Agriculture, Ecosystems and Environment 83 2001 191–199
Effect of a late season urea fertilization on methane emission from a rice field in Italy
Jianguo Dan, Martin Krüger, Peter Frenzel, Ralf Conrad
∗
Max-Planck-Institut für Terrestrische Mikrobiologie, Karl-von-Frisch-Str., 35043 Marburg, Germany Received 7 March 2000; received in revised form 29 June 2000; accepted 25 August 2000
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 d
13
CH
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. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: CH
4
production; CH
4
oxidation; Paddy field; Ammonium; Methane; Rice; Northern Italy
1. Introduction
Flooded rice fields are one of the major sources of CH
4
to the atmosphere Conrad, 1997; Minami and Neue, 1994; Neue, 1997; Wassmann et al., 1993.
Application of nitrogen fertilizers, among which NH
4 +
-based fertilizers are most common, is nec- essary for rice production. Consequently, effects of
NH
4 +
-based fertilizers on CH
4
emission greatly at-
∗
Corresponding author. Tel.: +49-6421-178801; fax: +49-6421-178809.
E-mail address: conradmailer.uni-marburg.de R. Conrad.
tract the attention of scientists. However, the results from numerous studies have so far been inconsis-
tent, ranging from stimulation Banik et al., 1996; Cicerone and Shetter, 1981; Lindau, 1994; Lindau
and Bollich, 1993; Lindau et al., 1991; Singh et al., 1999 to inhibition Bronson et al., 1997; Bodelier
et al., 2000a,b; Schütz et al., 1989. The effects of NH
4 +
-based fertilizers depend on type and amount of the fertilizer, as well as on mode and time of appli-
cation Cai et al., 1995; Neue and Sass, 1994; Schütz et al., 1989. These studies have also suggested that
the effects of NH
4 +
fertilizers on CH
4
emission can largely be attributed to effects on CH
4
production and
0167-880901 – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 0 0 0 0 2 6 5 - 6
192 J. Dan et al. Agriculture, Ecosystems and Environment 83 2001 191–199
CH
4
oxidation. Whereas urea at normal application rates had little direct influence on CH
4
production Yang and Chang, 1998, CH
4
production may in- directly be increased through improving the growth
of rice plants, since CH
4
produced during the late stage of rice mainly came from root exudates and
root slay Watanabe et al., 1999; Dannenberg and Conrad, 1999; Schütz et al., 1989. Indeed, a higher
CH
4
production potential was shown in rooted than in bulk soil Bodelier et al., 2000b.
Besides CH
4
production nitrogen fertilization may also affect CH
4
oxidation. Methane oxidation requires O
2
and therefore occurs only in the oxic surface layer of the submerged rice soil Conrad and Rothfuss,
1991 and in the vicinity of the rice roots which leak O
2
into the surrounding soil Frenzel et al., 1992; Gilbert and Frenzel, 1998. The effects of NH
4 +
on CH
4
oxidation are variable, from negative to positive. Generally, NH
4 +
has been reported as an inhibitor of CH
4
oxidation Conrad and Rothfuss, 1991; Dun- field and Knowles, 1995; van der Nat et al., 1997,
due to two major mechanisms, i.e., competitive in- hibition and noncompetitive inhibition Bedard and
Knowles, 1989; Gulledge and Schimel, 1998; King and Schnell, 1994; Kravchenko, 1999; Schnell and
King, 1994. In some cases, NH
4 +
reportedly acted as a stimulator of CH
4
oxidation in rice soil Bender and Conrad, 1995; Bodelier et al., 2000a,b, as well
in upland soils Kruse and Iversen, 1995; Goldman et al., 1995; Prieme et al., 1997. When soil suffered
from N limitation, addition of NH
4 +
stimulated the activities of CH
4
-oxidizing bacteria Bodelier et al., 2000a.
Urea, a widely used NH
4 +
-based fertilizer, sup- pressed CH
4
emission over the rice growing season when it was deep-applied Schütz et al., 1989, while
it increased the CH
4
emission when it was broadcasted Lindau et al., 1991; Schütz et al., 1989. Recently,
however, an interesting phenomenon was observed: if planted pots were fertilized with urea, CH
4
emission decreased immediately due to a stimulation of CH
4
oxidation, and this effect was maintained for 1 week Krüger and Frenzel, unpublished. The present study
aimed to confirm, whether application of urea in the field had a similar effect on CH
4
emission. In particu- lar, it is of interest to see whether or not the fertilizer
stimulated the CH
4
oxidation process in the rice rhi- zosphere. Therefore, the effect of fertilization during
the late season was investigated when rice plants were fully grown.
2. Materials and methods
