84 CYANAMID — MANUFACTURE, CHEMISTRY AND USEJS 



since prices vary, it is customary to express the yields on 

 the basis of equal applications of nitrogen. 



There is therefore a large number of factors that affect the 

 selection of the most economical fertilizers. The statistical 

 method of merely averaging the yields of a large number of 

 experiments regardless of their character, does not give very 

 much practical information. The errors of experimentation 

 with Cyanamid are usually in one direction, and hence do 

 not offset one another. One of the most common errors is 

 the use of quantities of nitrogen far in excess of what would 

 be applied in practical agriculture, as indicated on page 69. 

 It is shown in Fig. 5 that the relative efficiency of utilization, 

 of the nitrogen in various compounds is not the same at all 

 applications. The relative values at an application of i gram 

 per pot are entirely different from the relative values at 0.5 

 grams, or at lower applications. Moreover, the order of 

 superiority may be different at different applications, as shown 

 on the calcium nitrate curve. At the lower concentrations, 

 such as obtain in practical agriculture, under favorable 

 soil conditions, all of the common nitrogenous mineral 

 fertilizers have about the same efficiency of utilization, 

 in this experiment. Not only is it a mistake to assume that 

 results obtained at one concentration will hold true for other 

 concentrations, but it is, of course, equally wrong to assume 

 that an average of the results at various concentrations will 

 hold true for a particular concentration. The relative effi- 

 ciencies also vary with the nature of the soil and with the 

 crop. Results obtained on sand may not hold on clay, and 

 vice versa. Acid soils may act differently from neutral or 

 alkaline soils. A nitrogenous fertilizer applied alone usually 

 gives entirely different results when mixed with other nitro- 

 genous fertilizers, or with phosphates, acid or basic, or with 

 potash salts. 



A source of error that has probably vitiated many of the 

 reported experiments is the readiness with which unhydrated 

 lime-nitrogen changes in weight, by absorption of moisture 



