USE OF PHOSPHORUS IN DIFFERENT FORMS 291 



any one of the seven states, Ohio, Maryland, Pennsylvania, 

 Rhode Island, Maine, Massachusetts, or Illinois. 



There are three essential points to be kept in mind concerning 

 the use of raw rock phosphate: 



First, all rock is not phosphate rock, and the farmer should 

 purchase only guaranteed material, and he should know how much 

 phosphorus is contained in the ground rock he applies to the land, 

 if necessary by taking 100 teaspoonfuls from 100 different parts 

 of the car load (including different depths), thoroughly mixing, 

 and sending half a pound of this to a reliable commercial chemist 

 for analysis. 



Second, the rock should be very finely ground, and it should be 

 purchased upon a guarantee that at least 90 per cent of it will pass 

 through a sieve with 100 meshes to the linear inch (10,000 meshes 

 to the square inch) , which is no finer than is required for slag phos- 

 phate. 



Third, raw phosphate should not be expected to give marked 

 benefits except when used in connection with adequate supplies 

 of decaying organic matter. It has practically no value as a top 

 dressing, but must' be plowed under and thoroughly incorporated 

 with the soil where the roots feed. Of course, it will supply only 

 the element phosphorus, and will not take the place of any other 

 deficient element, nor act as a soil stimulant to liberate other plant 

 food from the soil, although it sometimes contains small amounts 

 of carbonate, and then has some tendency to correct soil acidity, 

 but in this it is insignificant compared to the effect of ground 

 limestone. 



The following interesting discussion concerning the use of raw 

 rock phosphate, from the viewpoint of the fertilizer manufacturer, 

 was published in pamphlet form and widely disseminated in 1908, 

 by the National Fertilizer Association. It was also published in 

 full in the American Fertilizer, August, 1908, and in part in Ar- 

 mour's Farmer's Almanac for 1909. It is reproduced in complete 

 form in the following pages, because it deserves to be read by every 

 careful student of soil fertility. Its cautions against the use of 

 raw phosphate as a source of immediately available plant food are 

 commended. It also serves to emphasize the fact stated in the 

 introduction, that, " if the independent farmer is to adopt and 



