no FUNDAMENTALS OF FRUIT PRODUCTION 



absorbed in the form of nitrate. However, nitrites and salts of ammonia 

 can be utilized to a limited extent, different plants showing considerable 

 variations in this respect. Organic nitrogen also may be a substitute for 

 nitrate, though inorganic nitrogen compounds are used in preference. 

 It has been shown that such nitrogenous soil constituents as nucleic 

 acid, hypoxanthine, xanthine, guanine, creatinine, creatine, histidine, 

 arginine and choline serve as sources of nitrogen when nitrates are absent, 

 but not to any great extent when large amounts of nitrate are pres- 

 gjj^ 163, 169. Moreover, the absorption of nitrate by plants grown in 

 culture is always reduced when creatine or creatinine is present, though 

 the total nitrogen intake remains fairly constant. These organic nitrogen 

 compounds have no effect on potash or phosphorus absorption. 



Bacteria are of great importance in making organic nitrogen com- 

 pounds in the soil more available to the plant and incidentally in destroy- 

 ing toxic substances. Putrefying bacteria, for example, convert the 

 nitrogen of organic compounds to ammonia and nitrogen gas. 



Hart and Tottingham*^ have shown that "soluble phosphates increase 

 enormously the number of soil organisms and the rate of ammonification and 

 destruction of organic matter, while the sulphates activate but slightly in these 

 directions. The processes mentioned are admitted to be of great importance 

 to the plant's nutrition and environment, involving, as they must, not only a 

 more rapid formation of readily soluble compounds of nitrogen and a possible 

 destruction of harmful organic materials, but a greater saturation of the soil 

 moisture with carbon dioxide, resulting in increased solution of mineral materials 

 necessary for rapid growth." Work at the Utah Experiment Station^^ indicates 

 that sulphates have a particularly stimulating effect on soil bacteria under certain 

 conditions. 



Nitrification. — The ammonia produced by bacterial action is in its turn 

 converted to nitrites and these nitrites to nitrates by nitrifying bacteria, 

 each of these changes being carried out by distinct organisms. These 

 organisms require, for the process of nitrification, good aeration, involving 

 both oxygen and carbon dioxide, a certain water supply, the presence of 

 calcium or magnesium compounds, a medium temperature and freedom 

 from an excess of soluble organic compounds or from free ammonia. It 

 is evident that conditions favoring the action of nitrifying organisms will 

 tend to increase the supply of available nitrogen. 



Aided by Liming.— It has been found that applications of lime in many 

 cases increase nitrification. Table 11 presents the results of one such 

 experiment with orchard soils in New Hampshire. Obviously in this 

 instance liming benefited the soil in at least this one direction and it is 

 possible that at the same time it exerted no harmful influence. However, 

 data are presented later to show that it may have a very harmful effect 

 through rendering iron unavailable. Consequently a single fertilizer 

 application may produce at the same time both beneficial and harmful 



