around Lanark and Perth. Indeed, the region around Perth is exceedingly complex and many different deposits may be found. In addition to the sandy loam tills are small areas of clay loam till, outwash sand, stony acid till, and lacustrine clays. The lacustrine clays have been deposited in the depressions and flats lying between the gently rolling slopes of the other deposits. The largest lacustrine deposits occur east of the Mississippi River between Carleton Place and the border of Renfrew County. Lacustrine deposits are sorted fine-textured materials laid down in still or slowly moving waters and usually have level topography. Level lacustrine deposits occur southeast of Carleton Place and north of Pakenham, but these deposits are much more rolling in the region between these two towns. (end of quote)
The report, obviously written for soil scientists, goes on to classify the soils found in the area. There are at least 14 types, further subdivided into good, imperfect and poor. The “good” subtypes have names like Almonte, Appleton, Elmsley, Grenville, Kars, White Lake and Manotick.
As we can see, the bulk of the soil we have today has taken millions of years to form. Because new soil is formed so very slowly, at a rate of only 1 cm every 100 to 400 years, it is considered a nonrenewable resource. Once destroyed, it is gone for good.
As a follow-up to A Soil Survey of Lanark County, published more than 55 years ago, here are some interesting points from a lecture by soil scientist David Kroetsch, a botanist and ecologist with the Canadian Soil Information Service (Information taken from mvfn.ca, Lecture Report of September 2012 MVFN Lecture, written by Pauline Donaldson):
At this lecture, Kroetsch noted that a survey he had conducted of Lanark County soils showed that the nature of these soils was relatively unchanged with the exception of some areas, which were negatively affected by over-agriculture, addition of fertilizers, drainage of wetlands, and atmospheric pollution. He also explained how, in addition to these human activities, earthworms (which are non-native to Canada) have, in recent times, damaged the soils in forests by consuming the leaf litter (which allows water to penetrate through to the underlying soil and roots) and converting it to castings, which are denser, less permeable, and more prone to erosion.
We can’t get rid of earthworms and, in fact, they do provide benefits in terms of aerating the soil and enriching it with their castings, but there are other actions we can take to sustainably manage and protect our soil. Our federal and provincial governments need to put the teeth back into their environmental legislation to ensure that industries are made to abide by the rules for preventing environmental damage from their activities. Ensuring that farmers get a reliable, decent income from their labour will remove the pressure to maximize yields in the short term while ignoring the need to preserve soil fertility for the long term.
Our municipality already provides facilities for disposal of hazardous and electronic waste, and has partnered with the Rideau Environmental Action League’s Take-It-Back program to enable us to get rid of tires, medication, ink cartridges, and other unwanted items. Check the Town’s website http://www.mississippimills.ca/en/live/otherwastediversionoptions.asp for more information. Other suggested steps are to avoid the use of road salt, and ensure that existing agricultural land, forests and wetlands are protected from competing uses. The Town can also work with concerned citizens to enforce the anti-dumping by-law (no. 10-31).
As individuals, we need to respect the provincial legislation forbidding the cosmetic use of pesticides; pick up litter on roadsides and notify the Town of garbage dumped by idiots in the
ditches; follow the rules for protecting wells and water bodies; safeguard forests, water bodies, and wetlands on our property; garden sustainably; and support and encourage elected representatives who advocate for the natural environment.
For those who grow crops and raise animals, perhaps there is a way to implement sustainable soil management practices, such as ploughing across hills and providing windbreaks, leaving unploughed grass strips between ploughed lands (strip cropping), enriching the soil with humus and ensuring that it always has plants growing in it, avoiding overgrazing, allowing indigenous plants to grow along riverbanks, conserving wetlands and trees, rotating crops, minimizing tillage and use of pesticides, herbicides and chemical fertilizers, encouraging water infiltration, and reducing water runoff.
Especially this year, the International Year of Soils, let’s make a commitment from now on – if we haven’t already – to appreciate our soil and treat it with the respect it deserves.
