ENVIRONMENT

Emission of methane (CH4) from Italian irrigated ricefields

H. Schutz, Fraunhofer-Institute for Atmospheric Environmental Research (IAER); A. Holzapfel-Pschorn, Max-Planck-Institute for Chemistry, Saarstr. 23, D-6500 Mainz, F.R. Germany; H. Rennenberg and W. Seiler, Fraunhofer-IAER, Kreuzeckbahnstr. 19, D-8100 Garmisch-Partenkirchen, F.R. Germany.

Methane is produced by anoxic degradation of organic matter, primarily in aquatic soil and sediment systems. Flooded ricefields occupy about 1.5 million km2 of the world's total arable land, and are projected to be a dominant source of atmospheric methane.

First field measurements in California, Spain, and Italy indicated that reliable data on the importance of ricefields as a source of atmospheric methane can only be obtained by continuous measurements. We have developed a continuous CH4 sampling and analyzing system (Fig. 1).

Air samples from 16 gas-collecting boxes are taken by means of pumps and flushed through a tubing system to a gas chromatograph for CH4 analysis. The system is run by a programmed microcomputer that also stores the CH4 concentration data reported by the integrator.

CH4 emission rates are calculated from the increases across time in the CH4 mixing ratios inside the closed boxes, as determined 8 times/d on each field plot. This results in a high resolution of the CH4 flux.

We used this system in single-cropped, irrigated ricefields of the Italian Rice Research Institute near Vercelli, Italy. Soil is sandy loam with 2.5% organic C and 0.15% total N. The pH varies between 6.5 and 7.5. The field was wet seeded with pregerminated seeds of a japonica rice variety, for a plant density of 200/m2....