tion rates and greater immobilization generated by surface residues (Rice and Smith, 1984).

A simple and fast method was developed for the determination of traces of Fe, Mn, Cu, Cr, Ni, Zn and Mo in endive using wavelength-dispersive x-ray fluorescence spectrometry. Plants were grown in different sewage sludge compositions for 60 days in greenhouse conditions. Samples were compacted and analyzed after drying, milling and homogenization. The method was validated using certified standard reference materials. The results were compared with those obtained by atomic absorption spectrometry. Good agreement for all elements was obtained. The detection limits were found to be Fe 1, Mn 3, Cu 2, Cr 5, Ni 1, Zn and Mo 3 µg g −1 . These results permitted the evaluation of the potential use of sewage sludge as an agricultural amendment.

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We report the first measurements of methane emitted by cattle of the Argentinean beef system, one of the largest in the world. Special care was taken to keep the animals under production conditions typical of the Pampa, the main livestock region of the country. Therefore, we applied the SF 6 tracer technique to 20 young Aberdeen Angus steers randomly chosen in a commercial farm, in which paddocks they were left to graze. The liveweight change of the animals, the herbage allowance and quality were followed during the research. The magnitudes varied significantly throughout the experiment (which included two separate periods of time, the first during December 2005 and the second in February-March 2006) and from paddock to paddock. In spite of these differences, the average daily methane emissions per head rarely depart from 170 g/day However, larger variations were observed in the methane yield and, specially, in the methane em itted per weight gained. The work was also useful to analyse some technical features of importance in making the technique suitable for growing steers under the extensive condition prevailing in the Argentinean beef system.

No abstract