1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 435 



TABLE XX 

 Chalcocite Series (1908) 



Appear- 



Cu ance and Dry Cu Cu p. p.m. in 



Sample in soil, height matter, found, , ■'' , 



No. Culture per cent of plants grams grams tops roots 



Normal 



3979 Corn Check* 36 in. 17.60 .00026 15.00 



3979c Corn Cheek* 4.62 .00027 58.00 



3980 Corn .01 33 11.60 .00011 10.00 



3980c Corn .01 2.94 .00023 78.00 



3981 Corn .02 38 19.40 .00021 11.00 



3981c Corn .02 6.14 .00114 186.00 



3982 Corn .03 35 17.90 .00028 16.00 



3982c Corn .03 6.99 .00176 252.00 



3968 Corn .05 45 51.70 .00065 13.00 



3978 Corn .05 6.14 .00105 171.00 



Toxic effects begin at about .08% Cu in soil. 



Stunted 



3983 Corn .10 36 in. 14.00 .00031 22.00 



3983c Corn .10 yellow 6.08 .00625 1028.00 



3984 Corn _ .50 8 in. 3.20 .00040 125.00 



3984c Corn .50 .47 .00065 1383.00 



3985 Corn 1.00 12 3.20 .00050 1.59.00 



3985c Corn 1.00 .49 .00089 1816.00 



* Containing traces of coppei', .0025%. 



The cultures described in the foregoing tables indicate sev- 

 eral interesting facts more or less applicable to field conditions. 



(1) Precipitated carbonate of copper is shown to have a 

 nuich more toxic effect npon corn than the finely pulverized 

 ores of chalcocite or chrysocolla. With the precipitated car- 

 bonate 0.025 per cent in the soil was distinctly toxic, while with 

 chalcocite and chrj^socolla about 0.08 per cent was required to 

 produce an equal effect. Inasmuch as all of these combinations 

 of copper may occur in a soil subject to mining detritus, a mere 

 determination of total copper in soils containing doubtfully toxic 

 quantities cannot convey trustworthy information as to the in- 

 juriousness of the amounts present. 



Moreover, since it has been shown that in the case of pre- 

 cipitated carbonate, and sulphate of copper, equivalent quantities 

 of these salts in solution are equally toxic, it is probable that the 

 greater toxicity of the carbonate is due to its greater solubility 

 under soil conditions. It is, in fact, shown in table I, ' ' Solubili- 



