446 MANURING OF POTATOES. 
The important principle that manures, when given in 
quantities in excess of a certain limit, produce a constantly 
diminishing effect, was also exemplified in the use of arti- 
ficial manures in the Durham experiments of 1899. 
Experiments 1n Co. Durham in 1899—Average of Six Farms. 

| 


ncrease Ov 
Plot. Manures Applied per Acre. re Increase over 
| Unmanured Crop. 
ae = 
7 
Tons cwis. 97s. 
IO | 12 tons farmyard manure - > - - - - | 2 16 ig 
6 as A ‘5 with 124 cwt. mixed artificials 3 IQVs)3 
8 rs < a with 64 cwt. a a Vs 14S 


In this instance 64 cwts. of mixed artificials added to 12 tons 
of farmyard manure gave a return of 174 cwts. potatoes, but 
when another 6} cwts. of the same artificials were added the 
further increase of the crop amounted to only 5! cwt., or less 
than one third of that produced by the first application. 
A somewhat similar result is recorded in the Glasgow 
reports of 1899. In the experiments of that year the addi- 
tion of 6 cwts. mixed artificials to 20 tons farmyard manure 
gave an average increase of crop of 7? cwts. potatoes; but 
when the same artificials were added to 10 tons of farmyard 
manure they gave an increase of 18 cwts., or nearly three 
times as much. 
All these results, found on ascrop which responds readily 
to the action of manures, and which gives a more profitable 
return for them than most crops grown on the farm, indicate 
very clearly the importance of determining for each crop not 
only the most suitable kind of manure, but also the quantity 
in which it ought to be employed. It is obvious that in all 
cases there is a point beyond which the application of 
manure ceases to be profitable, though the limit is one that 
' may vary with every season as well as with every crop. But 
even an approximate determination of the maximum profit 
limit up to which manures should be applied, but beyond 
which the application should cease, seems to be one of the 
objects that ought to be kept steadily in view in the arrange- 
ment of further field experiments. 
