10 



CIRCULAR NO. 114, BUREAU OF PLANT INDUSTRY. 



Plain. The soil .is mostly the result of weathering of limestone 

 rocks of the Upper Cretaceous period. Recent alluvial deposits have. 

 been washed down from the higher lands northwest of the city, re- 

 sulting in local modifications through the addition of coarser mate- 

 rial. The typical soil is a heavy black or brownish clay or clay loam. 

 The lime content of the soil is unusually high, the proportion of 

 lime in the upper 12 inches of soil varying from 7 to 23 per cent, 

 This lime occurs in the soil both as finely divided material and as 

 gravelly concretions. In the former condition it is generally dark 

 colored through staining by decomposed organic matter, while in 

 the latter condition it is usually white. 



TEST OF SUBSOILING IN ROTATION AND TILLAGE EXPERIMENTS. 



In order to determine the effect of subsoiling upon crop yields and 

 upon the moisture content of the soil at San Antonio, subsoiling 

 tests as a part of the rotation and tillage experiments were begun on 

 the San Antonio Experiment Farm in" the fall of 1009. This rota- 

 tion and tillage work is conducted on 82 plats, each one-fourth acre 

 in size. Three years' results have been obtained with subsoiling, and 

 it is believed that these results are sufficiently conclusive to justify 

 their publication. Corn, cotton, oats, grain sorghums, and sac- 

 charine sorghums are the crops grown in the rotations. The va- 

 rieties of the various crops referred to in this paper are as follows: 

 Corn (Laguna), three years; oats (Appier's Tviistproof), three 

 years; cotton (Triumph)'. 1010 and 1011, (Acala). 1012. 



Those rotations in which subsoiling has been tested are shown in 

 Table I. The lists are so arranged that the rotations opposite each 

 other are directly comparable, the only difference in treatment being 

 that of subsoiling or its omission. 



Table I. Lists of rotations in which subsoiling has been tested at San Antonio 



Experiment Farm. 



Yr. 



Not subsoiled. 



Rotation A5-D: 



i late for grain, cowpeas; plow under cowpeas 

 in fall. 



Cotton; plow in November. 



Com, cowpeas, manure; plow under cowpeas 

 in fall. 



Cotton; plow in November. 

 Rotation A 6- A: 



Corn, plow in July. 



Oats for hay; plow in May. 

 Rotation 15«V A: 



Corn: plow in July. 



Cotton; plow in November, 

 isolation B6-D: 



Corn, cowpeas, manure: plow cowpeas in fall. 



Cotton; plow in November. 

 Rotation B6-I i : 



Corn: plow in February. 



Cotton; plow in February. 



Subsoiled. 



Rotation A5-E: 



' >ats for grain, cowpeas; plow and subsoil in 

 fall. 



Cotton; plow in November. 



Com, cowpeas, manure; plow cowpeas and 

 subsoil in fall. 



Cotton; plow in November. 

 Rotation A6-C: 



Corn; plow in July. 



< »ats for hay; plow and subsoil in May. 

 Rotation B6-B': 



Corn: plow and subsoil in July. 



Coll on: plow and subsoil in November. 

 notation B6-E: 



Corn, cowpeas, manure; plow cowpeas in fall. 



Cotton; plow and subsoil in November. 

 Rotation lie. II: 



Com; plow and subsoil in February. 



Cotton; plow and subsoil in February. 



[Cir. 114] 



