308 ILLINOIS STATE ACADEMY OF SCIENCE 



SOME ASPECTS OF PHOSPHORUS BEHAVIOR 



IN SOILS 



M. I. Wolkoff, University of Illinois 



Phosphorus, is one of the ten elements necessary for 

 the growth and development of plant tissue. Phosphorus, 

 also, is one of .the three or four of these ten elements that 

 may be lacking in soil for the optimum plant growth. 

 In fact, it is one of the first ones that is usually deficient 

 in the soils of humid regions. The question of phos- 

 phorus and its replenishment in the soil, therefore, be- 

 comes one of paramount importance in agricultural prac- 

 tice. 



There are two main sources of phosphorus that are 

 used by farmers in replenishing the soil, in order to com- 

 pensate for the loss of phosphorus removed by farm 

 crops: (1) farm manures, and (2) commercial phosphatic 

 fertilizers. The phosphatic fertilizers, in their turn, 

 could be subdivided into two main groups, namely: (1) 

 rock phosphate, and (2) acid phosphate. Rock phos- 

 phates are the natural phosphatic deposits quarried and 

 ground into a very fine powder, 80 to 95 per cent of 

 which usually passing through a 100-mesh sieve. Acid 

 phosphate is the product obtained after natural phos- 

 phate is treated with a weak solution of sulfuric acid. 

 Natural phosphate is but very slightly soluble in water, 

 while acid phosphate, freshly prepared, is easily soluble 

 in water. The subdivision, therefore, could be made on 

 the basis of soluble and insoluble phosphatic fertilizers. 

 Other minor sources of phosphorus for use as fertilizers 

 would fall into either of these two main groups. 



According to the American Fertilizer Handbook for 

 1920, there were produced and sold in the United States 

 in 1918, in round figures, 2,500,000 metric tons of rock 

 phosphate, estimated as being worth over $8,000,000. At 

 the same time 4,500,000 tons of acid phosphate were 

 manufactured, being worth over $76,000,000. Nearly all 

 of this vast amount of phosphatic fertilizers was sold on 

 a domestic market and used by American farmers as 

 fertilizer. 



