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Technical Thematic Report No. 15. -Trends in residual soil nitrogen for agricultural land in Canada, 1981 2006

National perspective

The RSN levels varied across Canadian farmland in 2006 from the very low risk class (0 to 9.9 kg N/ha) to high risk class (>40  kg N/ha) (Figure 1). The agricultural land in the Prairies Ecozone+ was split primarily between the very low risk and low risk classes. The inputs are somewhat limited as a result of the lower yield potential in this dryland environment. Agricultural land in the Boreal Plains Ecozone+ presents a medium to very high risk areas in both central Alberta and the eastern regions of this ecozone+ (central Manitoba). The southern areas of both the Pacific Maritime and Western Interior Basin ecozones+ were generally in the very high risk class with RSN levels exceeding 40 kg N/ha. The Montane Cordillera Ecozone+ has both low and medium risks area in southwest areas of British Columbia but agricultural land in central British Columbia was primarily in the low risk class. The Boreal Shield Ecozone+ covers a wide geographic area and the RSN risk class is generally in the very high risk class in central Manitoba and the regions north of the St. Lawrence lowlands. The south central regions in the Boreal Shield are characterized as having soils in the medium to high risk classes. For the Mixedwood Plains Ecozone+ the RSN ranges from very low and low risk classes in southwestern Ontario to medium to very high risk classes in the north and eastern portions of the ecozone+. The agricultural land in the Atlantic Maritime Ecozone+ was primarily in the very high risk class, although areas of northern New Brunswick and southwestern Prince Edward Island had polygons in the medium risk class. The agricultural land in the mid-western and northern regions of the Newfoundland Boreal Ecozone+ was in the very high risk class whereas the southeastern areas ranged from very low to the high risk class.

There were 61.4 million ha of agricultural landFootnote6 in Canada distributed amongst 3,285 SLC polygons in 2006 (Table 1). The nitrogen inputs increased steadily from 42.7 kg N/ha in 1981 to 66.9 kg N/ha in 2006 (Table 2). In 1981, the nitrogen inputs from fertilizer (15.2 kg N/ha) and from nitrogen fixation from legumes (15.9 kg N/ha) were quite similar and both were greater than the nitrogen input from manure (8.9 kg N/ha) (Table 3). Nitrogen inputs for all three sources increased over time and in 2006 the N input to soils was 25.1, 28.3, and 10.8 kg N/ha respectively (Table 3). Nitrogen outputs also increased across Canada over time from 33.4 kg N/ha in 1981 to 49.1 kg N/ha in 2006 primarily as a result of increased crop yields (Table 2). The net result was that the RSN levels also increased from 9.3 kg N/ha in 1981 to a maximum of 25.0 kg N/ha in 2001 followed by a decrease to 17.8 kg N/ha in 2006. The 2001 drought in many areas of Canada contributed to lower yields and nitrogen uptake values which left more nitrogen in the soil after harvest. Producers add fertilizer and manure based on the expectation of an average or above average growing season and expectation of average to above average yields.

Table 1. The agricultural land area and number of Soil Landscape of Canada polygons in Canada by ecozones+, 2006.
Ecozone+Number of SLC polygonsAgricultural land area (thousands of ha)
Pacific Maritime108203
Western Interior Basin104593Footnote[1]
Montane Cordillera2001,163
Taiga Plains59
Boreal Plains60512,053
Boreal Shield251920
Mixedwood Plains4695,338
Atlantic Maritime5141,130
Newfoundland Boreal4421



Footnote [1]

The agricultural land area reported here for the Western Interior Basin is greater than that reported in the ESTR wildlife habitat capacity report (Javorek and Grant, 2011). This discrepancy can be attributed to the methodology used to maintain the anonymity of the data. See the Agri-environmental indicators section on page 1.

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Table 2. Nitrogen input, output, and residual soil nitrogen (RSN) for Canadian ecozones+ that contain agricultural land, 1981 to 2006.

Nitrogen input (kg N/ha)
Pacific Maritime93.010697.299.7110103
Western Interior Basin59.755.350.751.756.641.8
Montane Cordillera52.951.350.449.651.444.8
Taiga Plains27.
Boreal Plains40.846.450.862.069.769.3
Boreal Shield82.495.191.898.6109107
Mixedwood Plains123139138143149153
Atlantic Maritime95.8110108122132137
Newfoundland Boreal50.783.572.7115106102


Nitrogen output (kg N/ha)
Pacific Maritime50.652.653.249.846.746.0
Western Interior Basin39.134.632.731.432.025.4
Montane Cordillera39.536.937.
Taiga Plains23.831.728.432.537.235.6
Boreal Plains32.738.140.343.443.347.2
Boreal Shield62.673.162.470.165.674.0
Mixedwood Plains80.
Atlantic Maritime68.178.064.681.973.481.4
Newfoundland Boreal30.642.340.667.352.148.4


Residual soil nitrogen (RSN) (kg N/ha)
Pacific Maritime42.453.444.049.963.357.0
Western Interior Basin20.620.718.020.324.616.4
Montane Cordillera13.414.413.316.620.215.8
Taiga Plains3.
Boreal Plains8.18.310.518.626.422.1
Boreal Shield19.822.029.428.543.433.0
Mixedwood Plains42.952.047.847.062.841.0
Atlantic Maritime27.732.043.440.158.655.6
Newfoundland Boreal20.

Table 3. Nitrogen input from manure, fertilizer, and nitrogen fixation by leguminous crops for Canadian Ecozones+ that contain agricultural land, 1981 to 2006.

Manure nitrogen inputFootnote[1] (kg N/ha).
Pacific Maritime49.254.252.552.854.956.1
Western Interior Basin17.815.216.317.116.713.5
Montane Cordillera15.113.714.415.013.611.7
Taiga Plains4.
Boreal Plains6.
Boreal Shield19.220.820.620.820.720.3
Mixedwood Plains28.528.227.327.126.726.6
Atlantic Maritime30.332.
Newfoundland Boreal23.842.432.045.140.934.5


Fertilizer nitrogen input (kg N/ha)
Pacific Maritime17.
Western Interior Basin12.
Montane Cordillera8.
Taiga Plains8.915.
Boreal Plains15.119.218.826.026.225.8
Boreal Shield15.520.821.720.823.521.3
Mixedwood Plains40.
Atlantic Maritime21.728.331.331.935.636.4
Newfoundland Boreal11.318.317.521.719.928.1


Nitrogen fixationFootnote[2] (kg N/ha)
Pacific Maritime24.623.324.823.926.526.4
Western Interior Basin27.927.525.223.927.421.7
Montane Cordillera27.125.926.825.026.524.5
Taiga Plains12.114.412.520.027.435.3
Boreal Plains16.818.622.424.731.631.1
Boreal Shield41.647.543.551.059.359.8
Mixedwood Plains47.453.259.765.271.176.0
Atlantic Maritime39.645.340.054.360.363.9
Newfoundland Boreal13.620.921.246.343.337.7


Footnote [1]

Manure nitrogen input represents the net amount of mineral nitrogen applied to the soil or released from the mineralization of organic nitrogen over three years

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Footnote [2]

Legume nitrogen fixation represents the biologically fixed nitrogen from legume residues that become available in the soil in the first year after plowing as well as the N mineralized from legume residues incorporated into the soil in the previous years.

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When both land area and RSN estimates were considered on a national basis, there were about 565,000 tonnes of inorganic nitrogen remaining in Canadian soils following harvest in 1981. This increased 2.7 fold to 1.52 million tonnes in 2001. It then decreased to 1.06 million tonnes in 2006 primarily as a result of increased nitrogen outputs compared to nitrogen inputs, reflecting higher crop yields during the latter 5-year period. Nevertheless, the 2006 levels of inorganic nitrogen remaining in Canadian soils were still about twice as high as the 1981 levels. This model does not account for changes in soil organic matter. If soil organic matter were to have increased, then some of this RSN may have been immobilized and converted to soil organic nitrogen.

The risk of loss of RSN (especially nitrate) to the environment is a function of the amount, timing, and nature (rain versus snow) of precipitation in the particular region as well as the antecedent soil moisture contents. Humid regions such as those found in central and eastern Canada as well as coastal British Columbia would be at a greater risk of nitrate loss than the drier regions such as the Canadian prairies (Prairies and Boreal Plains ecozones+).


Footnote 6

Agricultural land, as discussed in this report, does not include the “All Other Land” category from the Census of Agriculture. See the Agri-environmental indicators section on page 1 of this report for an overview of the land included in the analysis for each of the three ESTR Technical Thematic Reports on agri-environmental indicators.

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