444 
Journal of Agricultural Research 
Vol. V, No. io 
Observations taken on August 21 showed that the cowpeas on the 
plowed plot were only a little heavier than those on the adjacent unplowed 
plot. Blossoms had already begun to appear, and runners measured 
from 1 to 2 feet in length. Some crab-grass had sprung up, but only a 
few other weeds were noticed. The shade devices were in very good 
condition and the soil beneath seemed normal except that it was covered 
with a growth of green algae. This was also true of the soil of the cow- 
pea plots, but to a less marked extent. 
Great care was given to details, such as freeing from weeds, renewing 
the covering of the shade device, etc., throughout the season. Just 
before frost, compactness tests were again made on all plots after remov¬ 
ing the cowpea vines. The vines were cut with a scythe and the strip 
walked on by the operator was eliminated from the test areas. The 
data on soil compactness secured for October 15 are given in Table III. 
TablB III .—Relative compactness (number of drops of mm) of soil on the various plots , 
as measured on October 15, 1912 
Trial No. 
Plot D 
(unplowed; 
clean). 
Plot E 
(unplowed; 
cowpeas). 
Plot B 
(plowed; 
cowpeas). 
Plot G 
(plowed; arti¬ 
ficial shade). : 
Plot H 
| (plowed; 
I clean). 
I.. 
20 
18 
4 
6 
c; 
2.. 
19 
12 
5 
6 
6 
3 .. 
17 
19 
3 
5 
7 
4 . 
18 
II 
3 
6 
6 
5 . 
20 
14 
5 
6 
6 
6. 
24 
17 
3 
6 
5 
7 .. 
20 
14 
4 
6 
5 
8. 
20 
I 5 
3 
5 
S 
9 . 
*9 
17 
3 
5 
7 
ro. 
22 
17 
5 
5 
6 
11. 
16 
IS 
4 
7 
8 
12. 
16 
15 
S 
6 
5 
13 . 
23 
IS 
3 
6 
5 
14. 
19 
3 
4 
7 
6 
15 .. 
19 
18 
5 
7- 
S 
16. 
20 
16 
3 
6 
7 
17. 
21 
16 
4 
6 
7 
18.. 
18 
iS 
5 
6 
8 
l 9 . 
19 
11 
S 
5 
6 
Average. 
19. 4 
IS* 4 : 
! 
5- 9 
6 
The relative compactness as shown in Table III was duplicated, using 
a modification of the method which originated with Wollny 1 —i. e., the 
apparent specific gravity of the soil in each plot was determined. A 
metallic brass tube 7.8 cm. in diameter was driven to a depth of 23.2 
cm. in the soil. The tube was then dug out and the contact below 
broken. Duplicate cores of soil from each plot were thus secured, taken 
to the laboratory, dried, and weighed. The dry weight of the soil divided 
by the volume of the cylinder (1,465 c. c.) is the apparent specific gravity 
1 Wollny, Ewald. Der Einfluss der Pflanzendecke und Beschattung . . . 197 p., 10 pi. Berlin, 1877. 
