Station #5 Soil Erosion! From Dust Bowl to Now

Transcription

1 Station #5 Soil Erosion! From Dust Bowl to Now

2 Poor agricultural practices and years of sustained drought caused the Dust Bowl. Plains grasslands had been deeply plowed and planted to wheat. During the years when there was adequate rainfall, the land produced bountiful crops. But as the droughts of the early 1930s deepened, the farmers kept plowing and planting and nothing would grow. The ground cover that held the soil in place was gone. The Plains winds whipped across the fields raising billowing clouds of dust to the skys. The skys could darken for days, and even the most well sealed homes could have a thick layer of dust on furniture. In some places the dust would drift like snow, covering farmsteads. Figure #1 US-Canada Dust Bowl 1930s! Cyclical drought! Botched dry-farming techniques! Depressed economy

3 Perhaps the most vivid depiction of the dust-blowing on the Canadian Prairies in the 1930s is supplied by Gray (1996, p. 11) as follows: Blowing topsoil drifted like snow across the railway tracks in Alberta. It blew from the poor land onto the good land in Saskatchewan and kept Regina, Moose Jaw and Swift Current coated with dust inside and out. It bathed Winnipeg in a perpetual yellow overcast. Roads made impassable by snowdrifts in the winter were drifted into impassibility again with blowing topsoil in the summer. The drifts built up till they covered the fences, choked out the shelterbelts and gardens, reached the roofs of the chicken houses, blew in through the cracks around the farmhouse windows and under farmhouse doors to drive the inhabitants out of their houses and out of the country. Figure #2

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5 Pie Chart of the Uses of Wheat in Canada (crop year 1996 to 1997) Source: Canada. Statistics Canada. Cereals and Oilseed Review, Catalogue no XPB Figure #4

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7 SOIL EROSION SODU - An excellent acronym to remember the way farmers cause soil erosion. Farming practices which cause soil erosion: Problems Description Solution Soil exhaustion Overgrazing Deforestation Up and down ploughing Too many crops are grown on the same area of land. Nutrients are exhausted. Vegetation will no longer grow. Soil exposed to wind and rain. Too many animals are kept on an area of land, vegetation cover is removed, wind and rain erode the soil Farmers remove woodlands and hedgerows. Less protection from the wind and rain lead to increase in erosion. This is when farmers plough up and down hills. Rainfall flows down furrows removing top soil. Crop rotation - farmers should grow different crops from year to year. Fields should be taken out of production to allow the recovery of nutrients. Rotate animals on different fields. Afforestation - planting trees. Farmers should plough following contours. Figure #6

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11 Primary Document on Soil Erosion THE IMPORTANCE OF PLANTS Plants provide protective cover on the land and prevent soil erosion for the following reasons: * plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground; * plant roots hold the soil in position and prevent it from being washed away; * plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode; * plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion. The loss of protective vegetation through deforestation (see Enviro Facts "Deforestation"), over-grazing, ploughing, and fire makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life - this process is called desertification (see Enviro Facts "Desertification"). It is very difficult and often impossible to restore desertified land. Figure #10

12 Fertilizer consumption (kg per capita/year) r trends in three major agricultural variables: agricultural area, irrigated area and per capita fertilizer consumption. Fertilizer consumption has fallen in Europe and North America but - elsewhere m FAOSTAT 2001 and United Nations Population Division 2001 Figure #11

13 Figure #12 "The threat of nuclear weapons and man's ability to destroy the environment are really alarming. And yet there are other almost imperceptible changes - I am thinking of the exhaustion of our natural resources, and especially of soil erosion - and these are perhaps more dangerous still, because once we begin to feel their repercussions it will be too late." (p144 of The Dalai Lama's Little Book of Inner Peace: 2002, Element Books, London)