222 THE SYSTEM OP FARM-YAKD MANURING. 



In the produce of cereals there is only one proper pro- 

 portion between grain and straw ; but the unfavourable 

 proportions are many. It is clear that the mass and 

 extent of the organs for the formation of grain (in other 

 words, the bulk of the straw) must bear a definite relation 

 to the product, that is, to the quantity of grain produced : 

 any excess or deficiency in the amount of straw must 

 always act injuriously upon the grain crop. 



When it is known that, on a given field, one part by 

 weight of corn to two parts by weight of straw is the 

 most favourable proportion for the production of grain, 

 then, according to theory, the manuring of the field should 

 not be such as to cause any marked alteration of this 

 relative proportion in the increased produce ; that is to 

 say, the several manuring substances should be selected 

 and laid upon the field in such quantity and relative pro- 

 portion, that the composition of the soil may remain the 

 same as it was before. 



It is weU known that certain manuring substances are 

 especially favourable to the formation of the herbaceous 

 parts of plants, others to that of seed. Phosphates, as a 

 general rule, increase the gram crop : whilst of gypsum 

 it is well known that where that substance effects an 

 increase in the produce of clover-hay, this increase is 

 always attended mth a marked diminution in the produce 

 of seed. The cultivation of potatoes or Jerusalem artichokes 

 tends to reduce the excessive accumulation m the arable 

 surface soil, of substances which promote the formation of 

 the herbaceous parts of plants. Theoretically, therefore, 

 it is not impossible to maintain a certain uniformity of 

 composition in the soil of a field ; but this cannot be 



effects resulting to land on wliich this product has been cultivated, are 

 too well kno-\^Ti.' The effects must have reference to fields which had 

 been adequately manured, for otherwise no profitable retm-ns can be 

 expected. 



