134 PRACTICAL FARM CHEMISTRY. 



As no return is made for the large quantities of 

 nitrogen and potash which the crops remove, while 

 phosphoric acid is put into the soil every year in 

 larger quantities even than needed for the grain 

 growth, the land must in the end get very hungry 

 for just the two substances of plant food which phos- 

 phates do not provide, and the crops must suffer for 

 the lack of them. To remedy the deficiency in such 

 case, we might apply potash and nitrogen, each in 

 some simple form — potash in German potash salts, 

 green sand marl, ashes, etc; nitrogen in nitrate of 

 soda, sulphate of ammonia, etc., or both plant foods 

 combined in saltpetre waste from gunpowder works, 

 in sea weed, tobacco stems, wool waste, etc.; or 

 better than all this, we might resume the old way 

 of manuring with barnyard manure, until the 

 original balance of soil fertility is restored. If this 

 treatment is again pushed still further, the time 

 soon comes when plain phosphate will once more 

 show good results. All this seems as plain as a 

 simple example in addition and subtraction. 



A proper rotation of manures and manurial sub- 

 stances is as important in profitable crop feeding as 

 the proper rotation of the crops themselves. Our 

 chief aim must be the maintainance of a well- 

 balanced soil fertility. 



