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

Ecozone+ results

There are ten ecozones+ that have more than 5% of their land area in agricultural production in any one soil landscape of Canada(SLC) polygon. They are: Pacific Maritime, Western Interior Basin, Montane Cordillera, Taiga Plains, Boreal Plains, Prairies, Boreal Shield, Mixedwood Plains, Atlantic Maritime, and Newfoundland Boreal. These will be referred to as “agricultural ecozones+”. The RSN Indicator was estimated for these ten ecozones+ from 1981 to 2006.

Pacific Maritime Ecozone+

There were 203,000 ha of agricultural land distributed amongst 108 SLC polygons in the Pacific Maritime Ecozone+ in 2006 (Table 1). The Pacific Maritime contains only 0.33% of the agricultural land in Canada and most of this is located along the coastal areas of southern British Columbia (Figure 1). The nitrogen inputs increased from 93.0 to 110 kg N/ha from 1981 to 2001, followed by a decrease to 103 kg N/ha in 2006 (Table 2). Manure is the greatest nitrogen source in this ecozone+ with inputs increasing from 49.2 kg N/ha in 1981 to a maximum of 56.1 kg N/ha in 2006 (Table 3). In 2006, the nitrogen inputs from legume fixation (26.4 kg N/ha) and fertilizer addition (18.1 kg N/ha) were each less than half of the input from manure (56.1  kg N/ha). The nitrogen outputs fluctuated between 46.0 and 53.2 kg N/ha over the six census years with the variation primarily due to fluctuating yields and crop nitrogen removal, although changes in crop type may also have contributed to the variation. The RSN values also varied over time with the lowest value of 42.4 kg N/ha in 1981 and the maximum of 63.3 kg N/ha in 2001. The 2001 RSN maximum in the Pacific Maritime Ecozone+ was greater than the RSN values for all other ecozones+ and across all six census years. The high RSN level in 2001 was due to a combination of increasing inputs from manure (from 49.2  kg N/ha in 1981 to 54.9 kg N/ha in 2001), fertilizer (from 17.2 kg N/ha in 1981 to 26.6 kg N/ha in 2001), and legume nitrogen fixation (from 24.6 kg N/ha in 1981 to 26.5 kg N/ha in 2001), while the crop outputs decreased from 50.6 kg N/ha in 1981 to 46.7 kg N/ha in 2001. The decrease in crop outputs was due to a combination of factors including changes in crop areas and decreasing hay yields. Pasture land area decreased from 64% in 1981 to 55% in 2001, while increases in acreage occurred for alfalfa (3% increase), forage crops (2% increase), fruits and vegetable crops (2% increase,) and cereal crops (1% increase).

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Western Interior Basin Ecozone+

The Western Interior Basin Ecozone+ is the smallest (Figure 1) of the agricultural ecozones+; however, there is more agricultural land in this ecozone+ (593,000 ha) than the Pacific Maritime (203,000 ha), Taiga Plains (9,000 ha), and Newfoundland Boreal (21,000 ha) (Table 1). The agricultural land in the Western Interior Basin Ecozone+ is located in 104 SLC polygons. The nitrogen inputs generally decreased over time from 59.7 kg N/ha in 1981 to 41.8 kg N/ha in 2006 (Table 2), although higher nitrogen inputs were observed in 2001 (56.6 kg N/ha) compared to the earlier (1996) or later (2006) census years. The decrease in nitrogen inputs from 2001 to 2006 was due to a combination of decreasing livestock numbers and manure (nitrogen inputs from livestock decreased from 16.7 to 13.5  kg N/ha), decreasing fertilizer nitrogen inputs (from 10.4 to 4.7 kg N/ha), and decreasing nitrogen fixation by legumes (from 27.4 to 21.7 kg N/ha) (Table 3). The nitrogen outputs also decreased over time from 39.1 kg N/ha in 1981 to 25.4 kg N/ha in 2006. This decrease was due to several factors including changing crop acreages and decreasing hay yields. The area of unimproved pasture increased from 60 to 79% while the area of improved pasture decreased from 18 to 5%. Crop yields and nitrogen output were higher for improved pasture compared to unimproved pasture. The net result was that the Western Interior Basin Ecozone+ was the only agricultural ecozone+ where the RSN in agricultural land decreased over time (from 20.6 kg N/ha in 1981 to 16.4 kg N/ha in 2006).

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Montane Cordillera Ecozone+

There were 200 SLC polygons representing 1.163 million ha of agricultural land (1.9% of agricultural land in Canada) in the Montane Cordillera Ecozone+ in 2006 (Table 1). Most of the agricultural land in this ecozone+ is located in British Columbia and southwestern Alberta. The nitrogen inputs remained fairly constant from 1981 to 2001 with a range from 49.6 to 52.9 kg N/ha however there was a substantial decrease in nitrogen input from 51.4 kg N/ha in 2001 to 44.8 kg N/ha in 2006 (Table 2). This decrease was due to a combination of decreased manure inputs (from 13.6 to 11.7  kg N/ha), decreased fertilizer additions (from 9.3 to 6.6 kg N/ha), as well as a decreased legume crop acreage and nitrogen fixation (from 26.5 kg N/ha to 24.5  kg N/ha) (Table 3). The level of nitrogen inputs was similar to that observed for the Western Interior Basin. The nitrogen outputs generally decreased over the 25 years from 39.5 to 29.0 kg N/ha which is in contrast to the trends observed in all other agricultural ecozones+ except for the Western Interior Basin and the Pacific Maritime. The decreased nitrogen outputs were due to an increase in unimproved pasture area (62% in 1981 to 71% in 2006) as well as a decrease in both improved pasture (from 14% in 1981 to 10% in 2006) and forage crop area (from 12% in 1981 to 7% in 2006). The net effect of the changes in nitrogen inputs and outputs were generally increasing RSN values from 13.4 kg N/ha in 1981 to a maximum of 20.2 kg N/ha in 2001 followed by a decrease to 15.8 kg N/ha in 2006.

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Taiga Plains Ecozone+

The Taiga Plains Ecozone+ contained the smallest agricultural area (9,000 ha) and the fewest number of SLC polygons (5) of all agricultural ecozones+ in Canada in 2006 (Table 1). The agricultural polygons are located strictly in the northern portions of British Columbia and Alberta (Figure 1). In 1981, both the nitrogen input (27 kg N/ha) and the nitrogen output (23.8 kg N/ha) were very low and the difference between the two (that is, the RSN) was only 3.2 kg N/ha (Table 2). The nitrogen input doubled over a 25-year period and was 56.8 kg N/ha by 2006 whereas the nitrogen output increased by about 50% over the 25 years to 35.6 kg N/ha. Hence there was about a seven fold increase in RSN to 21.2 kg N/ha by 2006 as N outputs increased at a lower rate than N inputs. These data indicate that too little nitrogen was applied to the crops in 1981 but with the two-fold increase in nitrogen addition over 25 years, only about 40% was removed in the harvested portion of the crop. Nevertheless, the 2006 RSN values (21.2 kg N/ha) in the Taiga Plains were similar to those in the Boreal Plains (22.1 kg N/ha) and considerably lower than agricultural ecozones+ in eastern Canada (33.0 to 55.6 kg N/ha).

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Boreal Plains Ecozone+

The Boreal Plains Ecozone+ contained the second largest area of agricultural land in Canada in 2006 (19.6%) at 12.053 million ha found in 605 SLC polygons (Table 1). The nitrogen inputs steadily increased over time with 40.8 kg N/ha in 1981 to 69.3 kg N/ha in 2006 (Table 2). In 1981, both fertilizer nitrogen (15.1 kg N/ha) and legume nitrogen fixation (16.8 kg N/ha) were greater sources of nitrogen than applied manure (6.7 kg N/ha) (Table 3). Over the 25-year period, all three nitrogen sources increased primarily as a result of increasing legume acreage and livestock numbers, with the largest increases with nitrogen fixation to 31.1 kg N/ha which was about three times greater than the nitrogen input from manure (10.2 kg N/ha) and about 20% greater than nitrogen fertilizer (25.8 kg N/ha) in 2006. The nitrogen outputs also increased from 32.7 to 47.2 kg N/ha over the 25-year period. The RSN values were very low in 1981 at 8.1 kg N/ha and they increased over three-fold to a maximum of 26.4 kg N/ha in 2001, followed by a slight decrease to 22.1 kg N/ha in 2006.

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Prairies Ecozone+

The Prairies Ecozone+ contained the largest amount of agricultural land at 39.945 million ha which was 65% of the agricultural land in Canada (Table 1). The nitrogen inputs were on average lower than all other ecozones+ with 27.6 kg N/ha in 1981 and increasing to 52.5 kg N/ha in 2006 (Table 2). The major nitrogen input in 2006 was fertilizer nitrogen (23.0 kg N/ha) followed by legume nitrogen fixation (19.6 kg N/ha) with manure being the lowest of these sources at 7.8 kg N/ha. The nitrogen outputs steadily increased over the 25 years from a low of 24.3 kg N/ha in 1981 to a maximum of 40.7 kg N/ha in 2006. These increases were due to a combination of increased crop yields as well as decreased areas of summer fallow. However, in 2001, the nitrogen output (32.6 kg N/ha) was lower than either 1996 (35.1 kg N/ha) or 2006 (40.7 kg N/ha) as a result of the widespread drought. Yearly variations in precipitation contribute to the variability in nitrogen output and therefore RSN. The nitrogen outputs increased at a lower rate than the nitrogen inputs and the RSN increased from a low of 3.3 kg N/ha in 1981 to a high of 18.0 kg N/ha in 2001, and then decreased to 11.8 kg N/ha by 2006. Nevertheless, the Prairies Ecozone+ had the lowest RSN of all agricultural ecozones+ in 2006 (Table 2).

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Boreal Shield Ecozone+

The Boreal Shield Ecozone+ is the largest terrestial ecozone+ (Figure 1); however, it contains a relatively small amount of agricultural land at 920,000 ha (abput 1.5% of agricultural land in Canada) distributed amongst 251 SLC polygons (Table 1). The nitrogen inputs were 82.4 kg N/ha in 1981, increasing to 109 kg N/ha in 2001, and then declining slightly to 107 kg N/ha in 2006 (Table 2). The majority of the nitrogen inputs in 2006 were from legume crops (59.8 kg N/ha) followed by fertilizer (21.3 kg N/ha) and manure (20.3 kg N/ha) (Table 3). It should be noted that manure nitrogen inputs remained fairly constant from 1981 to 2006 whereas both fertilizer and legume inputs increased by 37 and 44%, respectively. The increase in N2 fixation was due to the increasing acreage of legume crops over the 25-year period. The nitrogen outputs increased from 62.6 to 74.0 kg N/ha from 1981 to 2006. The RSN increased more than two-fold from a low of 19.8 kg N/ha in 1981 to a maximum of 43.4 kg N/ha in 2001 followed by a decrease to 33.0 kg N/ha in 2006.

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Mixedwood Plains Ecozone+

The Mixedwood Plains Ecozone+ contained 5.338 million ha of agricultural land distributed amongst 469 SLC polygons in 2006 (Table 1). The agricultural productivity of this area is very high as a result of warmer temperatures resulting from the moderating influence of the Great Lakes, particularly for southwestern Ontario, as well as higher precipitation rates. As a result, the nitrogen inputs are the greatest among all ecozones+ (Table 2). The yield potential of this region is achieved as long as there are sufficient nutrients such as inorganic nitrogen available to meet the crop requirements. Since most of the nutrients in the harvested crop are removed every year, additional nutrient inputs are required to ensure that they do not become limiting to crop growth. In 1981, it was estimated that 123 kg N/ha was added to agricultural land and the nitrogen inputs steadily increased to 153 kg N/ha in 2006. Nitrogen outputs primarily in crop yields and nitrogen uptake were also the greatest across all ecozones+ with an estimated output of 80.1 kg N/ha in 1981 which increased to a maximum of 112 kg N/ha in 2006. It should be noted that 2001 output was considerably lower than the outputs in 1996 and 2006 as this was primarily due to a drought in 2001 which reduced crop yields and nitrogen uptake. The RSN values were very high with 42.9 kg N/ha remaining in the soil in 1981 and 41.0 kg N/ha remaining in the soil after harvest in 2006. The RSN reached a maximum of 62.8 kg N/ha in 2001, the drought year. RSN levels in the Mixedwood Plains were similar to those in the Pacific Maritime with the exception of 2006 where the RSN in the Mixedwood Plains (41.0 kg N/ha) were considerably lower than those in the Pacific Maritime (57.0 kg N/ha). Legume nitrogen fixation was the dominant nitrogen source for the Mixedwood Plains and the nitrogen input from fixation increased from 47.4 kg N/ha in 1981 to 76.0 kg N/ha by 2006 as a result of increased acreages of legume crops such as soybean. The nitrogen input from fertilizer remained fairly constant over the 25 years with a range of 40.2 to 50 kg N/ha. Manure additions slightly decreased over 25 years from 28.5 kg N/ha in 1981 to a low of 26.6 kg N/ha in 2006 as a result of declining livestock numbers and manure production.

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Atlantic Maritime Ecozone+

The Atlantic Maritime Ecozone+ had a comparatively small agricultural land area (1.13 million ha) distributed amongst 514 SLC polygons in 2006 (Table 1). The nitrogen inputs were the second highest of all agricultural ecozones+ on a per hectare basis (Table 2). Nitrogen inputs increased from 95.8 kg N/ha in 1981 to a maximum of 137 kg N/ha in 2006. The inputs from legume nitrogen fixation were greater than from either manure or fertilizer addition with 39.6 kg N/ha added through fixation in 1981, which increased to 63.9 kg N/ha by 2006 as a result of increased legume acreage (Table 3). Manure nitrogen inputs remained fairly constant over the 25 years ranging from 30.3 kg N/ha in 1981 to 32.9 kg N/ha in 2006. Fertilizer nitrogen inputs increased steadily from 21.7 kg N/ha in 1981 to a maximum of 36.4 kg N/ha in 2006. There was quite a bit of fluctuation in nitrogen outputs over this period probably due to variations in crop yield and nitrogen uptake. Nitrogen output ranged from a low of 64.6 kg N/ha in 1991 to a high of 81.9 kg N/ha in 1996. The RSN in the Atlantic Maritime increased from 27.7 kg N/ha in 1981 to a maximum of 58.6 kg N/ha in 2001 followed by a slight decrease to 55.6 kg N/ha in 2006. In 2006, the Atlantic Maritime had the second highest RSN value of all agricultural ecozones+; second only to the Pacific Maritime at 57.0 kg N/ha.

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Newfoundland Boreal Ecozone+

The Newfoundland Boreal Ecozone+ contained the second smallest area of agricultural land (21,000 ha distributed into 44 SLC polygons) of the agricultural ecozones+ in 2006 (Table 1). The nitrogen inputs increased by about 2.3 times over fifteen years (from 50.7  kg N/ha in 1981 to 115 kg N/ha in 1996) and then gradually decreased to 102 kg N/ha in 2006, which was twice the 1981 level (Table 2). Manure nitrogen was the greatest source of nitrogen in 1981 at 23.8 kg N/ha compared to 11.3 kg N/ha for fertilizer and 13.6 kg N/ha for legume nitrogen fixation; however by 2006, legume fixation (37.7 kg N/ha) and manure addition (34.5 kg N/ha) contributed similar amount of nitrogen to agricultural land with fertilizer being the lowest of these three sources at 28.1 kg N/ha (Table 3). The nitrogen outputs increased from 30.6 kg N/ha in 1981 to a maximum of 67.3  kg N/ha in 1996 and then decreased to 48.4 kg N/ha in 2006. The increase in nitrogen outputs from 1981 to 2006 was due primarily to changes in crop areas. For example, unimproved pasture area decreased from 65% in 1981 to 46% in 2006, while forage crop areas increased from 12 to 23%, alfalfa increased from 1 to 6%, and cereal crop areas increased from 2 to 5%. The RSN levels generally increased over time from a low of 20.1 kg N/ha in 1981 to a maximum of 53.9 kg N/ha in 2001 which levelled off to 53.6 kg N/ha in 2006.

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