26 MANURING OF POTATOES. 

valued at 50s. per ton instead of £3, the profits on the arti-_ 
ficials would have varied from 12s. to 30s. per acre. 

At four of the stations where the experiments were carried 
out, the potatoes foliowed several years’ lea, either directly 
(in two cases) or after a single year’s interval of a cereal 
crop; at the other two plots they were taken after a cereal 
crop grown in ordinary rotation. It was noticed that the artin- 
c:als when used alone did best at the four stations upon which 
the potatoes were taken after several years’ lea, and that at 
the remaining two the plots getting dung took the lead. 
There was, Dr. Somerville says, considerable evidence that 
the season was exceptionally favourable to the action of 
artificial manures for rather, perhaps, unfavourable to dung), 
but, allowing for this, there can be little doubt that a good 
general mixture of artificials can be relied upon to produce a 
first-rate crop of potatoes after lea. In the present instance, 
moreover, the artificial dressings did very well after stubble 
also, but the more restricted accumulation of organic matter 
(humus) in the soil after stubble makes the use of dung much 
more important than is the case where the land has been 
broken up out of lea. , 
Professor Campbell's experiments were carried out at the 
Garforth Farm of the Yorkshire College, Leeds, and on three 
other farms, there being in all five series of plots. In com- 
paring the results the average of the five series is taken; the 
potatoes are valued at Sos. per ton (large and small together). 
The whole cost of the artificials has been charged against the 
crop; but in the case of the dung, which is not all exhausted 
in the first year, it has been assumed that it will be about 
half exhausted, and its value has accordingly been put at 
2s. 6d.per ton. The main question studied was the deter- 
mination of the kinds and quantities of artificials which may 
be applied with greatest profit along with farmyard manure. 
Professor Campbell states that the ‘standard ’ dressing of 
artificials (13 cwt. sulphate of ammonia, 3 cwts. superphos- 
phate, 2 cwts. sulphate of potash, costing altogether 
#2 11s. 4d.) applied with 10 tons dung per acre yielded about 
1 ton of potatoes more than the dung by itself; but a double 
dressing of dung alone yielded better results, in the dry 
