Influence of constant and fluctuating water contents on nitrous oxide emissions from soils under varying crop rotations.

Guo, X.-B., Drury, C.F., Yang, X.M., and Zhang, R. (2010). "Influence of constant and fluctuating water contents on nitrous oxide emissions from soils under varying crop rotations.", Soil Science Society of America Journal, 74(6), pp. 2077-2085. doi : 10.2136/sssaj2010.0064  Access to full text

Abstract

Soil water contents and cropping history influence soil organic matter decomposition, N cycling, and NO3 - losses. However, soil water content fluctuates within and between seasons, which adds complexity to these biochemical processes. The impacts of constant soil water contents (30, 45, 60, 75, and 90% water-filled pore space, WFPS), wet-dry (WD) cycles (90-30% WFPS), and crop rotation (monoculture corn [Zea mays L.], a 2-yr corn-soybean [Glycine max (L.) Merr.] rotation, or a 3-yr corn-soybean-winter wheat [Triticum aestivum L.] rotation) on N2O emissions, inorganic N, and denitrification enzyme activity (DEA) were investigated using repacked soil cores incubated for 50 d. The 30% WFPS treatment resulted in a net accumulation of inorganic N after 50 d. In the constant-WFPS treatments, increasing water content increased DEA, reduced soil inorganic N, and enhanced N2O emissions. When water contents fluctuated in five WD cycles, there was a considerable decrease in NO3 - concentrations, high DEA activity, but low N2O emissions, which were similar to the emissions for the 30% WFPS treatment. Hence, fluctuating soil water content provided a soil environment that may have stimulated N2O reduction to N2 or other microbial processes such as NO3 - immobilization. At the wettest WFPS (90% WFPS), N2O emissions were greater under monoculture corn than the 3-yr rotation, which is consistent with the larger decreases in inorganic N and higher DEA levels. Nitrous oxide emissions accounted for between 7.5 and 27.4% of NO3 - loss when soils were incubated at 90% WFPS but only 3.86 to 5.12% with the WD cycles. Nitrous oxide emissions were found to be influenced by soil water content to a greater extent than crop rotation.