DISCUSSION OF RESULTS OF DETERMINATIONS. 



19 



specific physical or chemical factors most influential in the promoting 

 of the formation of nitrates in a given soil type. An attempt was 

 made to correlate the variations in and the amounts of the nitrates 

 found during the season with some of the factors known to influence 

 their formation. As some of the most important ones from a 

 chemical or bacteriological standpoint could not be taken up at the 

 time the attempt at correlation had to be confined to a consideration 

 of some of the physical factors. As, however, the soil of the different 

 plats was similar and probably as nearly uniform as it is possible to 

 obtain soil in different plats, and, furthermore, as the past history of 

 the plats was exactly the same up to the time of beginning the work, 

 it is not likely that there were any fundamental chemical or bacteri- 

 ological differences in the plats at the time of planting. The wheat 

 and corn plats were adjacent and were separated from the fallow plat 

 by only 6 rods, and certainly no differences were apparent. Continu- 

 ous air-temperature records were kept by means of a thermograph, 



Fig. 5.— Diagram showing the average parts per million of water-soluble nitrates in dry soil in the fallow 

 plat to a depth of 2 feet; also soil-moisture curve and precipitation curve. 



but no evident relation could be obtained between the variations in 

 amounts of nitrates and in temperature, whether the mean maximum, 

 mean minimum, or general mean temperature was considered. 



Figure 5 shows the curve of average amounts of nitrates to a depth 

 of 2 feet in the fallow plat, the average soil-moisture curve to the 

 same depth, and the precipitation curve. It is evident that neither 

 the soil-moisture curve nor the precipitation curve shows any close 

 agreement with the nitrate curve. The moisture curve is nearly 

 straight, varying only from 24 to 29 per cent during the whole season. 

 The other two curves parallel from June 19 to the end of the season, 

 but as the formation of nitrates had already taken place and as the 

 amounts thereafter remained constant, it is likely that this agreement 

 is only incidental. It might be mentioned, incidentally, that the 



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