1110 
Journal of Agricultural Research 
Vol. XXX, No. 12 
results even on the soils used in the 
present tests. But no system of active 
cropping seems to give such uniformly 
good results as resting the land, thus 
allowing it to be occupied for a time by 
adventitious vegetation (pi. 3, B). 
a second-year crop. The location of 
these cropping units on the field, as 
well as the cropping system applied to 
them, are readily identified by com¬ 
bining the section and division designa¬ 
tions, as, for example, C 1, A 2. 
FIELD STUDY OF THE COMPARA¬ 
TIVE EFFECTS OF TOBACCO AND 
OTHER CROPS ON THE YIELDS 
OF SUCCEEDING CROPS 
In these tests tobacco has been com¬ 
pared, in all instances, with early 
potatoes and cofrn. Each of these crops 
has been grown (1) in continuous 
culture and in alternation with each of 
the other two; (2) in rotation with each 
of the small grains, wheat, oats, and 
rye; and (3) in rotation with each of 
the small grains and each of two winter 
legumes, two summer legumes, and a 
grass mixture. Except where the soil¬ 
ing crops are used, four different fer¬ 
tilizer treatments have been applied in 
each system of cropping. To carry out 
these tests has required 5 separate 
fields and a total of 261 plots. The 
second feature of the tests was begun 
in 1914, but the entire plan was not 
in full operation till 1916. The results 
to be presented at this time are more 
or less of a preliminary nature and are 
subject to some modification as the 
work progresses. For this reason only 
summarized tabulations of yields will 
be given, leaving for future publica¬ 
tion a more complete presentation of 
the detailed results for each year. 
The general plan in conducting the 
tests has been to plant the three hoed 
crops—tobacco, potatoes, and corn—in 
adjoining, parallel strips of suitable size, 
the total area embraced in the three 
strips being designated as a “field.” 
The three strips embraced in a field 
are called “sections,” designated by 
the letters A, B, and C. In the second 
year three crops, consisting of the same 
three hoed crops or three small grains, 
as the case may be, are planted cross¬ 
wise the original strips or sections and 
the strips occupied by the second-year 
crops, which run at right angles to the 
sections, are called “divisions.” These 
divisions are distinguished by the num¬ 
bers 1, 2, and 3. This of course pro¬ 
vides for each of the first-year crops 
to be followed by each of the second- 
year crops. Thus, each of the three 
sections of the field occupied by a 
first-year crop is crossed by each of 
the divisions occupied by a second- 
year crop, and vice versa. The effect 
is to divide the field into nine “cropping 
units/ each of which embraces a com¬ 
plete 2-year rotation of a first-year and 
FERTILIZER TREATMENTS 
By making the cropping units of 
sufficient size they may be subdivided 
into as many plots as desired for 
fertilizer tests or for adding legumes 
to the rotations, both of which features 
have been made a part of these tests. 
In this way it becomes possible to 
compare crop effects with fertilizer 
effects and, moreover, the plan may be 
made to furnish a comprehensive test 
of the fertilizer needs of the soil. In 
the present tests only four different 
fertilizer treatments have been used, 
involving omission of nitrogen, phos¬ 
phoric acid, and potash, respectively, 
in comparison with a standard rate 
of application of the three elements. 
High-grade dried blood has been used 
as a source of nitrogen because it 
supplies only small percentages Cof 
phosphorus, potassium, magnesium, 
sulphur, or other plant-food elements. 
A chemically precipitated dicalcic 
phosphate has furnished phosphoric 
acid, and high-grade sulphate of potash 
has been used as a source of potash. 
The standard rates of application per 
acre, arbitrarily selected, were 20 
pounds each of nitrogen and potash 
and 40 pounds of available phosphoric 
acid. For convenience in indicating 
the different fertilizer treatments, the 
letters N, P, and K are used to desig¬ 
nate applications of 20 pounds nitrogen, 
40 pounds phosphoric acid, and 20 
pounds potash per acre, respectively. 
The standard rates of application per 
acre with the corresponding symbols, 
therefore, are as follows: 
1 f 20 pounds nitrogen_ 
\40 pounds phosphoric acid . 
9 f20 pounds nitrogen- 
\20 pounds potash- 
o /40 pounds phosphoric acid - 
6m 120 pounds potash.. 
1 20 pounds nitrogen_ 
40 pounds phosphoric acid . 
20 pounds potash. 
N+P 
N+K 
P+K 
N+P+K 
None of the fertilizer materials used 
furnish important quantities of plant 
nutrients other than the three in ques¬ 
tion, except that the sulphate of potash 
supplies approximately 20 pounds per 
acre of sulphur trioxide and the dicalcic 
phosphate supplies about 25 pounds of 
calcium oxide. To avoid any possible 
shortage of calcium in the soil, and to 
at least partially overcome any soil 
acidity, a ton per acre of shell lime- 
