10 CONTROL SERIES No. 109 



Explanation of Tables of Analyses 



Guarantee. The plant food guarantee or the grade of each fertilizer is made 

 a part of the trade name under the heading "Name of Manufacturer and Brand," 

 and is expressed as nitrogren, available phosphoric acid, and water soluble potash 

 and in that order. 



Mixtures Showing a Commercial Shortage of $1 or More per Ton. A 



study of the following table will show that apparently either improper mixing or 

 segregation after mixing is still playing a major role in causing serious deficiencies. 

 The deficiencies found in the high analysis grades showing plant food content 

 greatly disproportionate to the guaranteed analysis are probably due to the effect 

 of segregation. Some of these mixtures are composed of particles varying greatly 

 in shape, size, and specific gravity. Under these conditions, even with very thor- 

 ough mixing to obtain a uniform mixture and careful subsequent handling of the 

 fertilizer, segregation probably cannot be entirely eliminated. Once segregation 

 has occurred it is almost impossible to obtain a sample which will yield an analysis 

 closely resembling the guaranteed analysis. 



The adequacy of existing sampling methods in obtaining representative samples 

 of fertilizer mixtures possessing pronounced segregative tendencies has been ques- 

 tioned, and the suggestion made that sampling methods be revised and adapted 

 to cope with the qualities peculiar to such mixtures. This would seem to be put- 

 ting the cart before the horse. 



Past experience has established fairly definitely that present methods of samp- 

 ling employed by the fertilizer control agencies of most states are fully adequate 

 for securing representative samples of reasonably well mixed fertilizers. There is 

 a serious question whether it is possible or even desirable for any sampling method 

 to do more. It is very difficult to determine what constitutes a representative 

 sample of a badly segregated mixture. 



The manufacturer's concern over the condition of his product should not cease 

 even when he has added all the necessary ingredients in the proper proportions 

 and his own chemists have found the fertilizer as it is in the curing bins or as it 

 comes from the bagging mill comfortably above guarantee in all elements. There 

 is an obligation on his part to market a well mixed fertilizer of uniform composi- 

 tion containing ingredients of such particle size that it will withstand all the rough 

 handling to which fertilizer is usually subjected and will reach the farmer and 

 eventually the soil with every portion of the fertilizer still containing the plant 

 food elements in substantially the same proportion as guaranteed on the tag. 



Some manufacturers are prone to pass over this problem too lightly, implying 

 that there is no practical difference as far as crop yield is concerned whether one 

 plant food element is 2 or 3 per cent under guarantee and another 2 or 3 per cent 

 over guarantee, or whether all plant food elements are as guaranteed. However, 

 if with all the care exercised by the inspectors in obtaining official samples it is 

 not possible in some instances to secure samples which will show a deficiency of 

 less than 2 per cent in one element and an overrun of less than 2 per cent in another, 

 there is ample justification for assuming that the fertilizer represented by such an 

 analysis will reach the soil, after it has undergone considerably more handling 

 and has been agitated in a drill attachment or fertilizer sower, in an even more 

 unbalanced condition. That a fertilizer possessing segregative qualities is still 

 further segregated during its application to the soil has been shown in work done 

 by Mehring, A. L., White, L. M., Ross, W. H. and Adams, J. E., U. S. Dept. of 

 Agriculture Tech. Bull. 485 (1935). Also W. II. Ross, of the Fertilizer Research 

 Division, Bureau of Plant Industry (Ross et al., Jour. A.O.A.C. Vol. 24, No. 2, 

 499, 1941) states: "for many years numerous field tests have been made to de- 



