124 EXPERIMENT STATION RECORD. [Vol. 41 



Variability in soils and its significance to past and future soil investiga- 

 tions. — II, Variations in nitrogen and carbon in field soils and their relation 

 to the accuracy of field trials, D. D. Waynick and L. T. Sharp (Univ. Cal. Pubs. 

 Agr. Sci., ^ {1919), No. 5, pp. 120-139, pi. 1). — In a further contribution to the 

 subject (E. S. K., 39, p. 815) the authors present data showing the amount of 

 variation found in total nitrogen and total carbon in silty clay loam soil at 

 Davis and in blow sand at Oakley (Cal.). The total area sampled at each 

 point was a little more than 1.3 acres, the fields being selected for their ap- 

 parent uniformity. Altogether 100 soil samples were taken from each area, 80 

 samples being distributed uniformly at 30-ft. intervals over the entire area, 40 

 samples at 1.5-ft. intervals in 5 different parts of the field, and 12 samples taken 

 within an area of approximately :^ acre in the center of the field. Statistical 

 methods have been applied to the interpretation of the data secured, and the 

 limits of accuracy of the method employed in the nitrogen determinations are 

 discussed at some length. The results obtained may be summarized as follows : 



The extreme range for nitrogen in the Davis soil was from 0.077 to 0.124 per 

 cent, and in the Oakley soil from 0.022 to 0.063 per cent, while for carbon the 

 determinations varied from 0.903 to 1.383 per cent in the Davis soil, and from 

 0.252 to 0.947 per cent in the Oakley soil, indicating that results secured with 

 one or a few samples would probably be unreliable. A study of the relation of 

 soil samples taken from small areas and at short distances apart to those from 

 a larger area and to the whole number of samples taken is held to indicte that 

 " it is unwise to attempt to apply the statistical constants calculated for one 

 area to other areas even though in themselves apparently uniform, since the 

 respective variabilities may be very different." When the variations in the 

 area to be sampled are known, the making of a composite sample is deemed to 

 be fully justified. The relation of variations in a small area to differences be- 

 tween soil types is discussed, and the conclusion reached that only after very 

 careful sampling can such differences be determined with certainty. The ad- 

 vantages of estimating the number of soil samples necessary to secure any 

 given degree of accuracy are indicated. 



[Report of] soil investigations (North Dakota Sta. Rpt. 1917, pp. 15, 16). — 

 Extraction with ammonium sulphate solution and with plain distilled water 

 of both the surface and subsurface 6 in. of limed and unlimed soil grown to 

 wheat continuously for about 40 years, and of a virgin sod resulted in the 

 removal of varying amounts of soluble materials from the differently cropped 

 soils by means of the ammonium sulphate solution. A greater amount of solu- 

 ble calcium was removed from the virgin soil than from the wheat soil, while 

 the amount of soluble magnesium was practically the same for both soils by 

 extraction with ammonium sulphate but greater by aqueous extraction from the 

 wheat soil. There appeared to be little, if any, difference between the two soils 

 in the amount of soluble iron and aluminum. 



With the addition of lime to the.se soils an increase in soluble calcium and 

 a decrea.se in soluble iron and aluminum was obsei-ved. The amount of soluble 

 magnesium increased slightly in all cases, but the proportion of this ingredient 

 to soluble calcium was much less in all the limed samples. Aqueous extracts 

 of the limed soils showed a much smaller content of soluble calcium and mag- 

 nesium for the virgin soil than for the wheat soil. 



These results are held to indicate that continuous cropping to wheat has 

 caused a loss of calcium carbonate in this soil, and that the proportion of 

 soluble magnesium to soluble calcium has undergone a change. No definite re- 

 sults have thus far been secured regarding soluble iron and aluniinuni. 



Azofication, J. E. Grea\'es (Soil Sci., G (1918), No. S, pp. 163-217, figs. 2).— 

 This paper, a contribution from the Utah Experiment Station, comprises a 



