Developing a Canadian Agricultural Nitrogen Budget (CANB v3.0) Model to Predict Residual Soil Nitrogen and Nitrate Leaching Across Canadian Farmland.

The Canadian Agricultural Nitrogen Budget model (CANB v3.0) was developed to estimate two Agri-environmental Indicators; Residual Soil Nitrogen (RSN) and the Indicator of Risk of Water Contamination by Nitrogen (IROWC-N) at the 1:1 million spatial scales. The RSN (kg N ha^-1) is an estimate of the amount of N remaining in the soil after crop harvest. The IROWC-N provides an estimate of the concentration and amount of nitrate-N leaching from the rooting depth of the soil.

In the CANB v3.0 model, fertilizer N application was reconciled with provincial N sales. Storage and land losses of manure N and manure N mineralization were estimated. Biological N₂ fixation rates were adjusted by crop yields and crop N removals were estimated by crop yield and N concentration in the yield and biomass. N leaching losses in both growing and non-growing seasons were estimated by integrating the growing and non-growing drainage volumes from the daily IROWC-N model with the CANB v3.0.

Regional differences in the RSN were large. The average RSN values were less than 30 kg N ha^-1 in western Canada but greater than 66 kg N ha^-1 in eastern Canada. There was an increase in the amount of land in the high and very high RSN risk classes in Canada from 1981 (10%) to 2001 (30%) followed by a decrease to 17% by 2006.

Annual (growing and non-growing seasons) N leaching losses varied from 2.6 kg N ha^-1 in 1981 to 3.7 kg N ha^-1 in 2006, and average nitrate concentrations increased from 2.0 mg N L^-1 in 1981 to 7.0 mg N L^-1 in 2006. These results demonstrate that there is an increasing risk of RSN and IROWC-N over time in Canadian farmland and yearly climatic variability can accentuate these differences.

Keywords: Fertilizer N, manure N, biological N₂ fixation, residual soil N, nitrate leaching, Canadian Agricultural Nitrogen Budget (CANB) model