Methane Emissions from Main and Ratoon Rice Crop Under Different Water Management Systems in Louisiana.

Field experiments were conducted in 2013 and 2014 to examine the effect of water management practices on methane (CH₄) and nitrous oxide (N₂O) emissions from Louisiana rice fields. Emissions under four water management treatments were studied and included: Continuous Flooding (CF), Straight Head (SH), Intermittent Flood (IF) and Semi-Aerobic (SA). Gas samples were collected one week prior to flood initiation and continuously weekly following flooding until harvest using static diffusion chambers. A Varian CP 3800 gas chromatograph fitted with flame ionization detector was used for CH4 analysis.

Accumulative CH₄ fluxes for the 2013 main crop were 215, 211, 134, and 134 kg ha-1in SH, CF, IF, and SA water treatments. Total CH₄ flux (including ratoon crop) for the entire season was highest in SH (445 kg ha^-1), followed by CF (428 kg ha^-1), SA (375 kg ha^-1) and IF (258 kg ha^-1). In 2014, methane emissions of the main crop and ratoon crop has similar trend with 2013 but the total emission in 2014 was slightly higher than 2013. In both years, methane emissions for the ratoon crop were significantly higher than the main crop, particularly at about 4 weeks after re-flooding the field. It might be because of the straw leftover after harvesting the main crop, which could be a major carbon source for microbial. Results showed that water management techniques could be used to reduce methane emissions from rice field. However, a significant yield reduction was also observed in Semi-Aerobic water management.