Residual soil nitrogen indicator for agricultural land in Canada

Residual soil nitrogen (RSN) is the amount of inorganic nitrogen that remains in the soil at the end of the growing season after crops have been harvested. RSN is an estimate of this quantity, calculated as the difference between all N inputs (fertilizer, manure-N, biological fixation, and atmospheric deposition) and all N outputs (N removed in crop harvest, N lost from ammonia volatilization and N lost from denitrification) assuming that mineralization and immobilization are generally balanced. RSN was calculated on a soil polygon level (scale 1:1 million) as well as on provincial and national levels for each of the 5 census years from 1981 to 2001. The Canadian average RSN values from 1981 to 1996 were fairly constant with a range of 12.9 to 13.9 kg N ha-1. However, RSN increased by 51% from 13.9 kg N ha-1 in 1996 to 21.0 kg N ha-1 in 2001. This dramatic increase was due to several factors including an increase in legume crop acreage (i.e., increased biological N2 fixation) and lower crop yields and red...