Significant accumulation of nitrate in Chinese semi-humid croplands.
Soil nitrate is important for crop growth, but it can also leach to groundwater causing nitrate contamination, a threat to human health. Here, we report a significant accumulation of soil nitrate in Chinese semi-humid croplands based upon more than 7000 samples from 141 sites collected from 1994 to 2015. In the 0-4 meters depth of soil, total nitrate accumulation reaches 453 ± 39, 749 ± 75, 1191 ± 89, 1269 ± 114, 2155 ± 330 kg N ha(-1) on average in wheat, maize, open-field vegetables (OFV), solar plastic-roofed greenhouse vegetables (GHV) and orchard fields, respectively. Surprisingly, there is also a comparable amount of nitrate accumulated in the vadose-zone deeper than 4 meters. Over-use of N fertilizer (and/or manure) and a declining groundwater table are the major causes for this huge nitrate reservoir in the vadose-zone of semi-humid croplands, where the nitrate cannot be denitrified due to the presence of oxygen and lack of carbon sources. Future climatic change with more extreme rainfall events would increase the risk of accumulated nitrate moving downwards and threatening groundwater nitrate contamination.
College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
Junyu
J
Zhou
Department of land Management, Zhejiang University, Hangzhou 310058, PR China.|Policy Simulation Laboratory, Zhejiang University, Hangzhou 310058, China.
Baojing
B
Gu
Cary Institute of Ecosystem Studies, Millbrook, NY 12545, USA.
William H
WH
Schlesinger
College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
Xiaotang
X
Ju
D002681:China; D018556:Crops, Agricultural / Q000254:growth & development*; D004784:Environmental Monitoring; D060587:Groundwater; D009566:Nitrates / Q000032:analysis*; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis
D009566:Nitrates; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical