12 CIRCULAR 9 5, U. S. DEPARTMENT OF AGRICULTURE 



cut. Downward growth of roots in a was checked by a very heavy 

 bed of gravel and in d by a layer of solid limestone. In b and c, 

 downward growth was completely stopped by the hardpan of the 

 Lebanon soils. In all excavations made in the Ozark area, even in 

 the Baxter and Newtonia soils where roots were found to a depth 

 ranging from 6 to more than 8 feet, downward growth seemed to be 

 stopped by chert or limestone beds. 



In order to determine if possible how deeply apple-tree roots might 

 grow under the most favorable subsoil conditions and if heavy clay 

 subsoils restrict deep growth in other regions as in the Ozarks, a 

 few excavations were made in Knox silt loam, Grundy silt loam, and 

 Summit clay loam in Jackson County, Mo. 



Knox silt loam has a subsoil of uniform, open, silty texture to a 

 great depth and is a productive apple soil. Grundy silt loam and 

 Summit clay loam have heavy, compact clay subsoils and are used 

 to a much less extent for apple growing. In Knox silt loam roots 

 of trees from 20 to 25 years old, at the outer limb spread, were found 

 to a depth of more than 12 feet and many probably grow much 

 deeper. Maximum depth of penetration in the Grundy and Summit 

 soils, on the other hand, was only about 40 inches. (PL 5, B.) The 

 excavation, the roots from which are shown in Plate 5, B &, was ex- 

 tended to a depth of only 10 feet, but several roots were cut off in the 

 bottom and undoubtedly go much deeper. Roots in a are from a 

 Jonathan apple tree 20 years old, in b from a Jonathan probably 

 nearly 30 years old, and in c from a Ben Davis about 25 years old. 

 Roots shown in a and c are from trees on Knox silt loam and in b 

 from Summit clay loam. The roots were treated as were those shown 

 in Plate 5, A. 



CONCLUSIONS 



This study gives conclusive evidence that in the Ozark area of 

 southwest Missouri and northwest Arkansas there is a very definite 

 relation between subsoil conditions and the growth of apple trees; 

 that on soils having open subsoils the tree roots penetrate deeper and 

 that trees grow larger, produce better, and live longer than on soils 

 with tight subsoils; that under favorable subsoil conditions apple 

 trees root deeply, a tree 20 years old sending its roots into and com- 

 manding the moisture and plant-food resources of at least 5,000 cubic 

 feet of soil, whereas on soil with a tight subsoil the supply volume is 

 less than half as great; that root diseases are in many places an 

 accompaniment of bad subsoil conditions; that in this area soils 

 unsuited for orchard planting have been so used largely on account 

 of their level surface, ease of cultivation, and sightliness rather than 

 because of lack of better soils, of which there is a great abundance ; 

 and that the same differences in root development of trees in orchards 

 planted on soils with open subsoils and on soils with tight subsoils 

 exist in other areas as well as in the Ozarks. 



The study, while calling attention to the importance of good care, 

 emphasizes the fact that control of disease, cultivation, and fertiliza- 

 tion, which may seem to overcome the handicap of tight subsoil when 

 the orchard is young, can not overcome it as the trees become older 

 and their demands greater. 



U. S. GOVERNMENT PRINTING OFFICE: 1929 



For sale by the Superintendent of Documents, Washington, D. C. Price 10 cents 





