Resumo

REUSSI CALVO, Nahuel I; ECHEVERRIA, Hernán E  e  SAINZ ROZAS, Hernán. Comparison between two plant nitrogen and sulphur determination methods: impact on wheat sulphur diagnostics. Cienc. suelo [online]. 2008, vol.26, n.2, pp.161-167. ISSN 1850-2067.

The nitrogen and sulphur ratio (N:S) in plants is often used as a sulphur diagnostics tool in wheat. This ratio requires two different analyses results for its calculation, and thus involves two sources of analytical error. The objective of this work was to compare the accuracy and reliability of the Dumas dry combustion method for N and S determination in plant, compared to traditional methods of wet digestion, and its use as a sulphur diagnostics tool in wheat. The N and S determination was carried out in wheat plant samples from four experiments carried out in the 2006 growing season in the southwestern Buenos Aires province. A highly significant correlation was obtained between both methods (r = 0.99 and r = 0.74 for N and S, respectively). The quantity of N recuperated by the Dumas method was not significantly different to the Kjeldahl method, however, the reliability of the former was higher (low variability coefficient). The method of turbidimetry with wet digestion underestimated (20%) the sulphur concentration compared to the Dumas method. Moreover, the sulphur percent recovered from standard samples was 83 % and 96 % for the turbidimetry and Dumas methods, respectively. The underestimation of plant sulphur concentration by the turbidimetry method resulted in a low percentage of samples correctly diagnosed (25, 18.7 and 50% for Z22, Z24 and Z31, respectively). However, the percent of samples correctly diagnosed was high by the Dumas method (94, 94 and 100% for Z22, Z24 and Z31, respectively). The results of this work indicate that the reliability of the N:S ratio is limited by the S analysis accuracy. On the other hand, the N recovery for both methods was similar.

Palavras-chave : Methods of plant analysis; Nitrogen and sulphur.

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