LFS:UBC Farm Audio Tour 7 Soils

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Soil quality (or health) is an important determinant of a farm’s sustainability and its ability to function productively in a landscape AND maintain a healthy environment. In addition to the requirements of the local market for vegetables and fruit, the nature of its soils drives UBC Farm management practices.

Soils anywhere are a product of the action of climate and biota (plants, animals and microorganisms) on the original parent material over a period of time and are influenced by their position in the landscape, topography. While we are standing in the UBC Farm landscape, let’s consider what the soils and the factors influencing their formation tell us about the natural history of the southwest corner of the Point Grey peninsula.

Climate The humid maritime climate in the UBC Farm’s region is unique in Canada as it has a long, moderately warm, frost free period, heavy winter rainfall, summer drought and minimal freeze-thaw action. As a result, our soils are highly leached of basic elements such as calcium, magnesium and potassium. The reddish brown colours of the subsurface soil, known as a B horizon, reflect the leaching of iron out of the soils’ surface or A horizon and redeposition deeper in the soil.

Biota Soil formation has been the result of the dominance of coniferous trees and associated understory vegetation on the nature and quality of the organic matter added to these soils, much of which is contained in litter layers at the soil surface. For a first hand view of this forest ecosystem now in its second growth after the initial logging of the old growth forest, take a walk on the agroforestry trail that begins just to the west of the Farm Centre. The cultivated areas of the farm have soils that are greatly modified, at least in their upper 15 to 30 cm, from their native state by the change to agricultural crops, and additions of lime, manures, compost and fertilizers.

Parent Material Picture in your mind a glacier reaching a height of 1.5km above the current soil surface and that 8 to 10 thousand years ago we would be standing at about sea level. This glacial action “bulldozed” mineral materials from the direction of the north shore mountains. Subsequent washing by vast quantities of glacial melt water and then wave action by sea water, have left behind a geological deposit characterized by stoniness and a lack of silts and clays, most of which were washed into the Salish Sea, also known as the Strait of Georgia. A process known as isostatic rebound has resulted in an increase in the elevation above sea level of Point Grey subsequent to the retreat of the glaciers. Find a cultivated area of the Farm and pick up a handful of soil. Note the gritty feel that results from the dominance of sands and gravel left behind by the site’s glacial history and which formed the mineral or parent material in which the Farm’s soils formed.

Topography The UBC Farm is situated on a southwest slope and you can envision a series of three “benches” alternating with sloping areas as you move down the slope. This landscape has influenced soil development and now influences its management. The slopes are subject to soil erosion, if left unvegetated overwinter and, most importantly, the soil drainage is more restricted at the lower elevations of the Farm. Restricted drainage influences the nature of the vegetation and also reduces the intensity of leaching and soil weathering.

Time As in most of Canada, the UBC Farm soils are relatively young, dating back to less than 10,000 years and the recession of the glaciers. Despite this short time, the moist , mild climate and coarse nature of the parent materials have resulted in some intense weathering as expressed by the reddish brown colours at depth in UBC Farm soils.

In summary, the UBC Farm native soils are the result of a moist mild climate and a coniferous forest ecosystem acting on sandy, gravelly and stony parent materials over a period of about 8,000 years since the recession of the last glacier. Human management subsequent to land clearing in the late 1960s has greatly modified the surface or soil A horizon of the native soil to create a more favorable growing medium for agricultural crops. The soils’ coarse nature is, however, still a factor in management as these soils are droughty in summer and require irrigation and nutrients are easily leached over winter. On the positive side, the upper parts of the farm landscape are well drained and can be used during rainy conditions without serious damage to soil structure when we are extending the growing season. Feel free to wander the Farm landscape and think about how the site’s natural history as expressed in its soils influence both farm and forest management.