May 2,1921 
Cotton Rootrot in the San Antonio Rotations 
121 
This tabular statement shows that these continuously cropped cotton 
plots have all suffered severely from rootrot. As has been the case with 
all the plots in the rotations, the disease has become increasingly serious 
during the later years. The two plots that have had identical treatment, 
A-6-3 and B-5-3, show wide differences in extent of infection, but this 
may be due in part to situation, as they are in different parts of the field. 
The plots B-5-3 and B-5-4 lie side by side. Their tillage treatment has 
differed only in that B-5-4 has received annual applications of manure. 
It is not clear that this difference in treatment is responsible for the 
difference in results, but it may be a contributing factor. It is clear, 
however, that in A-4-19 the annual use of a green manure crop of field 
peas plowed under has not been strikingly effective in controlling the 
disease. 
THE TWO-YEAR ROTATIONS 
The second category of rotations includes those in which cotton 
recurs on the same land each alternate year. The extent of rootrot 
injury in these 20 two-year rotations is shown in Table III. 
The outstanding feature of Table III is the wide variation in the ex¬ 
tent of rootrot injury in these different rotations, a range in means from 
0.8 per cent to 31.9 per cent. If there were reason for believing that 
these differences in rootrot injury were associated with differences in till¬ 
age methods or with different crop sequences, it would appear that the 
remedy for the disease was to be sought through the adoption of the 
tillage and rotation methods which have shown the least injury through 
the period of years. But, unfortunately, a critical study of the facts 
does not warrant such a conclusion. It is only by detailed analysis of 
the facts involved that the real significance of the results can be under¬ 
stood. For such a detailed study it may be expedient to separate these 
20 rotations into groups with respect to some significant feature of the 
tillage or rotation practice, as follows. 
1. Long period oe eaeeow. —Rotation A~4a, cotton grown on land in 
alternate years, the land being plowed immediately after the crop is 
picked and kept in clean fallow for about 16 months until the next 
cotton crop is planted. The history of this rotation shows that very 
little rootrot developed prior to 1915 but that the injury has been severe 
during 1918 and 1919. This rotation may be compared directly with 
A-6-3 and B-5-3, which differ from it only in the length of fallow period, 
this being 16 months in the first case and 4 months in the other two cases. 
The mean rootrot injury was 10.5 per cent for the long fallow period and 
6.7 and 42.2 percent for the two short fallow periods. Obviously, the 
longer fallow period has not shown a definite improvement of condition. 
2. Corn, sorghum, and oats as intervening crops.— Of the 19 
two-year rotations which include another field crop, 10 include corn, 
6 include sorghum, and 3 include oats. If we disregard all other features 
of tillage and rotation practice, we find that the 10 rotations, including 
