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Nitrate Leaching in Californian Rice Fields: A Field‐ and Regional‐Scale Assessment
Author(s) -
Liang X. Q.,
Harter T.,
Porta L.,
Kessel C.,
Linquist B. A.
Publication year - 2014
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2013.10.0402
Subject(s) - leaching (pedology) , groundwater , fertilizer , nitrate , soil water , environmental science , paddy field , dns root zone , hydrology (agriculture) , aquifer , lessivage , soil horizon , agronomy , soil science , chemistry , geology , geotechnical engineering , organic chemistry , biology
Irrigated croplands can be a major source of nitrate‐N (NO 3 –N) in groundwater due to leaching. In California, where high NO 3 –N levels have been found in some areas of the Central Valley aquifer, the contribution from rice systems has not been determined. Nitrate leaching from rice systems was evaluated from soil cores (0–2 m), from the fate of 15 N fertilizer in replicated microplots, and from about 145 regional groundwater wells. Soil NO 3 –N concentrations were ≤3.3 mg kg −1 (usually <1 mg kg −1 ) below the root zone (below 33 cm depth). In pore‐water samples, NO 3 –N was observed only below the root zone during the first 2 wk after the onset of flooding in either the growing season or the winter fallow period and was always ≤8.4 mg L –1 . Fertilizer 15 N accounted for 0 to 11.8% of NO 3 –N in pore‐water samples below the root zone. One year after application, based on an analysis of soil core samples, on average 2.5% of fertilizer N was recovered as 15 N below the root zone (33–100 cm), possibly due to leaching in permeable soils or via preferential flow through cracks in heavy clay soils. Based on a regional assessment, groundwater samples from wells that are located in proximity to rice fields all had measured median NO 2 –N and NO 3 –N levels below 1 mg L −1 . These results indicate that NO 3 –N leaching from the majority of California rice systems poses little risk to groundwater under current crop management practices.