EGYPTIAN COTTON AS AFFECTED BY SOIL VARIATIONS. 1 



By Thomas H. Kearney, Physiologist in Change of Alkali and Drought Resistant 



Plant Investigations. 



INTRODUCTION. 



Observation of the growth of Egyptian cotton in irrigated soils of 

 the southwestern United States for several years past has shown that 

 this plant is decidedly sensitive to variations in its physical environ- 

 ment. Differences in the texture, and consequently in the moisture- 

 holding capacity of the soil, are easily detected from the accompany- 

 ing differences in the size, appearance, and f ruitf ulness of the plants, in 

 the size of the bolls, and in the quality of the fiber. The presence of 

 alkali salts in the soil also induces marked differences in the growth 

 and behavior of the cotton plants. It is evident that in order to 

 obtain the largest yields and, what is of the utmost importance, the 

 greatest possible uniformity in the staple, strength, and other quali- 

 ties of the fiber, Egyptian cotton must be grown in soils that do not 

 vary greatly in texture and salt content. 



MOISTURE CAPACITY OF THE SOIL. 



In many plantings of Egyptian cotton which have been made on 

 recently cleared land the fields have appeared more or less spotted, 

 the plants in some places being smaller, more erect, and lighter col- 

 ored, with fewer and smaller bolls and shorter, often weaker, fiber 

 than in other places. Marked differences of this kind frequently 

 appear within distances of a few feet. A field of the Yuma variety 

 on the United States Experiment Farm at Bard, CaL, in 1911 showed 

 conspicuous local differences in the growth and appearance of the 

 plants. Soil samples were therefore collected at a number of differ- 

 ent points corresponding to various stages in the size and condition 

 of the plants. 



Upon making the borings it was at once evident that the variations 

 in growth of the plants were closely correlated with variations in the 

 depth of the blanket of silt loam which overlaid a subsoil of coarse, 

 light-colored sand. The depth of the silty layer varied from 5 to 18 

 inches in different parts of the field. Where it was thinnest the plants 

 were poorest, and vice versa. 



The moisture-holding capacity of these two soils was widely dif- 

 ferent, that of the silt loam being high, as indicated by a moisture 



i Issued Feb. 8, 1913. 



17 



