versão impressa ISSN 0006-8705
Bragantia vol.11 no.1-3 Campinas mar. 1951
Dosagem dos nitratos do solo pelo método do ácido fenoldissulfônico(1)
F. C. Verdade (2)
Engenheiro agrônomo, Secção de Agrogeologia, Instituto Agronômico de Campinas
This work deals with the nitrates determination bjr the phenoldisulfonic acid method in the soils of São Paulo State. Several modifications were introduced which led to outline an analytical procedure.
The nitrates are extracted by percolation, with a solution of H2SO4 0,01 N which is efficient in obtaining clear filtrates without clay and it is a saving time procedure. The ratio employed to remove soil nitrates is one weight of soil for three volumes of the extractor. The H2SO4 solution was the best extractor found because it dissolves less organic matter from the soil than other methods. Also, with the method described, the operation of removing chlorides is easy and it is possible to use a blank determination.
Losses of nitrates are significant when chlorides are present in concentration as high as 11 e.μg (3.9 p.p.m.). The efficient removal of chlorides by using silver sulfate, can be performed only in acid extracts, if losses of nitrates are to be avoided.
The solution free from chlorides must be neutralized with NaOH 1 N because acid reaction causes loss in nitrates which are liberated as HNO3 (gas). The residual organic matter is destructed with hydrogen peroxide after drying the solution. The hydrogen peroxide always has nitrates and the quantity of them must be determined.
The residual salts from the above treatments are attacked with phenoldisulfonic acid and this solution dilutes to a convenient volume and neutralized with ammonium hidroxide (1 + 1). The color intensity developed in this reaction is read in an AC model Fisher Electrophotometer with B-425 filter calibrated for nitrates. The best readings are between 3-45 or 0,25-16,5 e.μg of NO-3.
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1. A.O.A.C. Em Methods of analysis, pág. 18, 631-32, 6.ª ed., A.O.A.C, Washington 4, D.C., 1945. [ Links ]
2. Berge, T.O. Determination of nitrate with a photoelectric colorimeter. Soil Sci 52 : 185-191. 1941. [ Links ]
3. Cantino, E. C. Elimination of nitrate impurities from 30 per cent hydrogen peroxide. Ind. Eng. Chem., Anal. Edi. 16 : 181-182. 1944. [ Links ]
4. Davis, C. W. Studies on the phenoldisulfonic acid method for determining nitrates in soils. Jour. Ind. Eng. Chem. 9 : 290-295. 1917. [ Links ]
5. Emerson, P. The colorimetric determination of soil in a colored water extract. Soil Sci. 12 : 413-417. 1921. [ Links ]
6. Gericke, W. F. Nitrate determinations in the presence of chlorides. Jour. Ind. Eng. Chem. 9 : 585-586. 1917. [ Links ]
7. Greaves, J.E. e C.T. Hirst. Some factors influencing the quantitative determination of nitric nitrogen in the soil. Soil Sci. 4 : 179-203. 1917. [ Links ]
8. Harper, H. J. The accurate determination of nitrates in soils. Ind. Eng. Chem. 16 : 180-183. 1924. [ Links ]
9. Nemec, V. A. e A. Koppova. Beitrag zur Bestimmung des Nitratstickstoffs im Boden. Ztschr. f. Pfl. Ern. u. Dg., A, 29 : 182-185. 1933. [ Links ]
10. Noyes, H. A. Accurate determination of soil nitrates by phenoldisulfonic acid method. Jour. Ind. Eng. Chem. 11 : 213-218. 1919. [ Links ]
11. Paiva Neto, J. E. Percolação ou agitação, na química dos complexos do solo. Bragantia 2 : 93-99. 1942. [ Links ]
12. Paiva Neto, J. E. e M. Seixas Queiroz. Cloretos (Cl-) nos solos do Estado de S. Paulo, e sua dosagem. Bragantia 6 : 119-142, fig. 1-6. 1946. [ Links ]
13. Paiva Neto, J. E. e outros. Contribuição ao estudo dos métodos analíticos e de extração para a caraterização química dos solos do Estado de São Paulo. Rev. Agr. Piracicaba 21 : 417-458. 1946. [ Links ]
14. Piper, C. S. Em Soil and plant analysis, pág. 206, Interscience Pub., Inc., New York, 1944. [ Links ]
15. Plice, M. J. The determination of nitrates in soils containing soluble organic matter. Soil Sci. 33 : 213-215. 1932. [ Links ]
16. Potter, R. S. e R. S. Snyder. The determination of nitrates in soil. Jour. Ind. Eng. Chem. 7 : 863-864. 1915. [ Links ]
17. Prince, A. L. Determination of total nitrogen, ammonia, nitrates and nitrites in Soil Sci. 59 : 47-52. 1945. [ Links ]
18. Roller, E. M. e N. McKraig, Jr. Some critical studies of the phenoldisulfonic acid method for the determination of nitrates. Soil Sci. 47 : 397-407. 1939. [ Links ]
19. Sachs, W. H. Effect of cultivation on moisture and nitrate content of field soil. Univ. Ark. Agric. Exp. Sta. Bull. 205, pág. 5, 1926. [ Links ]
20. Syme, W. A. The colorimetric determination of nitrates in soil solutions containing organic matter. Jour. Ind. Eng. Chem. 1 : 188-189. 1909. [ Links ]
21. Whiting, A. L., T. E. Richmond e W. R. Schoonover. The determination of nitrates in soil. Jour. Ind. Eng. Chem. 12 : 982-984. 1920. [ Links ]
(1) Trabalho apresentado na Segunda Reunião Brasileira da Ciência de Solo, realizada em Campinas, s. Paulo, de 11 a 26 de julho de 1949 e adaptado para "Bragantia"
(2) O autor agradece aos colegas da Secção de Agrogeologia e, particularmente, ao Eng. Agr. J. E. de Paiva Neto, as sugestões recebidas.