Measuring and modeling the effects of drainage water management on soil greenhouse gas fluxes from corn and soybean fields
Authors:
Controlled tile drainage can boost crop yields and improve water quality, but it also has the potential to
increase GHG emissions. This study compared in-situ chamber-based measures of soil CH4, N2O, and CO2
fluxes for silt loam soil under corn and soybean cropping with conventional tile drainage (UTD) and
controlled tile drainage (CTD). A semi-empirical model (NEMIS-NOE) was also used to predict soil N2O
fluxes from soils using observed soil data. Observed N2O and CH4 fluxes between UTD and CTD fields
during the farming season were not significantly different at 0.05 level. Soils were primarily a sink for
CH4 but in some cases a source (sources were associated exclusively with CTD). The average N2O fluxes
measured ranged between 0.003 and 0.028 kg N ha1 day1. There were some significantly higher
(p 0.05) CO2 fluxes associated with CTD relative to UTD during some years of study. Correlation analyses
indicated that the shallower the water table, the greater the CO2 fluxes. Higher corn plant C for
CTD tended to offset estimated higher CTD CO2 C losses via soil respiration by w100e300 kg C ha1.
There were good fits between observed and predicted (NEMISeNOE) N2O fluxes for corn (R2 ¼ 0.70) and
soybean (R2 ¼ 0.53). Predicted N2O fluxes were higher for CTD for approximately 70% of the paired-field
study periods suggesting that soil physical factors, such as water-filled pore space, imposed by CTD have
potentially strong impacts on net N fluxes. Model predictions of daily cumulative N2O fluxes for the
agronomically-active study period for corn-CTD and corn-UTD, as a percentage of total N fertilizer
applied, were 3.1% and 2.6%, respectively. For predicted N2O fluxes on basis of yield units, indices were
0.0005 and 0.0004 (kg N kg1 crop grain yield) for CTD and UTD corn fields, respectively, and 0.0011 and
0.0005 for CTD and UTD soybean fields, respectively.