June is ,1925 Effect of Crops onYields of Succeeding Crops in Rotation 1099 
basic rotation of a hoed crop with a 
small-grain and a leguminous soiling 
crop, not as applied simply to a particu¬ 
lar representative of each group to 
make up a single rotation, but applied 
under comparable conditions to each of 
three hoed crops, three small grains 
and four legumes, with addition of a 
grass mixture as a nonleguminous 
soiling crop. Thus each of the three 
hoed crops is grown in rotation with 
each of the three small grains and each 
of the five soiling crops, or in 15 com¬ 
plete rotations. The hoed crops also 
are grown in continuous culture and 
alternating among themselves, and in 
rotation with the small grains without 
use of soiling crops. 
Viewed from a somewhat different 
angle, this plan embraces a systematic 
test of the effects of each crop on 
succeeding crops, except that the effects 
of the small grains inter se are not 
included. The basic rotation under 
study somewhat resembles that stated 
by De Candolle to have been in use in 
Norfolk, England, a century ago, con¬ 
sisting of a root crop, a winter cereal, 
and clover. In the tests in which 
soiling crops are not included, a com¬ 
parison of four different fertilizer 
treatments has been made; while, with 
the soiling crops included, a calcium 
phosphate and sulphate of potash have 
been applied uniformly to all plots. 
PRELIMINARY STUDIES 
SOIL SURVEY OF THE EXPERIMENTAL 
PLOTS 
or greensand “marl,” and shells. In a hluil ex¬ 
posure along the north edge of the farm and in a 
road cut near the entrance to the fair grounds the 
greensand content is so high that the whole under¬ 
lying strata has a greenish color. This material is 
ture containing a few gravel and 
which in places are cemented 
together into a loosely consolidated mass. During 
rains the greensand is washed out from the road 
cut, covering the roadbed with a green layer. 
This region is known as the Atlantic Coastal 
Plain. The soil-forming materials of the region 
were transported by water from the older, higher 
country of the Piedmont and Appalachian regions 
to the north. They necessarily have undergone 
changes since washed from their original place oi 
occurrence by processes of abrasion, solution, and 
decay. They are high in content of quartz parti¬ 
cles and, as above stated, contain glauconite, a 
mineral not generally present in the soil of the great 
Coastal Plain region. 
The soils of the experiment plots have been in¬ 
cluded in the Collington series, which typically has 
a brown or yellowish-brown surface with a yellow¬ 
ish-brown, yellow, or greenish-yellow subsoil. The 
lower subsoil is usually more friable and contains a 
higher percentage of coarse-grained sand than the 
upper portion of the subsoil. The amount of the 
greensand material varies considerably. In places 
there is so little that the soil would have been 
mapped as the Sassafras if such areas bad been of 
sufficient size and importance. There is, neverthe¬ 
less. some greensand in all of the soil. The range of 
content is from a percentage so low as scarcely to 
impart a greenish cast to a percentage high enough 
to give a very decided greenish color. The deep- 
green material of the exposures referred to repre¬ 
sents the parent material, that is, the material from 
which the overlying soils have been formed through 
weathering and decay of the greensand beds. There 
is in these soils, of course, much material not de¬ 
rived from greensand, but rather from the quartzal 
and other particles associated with the greensand 
bed. On the slopes outcroppings of gravel are some¬ 
times present. 
Three soil types and five type phases • are present 
on the farm. The texture of the soil and subsoil, 
that is, the relative content of gravel, sands, silt, 
and day, defines the soil-type variations in the 
depth of the surface layers of sand or sandy loam, 
and slight variations in the character of the subsoil 
The effects of crops on others that 
follow undoubtedly depend largely on 
soil conditions, and, moreover, for such 
a large number of plots as are here in¬ 
volved it is not to be expected that 
uniformity of soil can be had. It is 
desirable, therefore, to have as full 
information as practicable concerning 
the characteristics of the soils used in 
the tests. Accordingly, at our request, 
the Bureau of Soils made a survey 3 of 
all the plots, the results of which are 
shown in the soil map and the follow¬ 
ing report by S. W. Phillips: 
The farm is located about one-fourth mile south 
of Upper Marlboro, Md, on a series of flat to un¬ 
dulating terracelike or bench areas rising above the 
Western Branch of the Patuxent River. The slopes 
between the higher and lower flats or benches are 
rather abrupt. The drainage is excellent,, owing 
largely to the porous nature of the subsoil and the 
underlying substrata. The materials from which 
the soils have been derived are of marine origin. 
They contain considerable glauconitic* * material 
The Collington fine sandy loam ( No. 1 ).—This is 
the most extensive soil on the farm. It is a brown 
fine sandy loam to loamy fine sand in the surface 
portion, this passing at about 7 to 10 inches into 
the subsurface layer of yellowish-brown or brown¬ 
ish-yellow fine sandy loam or loamy fine sand. The 
subsoil, beginning at about 16 to 22 inches, consists 
of yellowish-brown to a reddish-yellow sandy clay 
or silty clay loam. In places the greensand content 
is so high that the subsoil has a greenish-brown or 
dark green color. The greensand is present typi¬ 
cally principally in the subsoil, but there may be 
small amounts in the surface soil as well. Below a 
depth of about 30 inches the content of coarse¬ 
grained material is higher and the subsoil accord¬ 
ingly is more porous and open. On the lower bench, 
near the tobacco barn, the surface runs higher than 
the average in content of medium sand, approach¬ 
ing here the texture of a sandy loam. The surface 
soil of Fields I, III, and V of the highest bench con¬ 
tains a little more fine sand and silt than the aver¬ 
age of the Collington fine sandy loam. A few 
patches here of unimportant size are as heavy as a 
very fine sandy loam. The content of greensand is 
higher in the nitrogen and potash plots of the lower 
bench than in the fields of the higher level. This 
may be due or partly due to a transportation by 
rain water of greensand from the outcropping de¬ 
posit on the slope ot the lower level. In parts of 
Plots IVb, IVc, and IVd the amount of greensand 
3 Survey made by Samuel W. Phillips, under direction of Hugh H. Bennett, inspector, southern 
division, Soil Survey Investigations, Curtis F. Marbut, in charge, Bureau of Soils. 
* Glauconite is a hydrous silicate of potassium and iron. 
* A phase is a minor soil variation of local importance. 
