The Extent of Soil Drying and Rewetting Affects Nitrous Oxide Emissions, Denitrification, and Nitrogen Mineralization

Soil drying and subsequent rewetting induces N mineralization and denitrification, but the effects of the "extent" or "degree" of drying and rewetting remains poorly understood. The impacts of different degrees of soil drying (drying to 45, 30, 20, or 10% water-filled pore space, WFPS) and subsequent rewetting (rewetting to 75 or 90% WFPS) on N2O emissions, denitrification, and net N mineralization were investigated. The highest N2O emissions (201 mu g N2O-N kg(-1)) occurred when the soils were dried to 10% WFPS followed by rewetting to 90% WFPS, whereas the lowest emissions (4.72 mu g N2O-N kg(-1)) occurred when the soil was dried to 45% WFPS followed by rewetting to 75% WFPS. When soil was rewetted from 10 to 90% WFPS, cumulative N2O emissions over 120 h were 7.4 times greater than when the soil was rewetted from 10 to 75% WFPS. The proportion of N2O evolved [N2O/(N2O+N-2)] generally increased as the soil dried. Soil rewetting to 75% WFPS generally produced greater N2O/(N2O+N-2) ratios than rewetting to 90% WFPS. Net N mineralization rates in soils rewetted to 75% WFPS significantly increased from 0.78 mg N kg(-1) d(-1) for the soils dried to 45% WFPS to 1.69 mg N kg(-1) d(-1) for the soils dried to 10% WFPS. More extensive soil drying and more extensive rewetting stimulated N2O emissions and total denitrification losses, whereas net N mineralization rates were stimulated only by more extensive drying. Management practices which reduce extreme fluctuations in soil water content may consequently reduce N2O and total denitrification losses.