Traditional Sources of Nitrogen

Recycling was particularly important in areas with adequate precipitation or in regions where irrigation either removed or at least alleviated the recurrent threat of 

Declines of soil organic matter with crop cultivation. 

The simplest way of recycling crop residues is to burn cereal stubble, crop stalks, or vines in the field, a practice still common in all traditional agricultures. As with the burning of original vegetation by shifting farmers, this combustion of crop residues in harvested fields returns all mineral nutrients to the soil in the remaining ash. 

Crop residues have also provided indispensable feed (sometimes from stubble grazing, mostly as stall-fed roughage) and bedding for domestic animals, especially for ruminants whose nutrition requires a minimum share of roughage in order to maintain normal rumen activity. Cereal straws and a few other residues (cotton waste, banana leaves) are also an excellent substrate for cultivation of white button and straw mushrooms, and in some societies residues have been used for making paper. 

Chinese rice straw dried for feed, fuel, and animal bedding. Photo by V. Smil. 

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The traditional and the still widely used synthesis of ehloro-cyclophosphazenes consists of the reaction of finely ground ammonium chloride (the source of nitrogen) with phosphorus pentachloride (the source of phosphorus) (see Eq. 3.1). This reaction is carried out in a high boiling chlorinated solvent such as symmetrical tetrachloroethane, CI2CHCHCI2 or chlorobenzene. This reaction is quite complex. Ammonium chloride is not soluble in these solvents, while phosphorus pentachloride is. Thus, the overall reaction is heterogeneous in nature. A complex mixture of cyclic and linear products is formed in this reaction. Individual chlorocyclophosphazenes can be separated fi-om each other by various means. 

Many bacteria perform services we find useful and even necessary, although we rarely take note of them. Some bacteria participate in the decomposition of dead plants and animals and so help recycle chemicals that are otherwise locked away from the living world. Some are sources of antibiotics that have revolutionized the treatment of infectious disease in the past fifty years. Others are responsible for nitrogen fixation, converting relatively inert atmospheric nitrogen into biologically useful ammonia—a conversion that is not simple in the chemical laboratory. Still other bacteria are indispensable in the world s kitchens, for without them there would be no cheese or yogurt, nor any of hundreds of other traditional milk products. We could not enjoy pickles or sauerkraut, and... 

The reductive process is the more traditional process for tire pyrolysis. This process excludes all sources of oxygen and relies on the reactor heat alone to decompose the tires. Some processors pressurize the reactor with an inert gas such as nitrogen to prevent air from leaking into the reactor, while some inject hydrogen to react with the sulfur present in the rubber in the tires to form hydrogen sulfide. Hydrogen sulfide can be recovered and sold as a by-product. 

Reactions in proteins and other nitrogenous compounds catalyzed by endogenous enzymes are responsible for desirable and undesirable sensory attributes of foods — color, flavor, and texture — as well as for the development of compounds that are nutritionally beneficial or have detrimental effects on human health. The use of added enzymes or enzyme sources is also an essential part of many traditional methods of food processing. Since the conditions of enzymatic reactions are much milder than those applied in chemical treatments, different added enzymes are being used to an increasing extent to modify the functional properties of food proteins. 

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