506 University of California Publications i7i Agricultural Sciences [Vol. 1 



three successive crops on the same soil, only one of them, the 

 third, was influenced purely by the residual effects of the CuSO^ 

 application remaining after the production of one crop. With 

 these observations in mind, let us now consider the results of 

 the CUSO4 applications in the three crops harvested on the 

 greenhouse soil. 



First Crop 

 The growth of the plants in the first crop was very rank in 

 the controls as well as in the treated pots, with the result that 

 high jdelds of dry matter were obtained. This was doubtless due 

 to a large supply of available plant food in the fresh greenhouse 

 soil and especially to the high nitrate content and high nitrify- 

 ing power of the soil. The deep green color of the leaves, above 

 referred to and the tendency shown by the plants to lodge seem 

 to confirm this view, and it is further supported by nitrification 

 studies which we carried out and which are reported below. 

 Because of the conditions for rank growth, however, the 

 growing season was lengthened and scarcely any grain was pro- 

 duced. The data of the first section of table II therefore give 

 only the yields of straw and roots. Despite considerable dis- 

 crepancy among the yields of duplicate pots, there can be no 

 question after an examination of the data for the first crop that 

 CuSO^, in the concentrations and under the conditions employed, 

 has caused the barley to produce more dry matter than was pro- 

 duced in the control pots. Such stimulated growth is apparent 

 throughout the whole series of copper concentrations varying 

 from 50 p. p. m. to 1500 p. p. m. Concentrations above 1000 p. p. 

 m. seem to l)e definitely more toxic, or at least less stimulating, to 

 the barley plants than lower concentrations if average yields are 

 adopted as criteria. Such procedure may, however, be unjusti- 

 fiable because of the large discrepancies among the yields of 

 duplicate pots. That the increases in yields of dry matter of 

 barley are real and not accidental is evidenced not onh' by their 

 manifestation in the whole series, but also by the magnitude of 

 the increases involved. Thus in the concentration of 600 p. p. m. 

 CUSO4 an increase in yield over that of the control pot was 

 obtained which was equivalent to nearly 50 per cent of the total 



