The Duration of the Action of Manures. 
1 25 
3. The Phosphatic Fertilisers. 
The following Table IV. shows on the same lines as before 
the results yielded by the three phosphatic fertilisers under 
trial : — 
Table IY. — Yield from phosphatic fertilisers over a period 
of four years. 
Yield.— Total produce (unmanured plot = 100) 
Year of 
application 
1 year old 
residue 
2 year old 
residue 
3 year old 
residue 
Mean of 9 
Mean of 8 
Mean of 7 
Mean of 6 
Superphosphate . 
116-2 
109-6 
113-8 ' 
107-8 
Bone Meal .... 
114-6 
112-4 
109-1 
105-6 
Basic Slag .... 
114-5 
110-5 
104-8 
112-0 
These results are significant in two directions, one that the 
phosphatic manures persist in the soil and the residues exert an 
effect that is roughly proportional to the amount of phosphate 
unused, secondly, that superphosphate is as lasting a manure as 
either bone meal or basic slag. Neither conclusion can be said 
to be wholly unexpected or unjustified ; it has already been 
shown that at Rothamsted the phosphoric acid contained in the 
superphosphate applied from year to year still persists in the 
surface layer in a state of combination soluble in dilute citric 
acid, and therefore readily available for the use of the crop. If 
then the soluble phosphoric acid of superphosphate is thus 
definitely arrested and kept in a valuable form there is no 
reason to expect any greater deterioration in the phosphates of 
bone meal or basic slag, which remain effective in so far as 
they have not been taken out by the crop. This conclusion is 
perhaps to be limited to a soil like that of Rothamsted, 
reasonably well furnished with carbonate of lime, so that the 
compounds formed in the soil by the soluble phosphoric acid 
will be mainly those containing lime. Returning to the 
original object of these experiments it is clear that the com- 
pensation to be paid for a dressing of phosphatic manure must 
be spread over a longer period than that given for most kinds 
of nitrogenous fertilisers. 
Phosphatic manures are usually applied in considerable 
quantity ; 1 cwt. of superphosphate will contain from 14 to 
20 lb. of phosphoric acid, 1 cwt. of bone meal about 25 lb., and 
1 cwt. of basic slag about 20 lb. of phosphoric acid, yet most 
crops do not remove more than 20 to 30 lb. per acre of phosphoric 
acid (mangolds up to 50 lb. per acre or more). Hence with 
the ordinary dressings we may assume that at least one half of 
the original value of the manure remains in the soil after the first 
