SOIL CONDITIONS AFFECTING PLANT GROWTH 77 



manure were found by Bogdanow to be helpful. 1 Dymond (92) 

 showed that sulphates increased the yield of heavy crop's rich 

 in protein, although they were not needed for cereals or per- 

 manent pastures. A number of recent investigations in the 

 United States by Pitz, 2 H. G. Miller, C. B. Lipman and W. 

 F. Gericke (175^) and others have confirmed and extended 

 these observations : the last-named authors found that sulphate 

 of ammonia was superior to nitrate of soda for barley on 

 certain Californian soils, though it was no better than a mix- 

 ture of nitrate and sulphate of soda. 



Silicon does not seem to be essential in any quantity, but 

 it occurs to so large an extent in some plants that it is not 

 likely to be wholly useless. Wolff and Kreutzhage (315) 

 found that soluble silicates increased the yield of oats in water 

 cultures and also the proportion of grain, behaving, in their 

 opinion, much like phosphates. On some of the phosphate- 

 starved plots at Rothamsted marked crop increases are ob- 

 tained by addition of sodium silicate (Table XXIV.). Hall 

 and Morison (120^) conclude that silicates act by causing an 



TABLE XXIV. EFFECT OF SILICATES ON THE GROWTH OF BARLEY, 1864-1904. 



ROTHAMSTED. 



increased assimilation of phosphoric acid by the plant, the 

 seat of action being in the plant and not in the soil. Bene- 

 ficial results were likewise obtained by Jennings. 8 



i Expl. Stat, Record, 1900, n, 723, and 1903, 15, 565. 



2 Pitz, Journ. Ag. Research, 1916, 5, 771-780; H. G. Miller, Journ. Ag. 

 Research, 1919, 17, 87-102. 



3 Soil Sci., 1919, 7, 201. 



