Some Observations on manuring witli Bone-dust. 



109 



Average of three parallel pots. 



If we now assume the total yield of the pots B to be =100, we obtain 

 the following' ratio : 



A (MgCOs) 



B (MgSOi) 



C (CaCOs4-MgC03) 



D (CaC0;^ + MgC03) 



E (CaS04-^-MgC03) 



F (K.jCOo + MgCOg) 



96 



ICO 



85 

 64 



n6 

 33 



From the observations and this yield, it may be inferred : 



1. Alagnesit acts like limestone, depressing the availability of bone dust 

 (compare A, C and D with B^^ 



2. The ratio CaO : Mg=2 : i (D) depressed the harvest more than the 

 ratio CaO : Mg= i : i (A) which is in full accordance with results 

 obtained also in other cases with cereals. 



1). Recently Koch and Grober (Fiihlings Landw. Zeitg. 1906, p. 225) inferred from their 

 experiments that this depressing effect is also due to the neutralization of the acids produced by 

 bacteria in the soil. But the conditions in the soil are often entirely different from these in flasks. 

 These authors applied solutions of 2-5 % dextrose to bone dust in the absence and in the presence of 

 calcium carbonate, aud of course observed that in the absence of calcium carbonate the phosphate 

 was dissolved considerably by the bacterial action. But in the soil, suitable carbohydiates are 

 generally absent, and therefore acid can not be produced. On the contrary, the soil-bacteria produce 

 ammonium carbonate by the rottening process of the organic matter of the bone dust, and in this 

 case the solubility of the tertiary phosphates will certainly be very much smaller than in the former 

 caie, i.e. in the presence of glucose. 



