New YorkK AGRICULTURAL EXPBPRIMENT STATION. 355 
1. Very much better crops of lettuce may be forced by using 
stable manure for enriching the soil than by using only commer- 
cial fertilizers of the kinds tested. 
2. When the soil is used for the first time for forcing a crop 
of lettuce, an abundance of manure may be used with good re- 
sults but where the use of manure is continued with the same 
soil year after year the optimum amount may be expected to 
decline towards the 5 per ct. rate. It is evident that the amount 
which it is economical to use varies with the character of the 
soil and of the manure and also with the relation of the prices 
for a fancy product to those paid for ordinary lettuce. For 
these reasons no definite recommendations can be made as to 
the amount of manure which it is profitable to use in forcing 
lettuce. 
3. In forcing lettuce it is not good economy to make repeated 
applications of manure in excessive quantities to the same soil. 
Not only is manure thus wasted but the yield may be actually 
decreased. 
WHY DO THE SMALLER AMOUNTS OF MANURE GIVE RESULTS BETTER 
THAN THOSE OBTAINED WHERE THE MANURE IS APPLIED IN 
EXCESSIVE QUANTITIES? 
With the smaller amounts of manure applied to soils which 
had received an abundance of nitrogen, phosphoric acid and 
potash in commercial fertilizers the yield was much greater than 
it was on similarly treated soils without any manure, but where 
the manure was used in excessive quantities the yield, as has 
been shown above, dropped below that obtained with less 
manure. Why is this so? What factors of fertility does the 
manure introduce into the soil aside from the plant-food which 
it contains? The data bearing upon this question which have 
been obtained in carrying out the experiments under discussion 
have not all been presented in this account of the work. Other 
experiments which may throw light on this subject are now in 
progress. The discussion of this question will therefore be de- 
ferred till further data have been secured. 
