SOILS FERTILIZERS. 1025 



number of soils, both in tlic Held and in tlie plant house, are described. The 

 results in general indicate with reasonable certainty "that acid soils need phos- 

 phates, and it will be possible, by a careful test of a soil with litmus paper, to 

 tell if it needs, or will need in the immediate future, a phosphate fertilizer." 



The nitrogen content of soils as affected by methods of farn^ing, A. R. 

 Whitson, C. W. Stoddart, and A. F. McLeod (Wificoiisin 8ta. Rpt. 1906, pp. 

 160-110). — Studies of cropped and virgin soils similar to those reported by 

 Snyder of the Minnesota Station and Ladd of the North Dakota Station are 

 reported. 



Analyses were made of samples of soil from a large number of fields, the 

 liistories of which are fairly well known, and of samples of virgin soil sur- 

 rounding and adjacent to them. Summing up the results it is shown "that, in 

 (I out of 121 cases, the difference in amount of nitrogen in the virgin and cropped 

 soil is not enough to account for the crops which have been -removed." It is 

 suggested that this condition is a result of fixation of nitrogen by soil bacteria. 



" On the average, the determinations show that the loss by leaching and deni- 

 trification amounts to only 22.3 per cent of the amount of nitrogen removed by 

 crops. The evidence seems to indicate that in clay loam soils of moderate fer- 

 tility more than four-fifths of the nitrogen lost is removed by crops. 



" It is probably true that in soils of a higher degree of fertility, and especially 

 where large amounts of fertilizers are used on land growing late cultivated 

 crops, there is a larger loss of nitrogen by leaching and denitrification than is 

 noted in the above cases. Nevertheless, the entire loss of nitrogen from these 

 fields is, on the average, 37.1 i)er cent of their original content, as determined 

 by this method. This indicates clearly the limited store of nitrogen in such 

 soils and the importance of maintaining it by the growth of clover, or other 

 legumes, and manure." 



Denitrification in cultivated soils, G. Ampola and S. de Gkazia (Staz. Sper. 

 Af/r. Itah, 39 {1906), 'So. 6-7, pp. 593-609; Gas. Chim. Hal, 36 (1906), II, No. 

 .J-6. pp. 893-905; ofis. in Chem. Zcntbl., 1907, I, So. 7, pp. 655, 656). — In continua- 

 tion of previous experiments by Ampola (E. S. R., 17, p. 17) the authors here 

 report a series of comparisons on volcanic soils of calcium and sodium nitrates 

 and farm maniu'es as regards the changes which their nitrogen undergoes in 

 the soil and their efficiency when used singly or in combinaticm on different 

 crops. 



It was found that the nitric nitrogen of calcium nitrate is more readily 

 assimilated by plants than that of sodium nitrate, which is ascribed to the fact 

 that calcium nitrate is the ultimate product of nitrification in the soil, and nitro- 

 gen in this form offers greater resistance to denitrifying organisms than that 

 of sodium nitrate. This fact, first pointed out by Ampola in 1901, has been 

 confirmed by recent experiments by Bellenoux (E. S. R., 17, p. 449). 



It was also found that denitrification was less rapid in the case of well 

 rotted manure than of fresh nninure. Denitrification was apparently greater 

 and the resultant yield of crops less in case of manure containing litter than 

 in case of manure not containing such material. The application of straw to 

 the soil in all cases caused a decrease in yield, and even when sodium nitrate 

 was used with the straw the yield was but very slightly increased. The inju- 

 rious effect of the straw both alone and in connection with sodium nitrate and 

 manure is attributed in part to the increased aeration of the soil brought 

 about by its use, which is believed to promote denitrification. The decrease in 

 yield is attributed more especially to denitrification becaus(» the soils experi- 

 mented with were such as are ordinarily benefited by aeration and are rendered 

 more productive by the common practice of plowing under stubble or sod. It is 



2849— No. 11—07 m 3 



