VoL. LXXVII. 
NEW YORK, JULY C, 1918. 
No. 44S9. 
Does Alfalfa Enrich 
the Soil? 
I have before me an ar¬ 
ticle in Tife R. N.-Y., page 
12.’55. issue of Nov. -b. 1917, 
v.hioh deals with the mat¬ 
ter of leguminous crops and 
the accumulation of nitro¬ 
gen. In this connection I 
take pleasure in calling your 
attention to the paper of 
Prof. C. O. Swanson in the 
•Tournal of the American So¬ 
ciety of Agronomy. Vol. 
No. 7, October. i‘.>17. and. 
fearing that you m.ay not 
have this publication at 
hand. I inclose his summary 
of this article : 
1. “Kansas has a number 
of Alfalfa fields which have 
been continuously in this 
crop for 20 to 90 years or 
more. The older fields are 
found in the Central and 
■Western part of the State. 
Near these fields generally 
are fields which are in na¬ 
tive sod used as pasture or 
as hay land, and fields which 
have been used continuously 
for grain growing for .90 to 
40 years or moi-e. By 
samnling these fields in close 
proximity, data are .secured 
fi-om which the increase or 
decrease in the nitrogen con- 
t'Mit of the soil in .Mf.alfa 
can be calculated. 
2. “By assuming th.at the 
fields now in Alfalfa had 
the same nitrogen content 
originally as the fiehl now in 
native sod. and that the av¬ 
erage annual rate of loss 
before the Alfalfa was seed¬ 
ed was the same as that of 
the fields used for continu¬ 
ous grain growing, the nitro¬ 
gen content at the time the 
Alfalfa was seeded can be 
calculated. By comparison 
with the results of the three 
fields at the present time, 
calculation can be made of 
the increase or decrease of 
nitrogen content due to the 
growing of Alfalfa. 
.9. “In no fields in Alfalfa 
is the nitro.gen content equal 
to that in native sod. ex¬ 
cept a few in the semi- 
arid portion of the 8tate 
where it was greater. In 
most cases in the fVntr.al 
and Eastern parts of tin' 
State the nitrogen content 
of the Alfalfa field is greater 
than that of the field used 
for continuous grain gi’ow- 
ing. By accounting for that 
lost before the Alfalfa was 
seeded, and comparing with 
the amount present in the 
soil now. it is found that on 
the w'hole the growing of 
Alfalfa has not added to 
the amount present in the 
soil, except in a few fields 
in the semi-arid portion of 
the State. All that the 
Alfalfa has done has been 
to prevent further loss. or. 
in other words, to main¬ 
tain an equilibrium.” 
A Rotation for Alfalfa Best 
Y OU will notice that 
Prof. Swanson’s arti¬ 
cle (Journal of the -Viner- 
ican Society of Agronoin.v, 
October, 1917) is entitled 
“Effect of Prolonged Orow- 
in.g of Alfalfa,’’ etc., and 
the article shows that he 
dealt with fields that luni 
h'cn in Alfalfa for 10 tc 
•9'’, years. J’he opinion has 
been .generall.v hehl. as I 
iinih'rstand it. that if the 
legumes find an abundant 
supply of nitrogen in the 
.soil they do not e.vert them¬ 
selves to obtain it from 
tilt' atinosidiere. If this 
Opinion is correct, we 
would exiiect that after tlie 
Alfalfa hail accuinulatt'I 
a sullicient store of nitro¬ 
gen to meet the ileniands 
of its annual growth, there 
would he no fnrtht'r in¬ 
crease in it; nitrogen stor¬ 
age. 
It would scein that the 
addilion to the soil of 
nitrogen b,v legumes would 
he found cliietly in the 
ronts and their notluies, 
not in an.v direct (h'posit 
of nitrogen in the soil it¬ 
self. When the roots iiave 
attaineil their maximum 
devt'Iopment there would 
thei'cfore he hut little fur¬ 
ther increase in the soil 
nitrogen, except that re¬ 
sulting from the annual leaf 
Av.-istage, which is not 
.gri'at under good Iuh- 
handr.v. The Alfalfa roofs, 
like the top, are perennial. 
They do not humify, an I 
thus ht'come permanent res¬ 
ervoirs of nitrogen until the 
])lant dies. For this rea¬ 
son. and hecau.se of the 
groat draft hy .Mfalfa on 
the mineral elements of 
the soil. I have long iloubt- 
ed the wisdom of letting it 
occup.v the land as long as 
has been done in these 
Kansas fields, anil in the 
oxiieriments which we are 
planning for Ohio we ex¬ 
pect to rotate the Alfalf.’ 
as .systematica ll.v as we 
would clover, the only dif¬ 
ference being that the Al¬ 
falfa requires a longer pe¬ 
riod to reach its maximum 
development than clover 
does. 
The article in question 
does not state when the 
samplin.g was done. The 
annual removal of the 
Alfalf.'i hay carries with it 
a much larger quantity 
of nitrogen than that of 
the non-le.guminous crops, 
and hence there might be 
a greater variation in the 
nitrogen level in the soil 
at different .sea.sonal dates 
with Alfalfa than with the 
At the left a single phint of Coasnel- Alfalfa transplanted four gears ago. At the right a plant grains and grasse.s. On 
of tStrri-t elovi-r. Fig. 417 the whole, I do not doubt 
