Effect of a late season urea fertilization on methane emission from a rice field in Italy

Abstract

The application of NH 4 +-based fertilizers is a common practice in rice production. The immediate effect of a late season urea application on the processes involved in CH 4 emission from a rice field was investigated on sandy loam located in the valley of River Po at Vercelli, northern Italy, and planted with rice ( Oryza sativa, type japonica, variety Koral). Urea, applied at a rate of 50 kg N ha −1 on the 75th day after flooding, significantly stimulated both CH 4 production and CH 4 oxidation. During the following 9 days, the rates of CH 4 production and CH 4 oxidation in the 0–3 cm soil layer increased by 24–52 and 18–41%, respectively, of the fertilized plot compared to the unfertilized control plot. Methane oxidation on roots was also stimulated by urea, indicated by shorter lag times. Porewater concentrations of CH 4 in the 0–6 cm soil layer increased with time and soil depth, but were not affected by fertilization with urea. Urea application also exhibited little impact on CH 4 emission. During the 7 days following fertilization, urea only slightly reduced the CH 4 flux. Ammonium originating from urea hydrolysis was completely depleted from the porewater within 3 days, mainly due to plant uptake. Fertilizer application did also not affect the contribution of CH 4 oxidation to the net flux of CH 4, determined by measuring δ 13CH 4 and by inhibition of CH 4 oxidation. The absence of any effect of urea on net CH 4 emission in this study was presumably caused by the rapid depletion of urea, the counterbalance between the increase of CH 4 production and the increase of CH 4 oxidation after fertilization, and methanogenesis in deeper soil layers.