Soil Quality 101: Land Capability

A reader from Alberta recently asked our illustrious editor for an article around the questions: “What is soil quality? How is it measured? And is there an ideal soil?” Jay then suggested I do a series of articles on the subject so a single article did not get too long winded — as this scribe is often wont to do.

In the first column, we will deal with the concept of “soil” versus “land,” the idea of land capability and talk about the Canada Land Inventory.

SOIL VS. LAND

Soil is the individual square foot or acre of a soil profile, consisting of the topsoil (“A” horizon, in soils jargon), upper subsoil (“B” horizon) and subsoil (“C” horizon.) The depth and nature of the layers depend on the starting point left by the glaciers — soil parent material —and the interaction of climate, drainage and vegetation over the past 10,000 years.

Water is a huge factor. All soils textbooks list the five soil-forming factors as parent material, climate, topography, vegetation and time. In my fourth-year soils class at U of S I told the students the five soil forming factors are water, water, water, water and water to emphasize the importance of water.

A “soil” is an individual piece of the surface of the earth that has similar properties based on the above soil forming factors.

When we are struggling with how to partition parts of a farm field and manage them separately — precision farming —we are actually trying to figure out how to map the individual soils in that land parcel.

Land is the way individual soils are situated on any given piece of real estate. We buy a quarter section of land that often has several different soil types. The capability of that land is the integrated capability of all the parts.

A quarter section of black loam soil on nearly level topography — with just enough slope to spill excess water away in shallow ravines — has a much higher capability for agriculture than the same black loam situated on pothole topography with many sloughs and bluffs.

LAND CAPABILITY

Land capability relates to what we want to use the land for. Canada Land Inventory soil capability maps were created back in the 1960s, ’70s and ’80s. The feds and provinces got together to make the maps based on the land capability for a number of potential land uses, including forestry, recreation, ungulates (deer and such) and waterfowl. They also created agriculture capability maps with seven land classes:

Classes 1 to 3 are arable land. In Saskatchewan, in particular, there is only a bit of Class 1 land — Melfort Silty Clay Loam with no sloughs. Class 2 is Regina and Sceptre Heavy Clay and the like where the fields are square and relatively flat. Class 3 is Weyburn loam and the like with more significant limitations but still arable.

Then you get into land classes that are more suitable to forages and pasture. Class 4 is better suited to forage but in some cases may be viable farmland. Class 5 is suitable for seeded forage. Class 6 is native pasture. Class 7 is not suitable for agriculture of any kind — i. e. water, railways, towns, etc.

The land capability classification is based on limitations: topography, texture, stones, sloughs etc.

Attractive color maps were produced on a National Topographic System base at a scale of 1:250,000. The scale is OK for general use by bureaucrats but not much use at the farm level. The maps are out pf print but if you plug “Canada Land Inventory” into Google, some information comes up but this old fossil was not able to pull much out of it.

A federal government website called NLWIS (National Land and Water Information Service) allows access to soil maps of various scales from across the country. Even I am able to download the Saskatchewan maps and use them so most anyone can.

In Saskatchewan, a series of Soil Capability for Agriculture maps was produced as individual black and white brochures for each rural municipality. They were four pages on 8 by 11 paper, so they are easy to photocopy. Those maps still exist in the Ag Building at U of S and I still use them from time to time.

MAPS NOT USEFUL FOR PRECISION FARMING

The big problem with almost all soil maps on the Canadian Prairies is that the scale of mapping and level of detail is such that they are NOT usable for crop planning at the quarter-section level. Some detailed maps in Manitoba are an exception.

When someone asks me about an individual quarter section, I first consult a topographic map and the soils map. After 46 years of using such maps, the soil map they will tell me if I should look any further. If so, I then consult municipal assessment sheets (available in Saskatchewan only), air photos, and Google Earth. After all that, the only way to add any more info is to inspect the land and make observations and measurements in the field.

So there you have a broad description of land capability. In the next article we will zero in on the individual question and deal specifically with “soil quality.”

J. L. (Les) Henry is a former professor and extension specialist at the University of Saskatchewan.

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