Technical Thematic Report No. 15. -Trends in residual soil nitrogen for agricultural land in Canada, 1981 2006
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.
|Ecozone+||Number of SLC polygons||Agricultural land area (thousands of ha)|
|Western Interior Basin||104||593Footnote|
- Footnote 
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.
Table 2. Nitrogen input, output, and residual soil nitrogen (RSN) for Canadian ecozones+ that contain agricultural land, 1981 to 2006.
|Western Interior Basin||59.7||55.3||50.7||51.7||56.6||41.8|
|Western Interior Basin||39.1||34.6||32.7||31.4||32.0||25.4|
|Western Interior Basin||20.6||20.7||18.0||20.3||24.6||16.4|
Table 3. Nitrogen input from manure, fertilizer, and nitrogen fixation by leguminous crops for Canadian Ecozones+ that contain agricultural land, 1981 to 2006.
|Western Interior Basin||17.8||15.2||16.3||17.1||16.7||13.5|
|Western Interior Basin||12.0||10.7||7.3||8.7||10.4||4.7|
|Western Interior Basin||27.9||27.5||25.2||23.9||27.4||21.7|
- Footnote 
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
- Footnote 
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.
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.
- Date Modified: