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Elevated Atmospheric Carbon Dioxide in Agroecosystems Affects Groundwater Quality
Author(s) -
Torbert H. A.,
Prior S. A.,
Rogers H. H.,
Schlesinger W. H.,
Mullins G. L.,
Runion G. B.
Publication year - 1996
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/jeq1996.00472425002500040011x
Subject(s) - loam , agroecosystem , fertilizer , agronomy , sorghum , nitrate , leaching (pedology) , groundwater , chemistry , environmental science , soil carbon , carbon dioxide , environmental chemistry , soil water , soil science , ecology , biology , agriculture , geology , geotechnical engineering , organic chemistry
Increasing atmospheric carbon dioxide (CO 2 ) concentration has led to concerns about global changes to the environment. One area of global change that has not been addressed is the effect of elevated atmospheric CO 2 on groundwater quality below agroecosystems. Elevated CO 2 concentration alterations of plant growth and C/N ratios may modify C and N cycling in soil and affect nitrate (NO 3 − ) leaching to groundwater. This study was conducted to examine the effects of a legume [soybean [ Glycine max (L.) Merr.]] and a nonlegume [grain sorghum [ Sorghum bicolor (L.) Moench]] CO 2 ‐enriched agroecosystems on NO 3 − movement below the root zone in a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split‐plot design replicated three times with plant species (soybean and grain sorghum) as the main plots and CO 2 concentration (∼360 and ∼720 µL L −1 CO 2 ) as subplots using open‐top field chambers. Fertilizer application was made with 15 N‐depleted NH 4 NO 3 to act as a fertilizer tracer. Soil solution samples were collected weekly at 90‐cm depth for a 2‐yr period and monitored for NO 3 − ‐N concentrations. Isotope analysis of soil solution indicated that the decomposition of organic matter was the primary source of NO 3 − ‐N in soil solution below the root zone through most of the monitoring period. Significant differences were observed for NO 3 − ‐N concentrations between soybean and grain sorghum, with soybean having the higher NO 3 − ‐N concentrations. Elevated CO 2 increased total dry weight, total N content, and C/N ratio of residue returned to soil in both years. Elevated CO 2 significantly decreased NO 3 − ‐N concentrations below the root zone in both soybean and grain sorghum. The results of this study indicate that retention of N in organic pools because of elevated atmospheric CO 2 could reduce the nitrate concentration in groundwater beneath agroecosystems as indicated by NO 3 − movement.