Regionalisation of nitrate leaching on pasture land in Southern Manitoba
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Date
2017
Authors
Simratpal, Singh
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Abstract
Nitrogen is a key agricultural input which is considered to be crucial for crop growth, development, and yield. However, an excess application of anthropogenic nitrate in the form of fertilizers may result in the nitrate contamination of groundwater. A critical time in continental climates in Canada having long and cold winters is nitrate leaching during soil thawing since fast recharge fluxes may occur during that time. The objective of this research was to estimate leaching fluxes of nitrate upon the application of liquid hog manure on a pasture land in Southern Manitoba using physically based modeling and to further regionalise the point estimates of nitrate leaching fluxes at the field scale. Data for this research were taken from the Ph.D. study by Coppi (2012). During that study, the field site located in La Broquerie, Manitoba was divided into 6 types of plots namely - control-hayed, control-grazed, full-hayed, full-grazed, split-hayed, and split-grazed treatment plots. The control, full and split treatments plots represented no application of manure, one-time application in a year with full rate and two-times application in a year with half rates each time respectively. Haying and grazing were two types of forage harvesting treatments carried out on in the study site. One-dimensional physically based modeling was applied using HYDRUS-1D to determine continuous recharge and nutrient leaching estimates from these data. The regionalisation of simulated leaching estimates was done using Cokriging which is a geostatistical interpolation approach. The difference in simulated and observed nitrate concentrations in groundwater was expressed in terms of RMSE between 0.023 and 5.12 mg NO3-N L-1, NSE between 0.66 and 0.96 and the ME between -1.03 mg NO3-N L-1 and 1.05 mg NO3-N L-1. The areas which posed a risk to nitrate contamination of groundwater were the bare earth areas (BEA). The observed and simulated results showed that the groundwater nitrate concentrations in BEAs of both control-grazed and full-grazed plots were consistently higher than 10 mg NO3-N L-1. Overall, the cumulative nitrate leaching fluxes for control-hayed, full-hayed and control-grazed plots were below 2 kg NO3-N ha-1 for both years. However, for full-grazed plots, the cumulative nitrate leaching flux was about 11 kg NO3-N ha-1 and 6 kg NO3-N ha-1 for 2008 and 2009 respectively. The cumulative leaching fluxes in BEAs were about a hundred times larger than those in grassed areas. Overall, HYDRUS-1D can be considered as a useful tool in quantifying nitrate leaching estimates for pasture fields subjected to continental climates, and Cokriging can be considered as a reliable method for a study site where cross-correlations between variables are important to consider for carrying out interpolation.
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Keywords
Nitrate leaching, HYDRUS-1D, Physically based modeling, Liquid hog manure, ArcGIS, Cokriging