8 PLANT PRODUCTS 



Much of the disfavour into which so-called chemical 

 manures fell in the early efforts to use them was due to 

 injudicious and ignorant use. Probably no one would to-day 

 make the same mistakes, but to a lower degree similar 

 mistakes are still made. Very large areas of land in many 

 countries are urgently in need of dressings of lime, because 

 all kinds of fertilizers have been used in the past, with only 

 a partial recognition of the important fact that most ferti- 

 lizers remove lime from the soil. In the early days of inten- 

 sive farming lime was used generously and often excessively. 

 No doubt the disastrous effects of excessive use of lime 

 made farmers rush to the opposite extreme, and use far too 

 little lime. To-day we have to make up for past neglect. 

 Even on soils which stand over chalk or other calcareous 

 geological formations, lime is not infrequently advantageous. 



All life depends on a delicate balance of chemical reactions, 

 and although living things have a considerable power of 

 resistance, if one is merely considering them from the 

 point of view of the struggle for existence, yet when one is 

 considering the growth of plants from the point of view of 

 obtaining a paying crop, one cannot permit them to struggle, 

 one must supply them with the balance which they require. 

 Unfortunately, this problem of the balance of the ingredients 

 needed by the plants has received too little attention. 

 The way in which the balance of a soil may be upset is shown 

 in the following graph, which is taken from a paper by the 

 author, read to the Society of Chemical Industry, May 31, 

 1915. This graph shows, with regard to the two constituents 

 selected for illustration, that when the fertilizing dressing 

 of magnesia or manganese increased, an increase in crop 

 occurred at first, but after moderate percentages of the 

 fertilizing ingredients had been used, a decrease in crop 

 occurred. There are any number of illustrations of the 

 same law, in other subjects dealing with the life of -plants 

 or animals. 



All the more recent books to be found in the bibliography, 

 have some reference to the principle that the balance of 

 the ingredients is an important proposition. 



