9 6 



PHYSIOLOGY OF NUTRITION 



Phosphorite fertilizers had very good effects upon the uncultivated sands 

 (Podsol), but no effect at all upon the black soil. The sands apparently in- 

 creased the solubility of phosphate rock, since summer-rye cannot assimilate 

 phosphoric acid in the form in which it occurs in this fertilizer, and the black 

 soil appears to have had no such effect. 



In sand cultures phosphorite can be made available for the small grains by 

 supplying them with a complementary fertilizer, such as ammonium salts, 

 which are physiologically acid. Since adequate amounts of ammonium salts 

 are usually injurious to plants in water and sand cultures, Prianishnikov 1 re- 

 placed only a part of the requisite sodium nitrate in his sand cultures by an 

 equivalent amount of ammonium sulphate. This gives a medium that tends 



Fig. 60. — Effect of ammonium salts upon the availability of phosphorite for oats in sand 

 cultures. (After Prianishnikov.) See text for explanation. 



to become more acid with increase in its content of the ammonium salt, and so 

 phosphate rock supplied to such cultures might be expected to become soluble 

 and thus available to the plants. This expectation was realized in experiments 

 with oats. The results of such an experiment are given in the table below. The 

 appearance of the first six cultures, in the order followed in the table, is shown in 

 Fig. 60. 



Culture Treatment Weight of Tops 



No. grams 



1 Control, KH2PO4 + NaN0 3 19 ■ 7 



2 Phosphorite + NaN0 3 6.9 



3 Phosphorite + 1 4(NH 4 ) 2 S0 4 + MNaN0 3 22.0 



4 Phosphorite + H(NH 4 ) 8 S04 + 3^NaN0 3 20. 5 



5 Phosphorite + ^(NH 4 ) 2 S0 4 + MNaN0 3 192 



6 Phosphorite + (NH 4 ) 2 S0 4 1.6 



1 Prianishnikov, D. N., Results of vegetation experiments for 1899 and 1900. [Russian.] Bull. Moscow 

 Agric. Inst. 7 (non-official part) : 85-129. 1901. 



