118 Journal of Agricultural Research voi. xxi, No . } 
cotton plots in 1912 and 30 plots devoted to this crop each year since 
1913. Of this number, 4 have been in cotton continuously, 20 have 
been in cotton each alternate year, 4 have been in cotton every third 
year, and 2 have been in cotton every fourth year. 
The table also gives the average yield of all cotton plots in the rotations 
in pounds of seed cotton per acre, the total annual precipitation as 
recorded at the experiment farm, and the precipitation occurring during 
the crop season each year from April 1 to October 31. 
Table J..—Average percentage of cotton plants killed by rootrot in the rotation experiments 
at San Antonio, Tex., the average yield of these plots in pounds of seed cotton per acre, 
the total annual precipitation, and the seasonal precipitation, April to October, for the 
years 1912 to 1919 
1912 
1913 
1914 
1915 
1916 
1917 
1918 
1919 
Average percentage of plants 
killed by rootrot . 
O. A 
I. 7 
o n 
*7 T 
12. 7 
26. 0 
Average yield in pounds of 
seed cotton per acre. 
621 
26. 29 
II. 67 
O 
560 
36.71 
22. 77 
* • w 
784 
31-37 
22. 98 
7 * 1 
367 
26. 64 
21. 22 
21. 4 
430 
27. 26 
21. 47 
9 - 7 
536 
13.22 
11.18 
Total annual precipitation.... 
Total seasonal precipitation... 
2 59 
27. 06 
19. 05 
4 2 
47.64 
38.12 
DESCRIPTION OF THE ROTATIONS 
The plots on which these rotation experiments are conducted are X 
acre in size, being 264 feet long by 41.25 feet wide. The longer dimension 
of the plots lies on an east and west line, and the alleys between the plots 
are 4-75 feet wide. When planted to cotton each plot contains 10 rows, 
4.1 feet apart. The rotation plots are arranged in two series which extend 
north and south. Of these series the one on the west is called series A 
and the one on the east series B. A field road some 20 feet wide runs 
along the west side of series A, another separates the series from each 
other, and still another north and south road bounds series B on the east. 
Each series is subdivided by two crossroads, 16 feet wide, so placed that 
each subdivision of a series includes 18 quarter-acre plots. The subdi¬ 
vision or field at the north end of each group is numbered 4, the center 
one is numbered 5, and the one at the south end is numbered 6. Thus, 
field A-4 lies at the northwest corner of this group of six fields, and field 
b fi®s in the southeast corner. The plots in each field are numbered 
from 1 to 18. The regularity of the system just described is broken in 
field A-4 by placing 4 plots whose long dimensions lie on a north and south 
line in the space that should be occupied by the 3 plots, 7, 8, and 9. 
These 4 plots numbered 7, 8, 9, and 10, counting from east to west— 
are each surrounded by a ridge or border to prevent the run-off of water 
during torrential rains. Consequently there are in field A-4 actually 19 
plots instead of 18, as in the other fields. 
This detailed description of the location of these field plots is given so 
that the reader may the better interpret the subsequent notes on the 
field distribution of the rootrot infection. 
