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

Abstract

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 .

Long‐term Cropping Effects on Partitioning of Water Flow and Nitrate Loss between Surface Runoff and Tile Drainage

“…Residual N from the previous season is unlikely to be the primary contributor of these nitrate concentrations. Drury et al (2016) found that 79% of fall applied inorganic N (200 kg N ha −1 ) on a Brookston clay loam was lost from the 0‐ to 60‐cm soil profile by spring thaw. The 5‐yr FWM concentration was highest in RC‐F at 10.5 mg NO 3 − –N L −1 , exceeding the Canadian drinking water limit (10 mg NO 3 − –N L −1 ; Health Canada, 2013; Table 2).…”

Climate change impacts on crop yield, soil water balance and nitrate leaching in the semiarid and humid regions of Canada

“…Although a series of environmental policies were adopted and contributed to decreasing N losses, the nitrate concentrations in groundwater and surface waters were still high, which threatened human health and water quality. In Canada, modelling studies on residual soil nitrogen (RSN) and nitrate leaching in farmland from 1981 to 2011 have been conducted [ 32 , 33 ]. Annual RSN levels (i.e., annual RSN = N input–N output) increased from 9.4 kg N ha -1 in 1981 to 23.6 kg N ha -1 in 2011 in Canadian farmland.…”

“…In semiarid regions of Canada, nitrate leaching from cropland can still take place and impact water quality depending on the timing of the precipitation events in relationship to nitrogen application and crop uptake [ 39 ]. In Southwestern Ontario, high NO 3 concentrations from N leaching were found in surface waters due to intensive maize cropping with high N inputs and humid climatic conditions [ 33 , 40 ]. A number of modelling studies were carried out to simulate N losses and crop yields in different crop management systems.…”

Solute dynamics and the Ontario nitrogen index: I. Chloride leaching

“…In addition, the utility of "percent solute lost" as an indicator of leaching risk has yet to be determined, along with appropriate risk categories or levels. Further exploration of these concepts occurs in a companion paper (Drury et al 2016), which investigates N dynamics at the same field sites during the same time period. (Table 5).…”

“…The specific objectives of the chloride experiments, reported here, were to (i) compare at each field site the published HSG designation to that obtained using site-measured K sat values and (ii) determine the relationships among measured K sat , HSG category, and observed Cl leaching. The nitrate leaching experiments are reported in Drury et al (2016).…”