The indicator of risk of water contamination by nitrate-nitrogen

• Published in: Canadian Journal of Soil Science
• Main Authors: De Jong, R., Yang, J Y, Drury, C F, Huffman, E C, Kirkwood, V., Yang, X M
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2007
• Subjects: British Columbia; Canada; Newfoundland
• Online Access: http://dx.doi.org/10.4141/s06-060; http://www.nrcresearchpress.com/doi/pdf/10.4141/S06-060

Drriven by changes in agricultural production practices, nitrogen (N) inputs have increased steadily on Canadian farms. An agro-environmental indicator was developed to monitor potential water pollution by N: indicator risk of water contamination by nitrate-nitrogen (IROWC-N). The indicator links the residual soil nitrogen (RSN) indicator to climate and soil conditions to assess the likelihood of N moving through the soil and out of the agricultural system. The results are assessed in terms of N lost via leached water (N lost ) and its concentration in the leached water (N conc ), with the IROWC-N risk classes based on N lost and N conc criteria. The estimated amount of N lost in Canada ranged from 5.1 kg N ha -1 in 1991 to 6.4 kg N ha -1 in 2001. N conc values remained fairly constant during the 1981 to 1996 census years (ranging from 3.7 to 4.5 mg N L -1 ), but increased sharply (27%) to 5.7 mg N L -1 in 2001 as compared with 1996. During the 1981 to 2001 period, close to 80% of the Canadian farmland area remained in the very low and low IROWC-N risk classes, but over the years 18% shifted to a higher risk class. In 2001, large areas (> 1 million ha) in the high risk IROWC-N class were found in Manitoba, southern and eastern Ontario and in Quebec. Provincial averages of N lost over 5 census years (1981, 1986, 1991, 1996 and 2001) varied from less than 5 kg N ha -1 in Alberta and Saskatchewan to more than 20 kg N ha -1 in Ontario, Quebec and the Atlantic provinces. With the exception of Manitoba, provincial N conc values did not exceed the Canadian drinking water guideline of 10 mg NO 3 -N L -1 . In each of the census years, British Columbia, Alberta and Saskatchewan had more than 70% of the farmland area in the very low and low risk classes for IROWC-N. In Ontario and Quebec, most of the farmland area was either in the low or in the high risk class. More than 50% of the farmland area in New Brunswick, Nova Scotia and Newfoundland was in the very low, low and moderate risk classes, whereas in Manitoba and ...