514 University of California Publications in Agricultural Sciences [Vol. 1 



Zinc Sulfate — Greenhouse Soil 



Only the greenhouse soil was employed to test the effect of 

 ZnSO^ on barley plants. As was the ease with CuSO^ on the 

 same soil, three successive crops were grown, two treatments of 

 ZnSO^ being given. The results obtained, together with the 

 treatments given, are indicated in tables Ya, Yh, and Vc. 



First Crop 

 A study of table Ya reveals the fact that ZnSO^ in the case 

 of the first crop of barley is not unlike CuSO^ in its action. In 

 other words, while the latter salt exercises a greater and more 

 definite stimulating action in the first crop, ZnS04 also manifests 

 a definite though smaller stimulating effect on the barley plants. 

 This seems to be supported by the fact that only eight pots out 

 of thirty treated with varying amounts of ZnSO^ give a smaller 

 yield than the highest yield of the control pots. In general, the 

 stimulation seems to be greatest at concentrations of ZnSO^ 

 varying from 500 p. p. m. to 1200 p. p. m. inclusive. This state- 

 ment has reference only to the total yield of dry matter and 

 not to any parts, like roots or tops, taken separately. On 

 the same bases, also, no definitely toxic effect of ZnSO^ was 

 observed, though, as above intimated, some apparent effects of 

 that nature were noted. Again, in accord with the results 

 obtained with CuSO^ no grain worth weighing was produced in 

 the first crop, and the weights of the straw given in the table 

 therefore include such partially formed heads as were developed. 

 In still further agreement with the results of the first crop of 

 the CuSO^ series, ZnS04 stimulated the growth and develop- 

 ment of roots practically throughout the whole series. The 

 stimulation to root development alone was, however, greater 

 in the ZnS04 series than in the CuSO^ series, just as the opposite 

 was true for the tops. The greatest stimulation to root develop- 

 ment appears to have been attained at the higher rather than 

 at the lower concentrations of ZnSO^, the difference being most 

 marked in that respect between the first three concentrations 

 employed and the rest. This circumstance, as will be seen by 

 a comparison of table Ya with table Ila, is the reverse of that 

 noted in the first crop of the CuSO^ series, in which the first four 



