Nitrates in soils

Davidson, E.A., Hart, S.C. and Firestone, M.K. 1992 Internal cycling of nitrate in soils ofamature coniferous forest. Ecology 73 1148-1156. 

All positively charged nitrogen species and all organic nitrogen-containing compounds are readily converted to nitrite and then to nitrate in soil. Because of this ready conversion, all are sources of nitrogen for plants. 

Cawse PA.The determination of nitrate in soil solutions by ultraviolet spectroscopy. Analyst 1967 92 311-315. 

Blackmer AM, Bremner JM (1977) Nitrogen isotope discrimination in denitrification of nitrate in soils. Soil Biol Biochem 9 73-77... 

Waughman [14] has described a microdiffusion method for the determination of ammonium and nitrate in soils. Nitrate in the sample solution is reduced to ammonia by titanous sulfate and the ammonia is then released from the solution and diffused and absorbed onto a nylon square impregnated with dilute sulfuric acid. The nylon is then put into a solution which colours... 

Techniques used to determine nitrates in soils include titration [17], spectrophotometry [18-26,29-31], flow injection analysis [20,21], ion selective electrodes [27,28], and ion chromatography [28,31-44],... 

Garcia Gutierrez [19] has described an azo coupling spectrophotometric method for the determination of nitrite and nitrate in soils. Nitrite is determined spectrophotometrically at 550 nm after treatment with sulfuric acid and N-1 -naphlhylclhylcnediamine to form an azo dye. In another portion of the sample, nitrate is reduced to nitrite by passing a pH 9.6 buffered solution through a cadmium reductor and proceeding as above. Soils were boiled with water and calcium carbonate, treated with freshly precipitated aluminium hydroxide and active carbon, and filtered prior to analysis by the above procedure. 

Elton-Bott [22] and Osibanjo and Ajaya [23] determined nitrate in soil by a spectrophotometric method based on 3,4-xylenol. In one of these procedures [28], nitration of the 3,4-xylenol is carried out instantaneously at about 0 °C in 80% sulfuric acid and the nitration product is extracted into toluene, the excess of the reagent remaining in the aqueous layer. The toluene layer is then treated with sodium hydroxide solution to form a coloured product (the sodium salt of the nitrophenol in the aqueous layer), the absorbance of which is measured at 432 nm. Interferences from common anions, including chloride and nitrate, were investigated. 

Goodman [28] described an automated procedure for the determination of nitrate in soils. The apparatus automatically extracts and analyses batches of up to 60 soil samples. Analysis is performed electrochemically by means of an ion-selective electrode and reference electrode. Corning ion-selective electrodes were found to be superior to those produced by Orion in this application. Recoveries of nitrate in this method were between 94 and 95%. The calibration curve was linear down to 2.5 mg/1 nitrate. A plan of the general arrangement is shown in Fig. 6.3. 

Tecator Ltd. (1983) Determination of Nitrate and Ammonia in Soil Samples, Extractable with 2 M Potassium Chloride Application Note AN65/83 (1983) and Determination of Nitrate in Soil Samples, Extractable with 2 M Potassium Chloride using, Flow Injection Analysis, Application Note AN65-31/83, Tecator Ltd., Hoganes, Sweden. 

The Rhizobium occurs in specialized nodules on the roots of the legumes. These are developed when the soildwelling Rhizobium invades a root hair, stimulating the plant to form a nodule. Nodule development is inhibited in acidic soils and if the concentrations of nitrate in soil are large. To protect the nitrogenase enzyme, the interior... 

ISEs designed for polyatomic anions such as N03 and CIO4 make use of strongly hydrophobic cations as ion exchangers. Typical examples of suitable cations are shown in table 9.7. The nitrate electrode responds to other anions, especially perchlorate. It is widely used to test for nitrates in soil samples and agricultural products. 

S. McLeod, Micro-distillation unit for use in continuous flow analyzers. Its construction and use in determination of ammonia and nitrate in soils, Anal. Chim. Acta 256 (1992) 107. 

J. Keay, P.M.A. Menage, Automated determination of ammonium and nitrate in soil extracts by distillation, Analyst 95 (1970) 379. 

Terrazole has also an inhibiting effect on microorganisms active in the nitrification process (i.e., the conversion of ammonium salts to nitrates) in soil.486-"488 However, under field conditions, the inhibition of nitrification is of limited duration pasture yields, for example, are not increased.489 3-Trichloromethyl-l,2,4-thiadiazole-5-amines exhibit the same properties 490... 

Like Terrazole, 3,5-diamino-1,2,4-thiadiazole acts as an effective inhibitor of the oxidation of ammonium salts to nitrates in soil.506... 

E. B. Schalscha, T. Schirado, and I. Vergara, Flow Injection Analysis of Nitrate in Soil Extracts—Evaluation of a Nitrate-Selective Flow Electrode Method. J. Soil Sci. Soc. Amer., 45 (1981) 446. 

Much of our knowledge of availability of fixed ammonium has been bdsed on nitrification tests, since it is well established that any nitrogen that undergoes oxidation to nitrates in soil is available for use by higher plants. This represents the minimum that is available it is likely that some plants can assintilate some of the nitrogen that Nitro-somonas cannot utilize, especially if the plants are removing ions or other substances that interfere with the release of ammonium from the clay lattices. 

In a system with active denitrification, nitrate levels are usually low, thus, measurement of nitrate in soil and water column does not provide a reliable indication of this process. As denitrification is mediated by heterotrophic microorganisms, its rate may be regulated by nitrate concentration (electron acceptor) and available C (electron donor). Significant correlations were observed between denitrification rates and available organic C (mineralizable organic C) (Gale et al., 1993 D Angelo and Reddy, 1999). Similarly, MBC and denitrification enzyme assay (DEA) can also serve as potential indicators of denitrification rates (White and Reddy, 1999). 

Measurements of nitrate in soils and waste waters using the TOAN-DBP electrode and the brucine method agreed closely. All these nitrate ISEs (66,67) are subject to serious interference from iodide, chlorate and perchlorate. This feature can in turn be exploited, e.g., the Corning nitrate exchanger may be readily converted to a viable chlorate-sensing cocktail using an extraction technique as described for the uranyl phosphate sensor (section 3.2.10). 

Waste protein gets changed back to nitrates. In soil, there are bacteria which feed on the protein in dead plants and animals, and in animal manure. They change it back to nitrates, which can be used again by plants. 

Ammonia is produced by the reduction of nitrogen-containing matter (e.g. aminoacids, amines, amides and nitrates) in soil to form ammonia. For example... 

BROADBENT F.E. 1973. Sources and sinks of nitrate in soils. In Proceedings of the first annual trace contaminants conference. 

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