— 35 ~ 
ject to modification, due to the formation of amides; also a 
small amount of ammonia from the albuminoids. 
« \ 
ELEMENTS OF PLANT FOOD TAKEN FROM THE SOIL. 
The leguminous plants, to which order alfalfa belongs 
store up in their stems a. large amount of nitrogen which 
they are believed to obtain largely from the atmosphere,and 
tor this reason they are considered as nitrogen gatherers 
adding to the soil more nitrogen than they draw from it’ 
provided the plants are not removed, but fall where thev 
?u°'c ?‘! ai i e P 10 '^ ul }der. But, when the hay is taken off 
t le held, the problem is a different one, and whether it adds 
to the nitrogen in the soil or takes from it, depends upon the 
ratio ot the nitrogen in the leaves and stems which fall and 
decay upon the soil to that taken from the soil proper in the 
form of nitric nitrogen. As I know nothing of the value of 
this ratio,lam compelled to content myself with the o- e neral 
results which are well known ; still, under the discussion of 
the roots, we shall see that there are reasons why we are justi- 
tied in doubting whether the store of nitrogen in the soil is 
added to by growing alfalfa; on the contrary, while this 
plant is provided with tubercles—micro-organisms which 
enable it to appropriate atmospheric nitrogen—it is also a 
greedy feeder upon the soil nitrogen. 
The benefits which accrue to soils cropped to alfalfa 
are unquestionably great, but whether they are lasting, or 
call for a quick rotation in order to be maintained, is still to 
be established. The case of the other elements of plant 
food is not involved by any compensation as in the case of 
nitrogen ; but every pound taken away is at the expense of 
the supply in the soil. As our soils have not been under 
crops of any kind very long, and to alfalfa only a short 
time, it is a leasonable assumption that the average mineral 
constituents of the ash correspond very nearly to the re¬ 
quirements of the plant. The quantities given by our 
analyses, repi esenting plants supplied with an abundance 
ot available food, are probably high enough. 
The accompanying table gives the ash constituents 
taken from the soil with every 1,000 pounds of hay. The 
sand, carbon, and carbonic acid are rejected in this table. 
1 here may appear to some to be a discrepancy between 
the table as given on page 31, and the following; the two 
are, however, the same as concerns the following subtances 
contained in the ash: 
