Solute dynamics and the Ontario nitrogen index: II. Nitrate leaching

• Published in: Canadian journal of soil science 2016-06, Vol.96 (2), p.122-135
• Main Authors: Drury, C.F., Reynolds, W.D., Parkin, G.W., Lauzon, J.D., Saso, J.K., Zhang, T.Q., Yang, X.M., Tan, C.S., Liu, K., Calder, W., Oloya, T.O., Welacky, T.W., Reid, D.K.
• Format: Article
• Language: English
• ISSN: 0008-4271; 1918-1841
• DOI: 10.1139/cjss-2015-0070

Nitrogen (N) leaching from soil into surface and ground waters is a concern in humid areas of Canada. As a result, N management protocols, including the Ontario N Index, are widely used to identify N leaching risk, although field assessment remains limited. Nitrogen fertilizer and chloride (Cl) tracer were fall-applied to five agricultural soils in Ontario with different textures and hydrologic soil groups (HSG) to assess the Ontario N Index and characterize inorganic N movement over 1 yr. The treatments included three N rates (0, 100, and 200 kg N ha −1 ) plus Cl tracer and 200 kg N ha −1 rate without Cl. After spring thaw, N loss from the crop root zone (top 60 cm) ranged from 68% for Brookston clay loam to 99% for Harrow sandy loam. A strong linear relationship between apparent N recovery and apparent Cl recovery indicated that N loss from the root zone occurred primarily by downward leaching. Leaching was controlled by the minimum measured saturated hydraulic conductivity (K sat ), and good estimates of N leaching were obtained using a quasi-theoretical relationship between N loss and K sat . We concluded that Ontario N Index estimates of N leaching risk might be improved by including site-specific measurements of K sat .