12 



CIRCULAR NO. 



114, BUREAU OF PLANT INDUSTRY. 



RESIDUAL EFFECT OF SUBSOILING ON THE YIELDS OF CORN AND 



COTTON. 



In order to call attention to the possible residual effect of subsoil- 

 ing on succeeding crops for several years after the operation, Table 

 III has been compiled to show the effect of subsoiling on the yields 

 of corn and cotton where the length of time intervening between the 

 time of subsoiling and that of planting varies from 1 to 16 months. 



Table III.— Effect of different lengths of time between subsoiling and planting 

 on the average yield of corn and vOlton at the Han Antonio Experiment 

 Fa rm. 



There is a marked decrease in the yields of both corn and cotton 

 where the subsoiling was done from 1 to 2 months before planting, 

 and a decrease where the subsoiling was done from 3 to 8 months 

 before planting, while when the subsoiling was done from 15 to 10 

 months before planting there was a very slight increase. While 

 these results are not at all conclusive, owing to the fact that the 

 experiments cover only two years and the number of plats is limited, 

 yet they are suggestive. The figures in this table indicate that loosen- 

 ing the subsoil is detrimental the first few months and also at the 

 end of over a year, when under ordinary conditions if there was to 

 be any resulting benefit it should be apparent. During the interven- 

 ing period between subsoiling and planting, a crop was grown and 

 the land replowed, and it would be supposed that any unfavorable 

 soil conditions brought about by subsoiling would have time to read- 

 just themselves during the period. Yet the increase in average yields 

 as shown by the table is so slight as to indicate very little result- 

 ing benefit from the operation. In no case was the increase sufficient 

 to cover the expense of subsoiling. 

 EFFECT OF SUBSOILING ON THE MOISTURE CONTENT OF THE SOIL. 



Determinations of soil moisture were made at regular intervals of 

 about one month on rotations B6-A and BG-B for a period of two 

 years. Table IV shows the percentage of moisture in plat B6-1 as 

 compared with B6-3, and BG-2 as compared with B6-4; also the 

 crops grown on each plat each year and the time of plowing or 

 subsoiling. The soil samples for moisture determinations were taken 

 by means of the standard soil tube, two cores being taken on each 

 plat and composited to a single sample. This composite sample 

 was then weighed, dried, and weighed again, and the percentage of 

 moisture computed on the basis of dry soil. 



[C'ir. 114] 



