See more from this Session: Management Strategies to Improve Nutrient Use Efficiency: II
Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
Repeated early season flushing of rice fields greatly affects C and N mineralization, which can result in losses of N and increased greenhouse gas emissions. Therefore, it is important to understand the role of repeated soil drying and rewetting and N fertilization on C and N turnover. This study examined the effects of dry-wet cycling and application of urea on N transformations, dissolved organic matter dynamics, and emissions of CO2. Topsoil (Ap) and subsoil (A) from two different sites in Southeast Texas was divided into two parts, one of which was amended with urea per annual N recommendations for rice (165 kg N ha-1 and 180 kg N ha-1), and another remained unfertilized, resulting in 8 treatments. The soil was incubated in laboratory over 3 consecutive drying and wetting cycles. The concentrations of NH4-N decreased in the fertilized and unfertilized soil at the end of the first drying cycle. The levels of NO3-N increased in all treatments during the same period. Short-term decrease in organic-N and a spike in CO2 emissions during the first drying cycle was likely a result of increase in mineralization and nitrification following initial wetting. The concentrations of total-N in the fertilized treatments were higher in the beginning of the study, but became similar to unfertilized treatments after the first drying cycle. This indicated that the loss of applied N likely occurred during drying and rewetting via ammonia volatilization and N2O emissions. Our results suggest most of applied N is likely to be lost in the initial wetting, and increased greenhouse gas emissions are likely during that period.