1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 437 



in the following pages, the physical constitution of root systems 

 may account in part for varying degrees of sensitiveness to cop- 

 per compounds. 



The presence of copper in tops and roots of check is due to 

 0.0025 per cent of copper in the soil which was supposed orig- 

 inally to be free from this element. 



Pot Cultures with Field Soils 

 Two field soils containing copper from irrigating waters 

 were tested in pot culture with reference to toxic effects and 



Fig. 11. — Pot cultures of corn in field soils containing tailings. No. 3887, 

 .027% Cu; no. 3888, .047% Cu ; and no copper. Cultures in field soils are 

 slightly affected. 



copper content of root systems. The soils employed were from 

 a field showing varying effects of accumulations of tailings, im- 

 mediately southeast of Saff'ord : 



Cu 



in soil, 

 Sample pev cent 



3887 Sandy loam, surface 12 in. of soil recently put under irri- 



gation 027 



3888 Heavy clay (tailings) mixed with sandy loam, surface 12 



in., long under irrigation, much tailings 047 



In these two soils, differing mainly through the addition of 

 tailings to No. 3888, cultures of corn, beans, and squash were 

 made, and examined for copper with the following results : 



