EFFECT OF COMMON SALT. 319 



or in combination with common salt, exert a favourable 

 influence upon the increase of the crops. 



The land in Weihenstephan is peculiarly suited for 

 the cultivation of barley. Field A, after a manuring 

 of the ordinary kind, about 600 cwt. per hectare, had 

 borne turnips in 1854, peas in 1855, and wheat in 1856 ; 

 it was then intended to let it lie fallow for one year, 

 and to dress it at the end. of the year for a new crop. 

 On the other hand, Field B, before the experiment was 

 made, had already borne four crops, namely, rape, 

 wheat, clover grass, and oats ; and was, in comparison 

 with the first field, more exhausted, and by means of 

 the oats and clover made much poorer in nutritive sub- 

 stances for the following cereal crop. 



This seems to afford an explanation of the striking 

 fact, that in 185T the nitrates exercised upon the field 

 a far more favourable influence than guano, although 

 the soil had received as much nitrogen in the guano as 

 in the nitrates, with the addition of phosphoric acid 

 and potash. The field was still rich enough in nutri- 

 tive substances for a good barley crop, and merely 

 required their more uniform distribution (which was 

 effected by the nitrates and the common salt), in order 

 to make available to the roots of the barley plants as 

 much or even more food than was the case with the 

 plot manured with guano, on which the sum of the nutri- 

 tive substances was greater. 



In estimating the results of these experiments we 

 must take into account the fact established by Dr. 

 Zoeller, that soda seems to take a definite part in the 

 production of barley seed. It is clear that the nitrates 

 used did not simply act as agents in distributing other 

 nutritive substances, but the soda as well as the nitric 

 acid had their own share in the production of the crop. 

 In the fourth experiment the field received as much 

 nitric acid as in the second, but the base combined 

 with the acid was potash and not soda ; and in the 

 fifth experiment the addition of common salt produced 

 a remarkable increase in the corn crop. However, in 

 the third and fifth experiments the quantity of salt ap- 



