Nitrite, reaction with organic matter

A nitrification inhibitor that is fully effective would be expected to (1) increase efficiency in the use of nitrogen fertilizers, especially on coarse-textured soils where rainfall is high, or extensive irrigation is practiced (2) make more feasible the practice of fall applications of ammonia (3) make less critical the time of nitrogen fertilizer applications and the need for split applications and (4) reduce nitrogen losses that may occur via nitrite decomposition or reaction with organic matter. Whether the benefits to be expected are sufficient to more than offset the costs of the chemical, and the additional steps involved in its use, is a practical matter that must be determined by the user for his particular soil and cropping system. 

The experiments cited above are in general agreement with the conclusions of Clark and Beard (1960), Clark et al. (1960), and Broadbent and Clark (1965) that nitrite reactions with soil organic matter play an important role in the loss of nitrogen gas and nitrous oxide. Some of the results of Tyler and Broadbent (1960) can probably be explained in a like manner although the absolute proof is lacking. These workers did not determine how much, if any, of the nitrite was fixed by the organic matter. 

Equations 17.14 and 17.15) induced by the same classes of compounds already seen for particulate matter [46]. Transformation of organic compounds dissolved in water droplets can also take place because of reaction with the powerful oxidizing agent OH. This species can be produced on photolysis of H202 (see Equation 17.6, [12, 27]), nitrate (Reaction 17.16, which is also valid for aqueous solutions), and nitrite [47]. 

The significance of the nitrite—soil organic matter reaction in connection with the loss of gaseous nitrogen in the forms of N2 and N O is considered in Chapter 13. 

These data in Fig. 12.2 and 12.3 leave no doubt that chemical nitrification of nitrites to nitrates occurs readily in 1% potassium phosphate solutions that are more acid than about pH 4.0. In soils it has been shown (Stevenson and Swaby, 1964 Fuhr and Bremner, 1964a Stevenson et al., 1970) that a portion of any nitrous acid formed can react with soil organic matter, especially at the lower pH values, but a considerable portion of it decomposes to liberate NO. Quantitative data on the extent of these reactions under a wide variety of soil conditions have not yet been reported. Mortland and Wolcott (1965) and Mortland (1965) have shown that NO can penetrate the interlamellar surfaces of montmorillonite and in the presence of air it is oxidized at a rate dependent upon its diffusion to the edge of the particle. All of the nitric oxide was oxidized in 24 h or less. These data leave no doubt that nitrite undergoes nitrification in soils very much as in phosphate buffer solutions, except possibly to a lesser extent since a portion of it is fixed... 

Major limiting factors controlling anaerobic ammonium oxidation reaction are the availability of nitrite and the competition for electron acceptors by heterotrophs. Soils and sediments with high organic matter content can create higher demand for electron acceptors (nitrite and nitrate). Under these conditions, anammox may not be able to keep up with denitrification when electron donor availability is very high. It is likely under available carbon-limiting conditions that some autotrophs... 

Cu11 complexes undergo photoreduction to the Cu1 species and may be the photocatalyst in photo-oxidation cycles of organic environmental matter, quite similar to the Fem species [20, 81] (see Figure 9.11). Dissolved copper compounds are important to transformation reactions, because they react with hydroperoxyl (H02) and superoxide (02 ) radicals much faster than other species present in the solution. Oxidation of Cu1 and Fe11 by H202 is a source of the OH radicals in oceans comparable with nitrite photolysis, whereas photochemistry of Cu11 chlorocom-plexes provides Cl radicals [81] ... 

---