252 THE SYSTEM OF FAEM-YARD MANURING. 



would, for instance, be the height of absurdity to require 

 the tobacco planter who grows his crops on a lime or 

 marl soil, to replace the lime carried off in the leaves of 

 the plant. But it tells him that not all that goes by the 

 name of manure is useful for his fields, and it shows him 

 the difference between manures : it informs him of the 

 loss inflicted upon the soil by the preceding crop, and 

 the supply required to insure future harvests ; it teaches 

 him never to allow himself to be guided in his proceed- 

 ings by the opinions of persons who do not take the 

 slightest interest in him and his land, but always to act 

 upon his own observations. A careful study of the weeds 

 that spring up spontaneously in his fields may frequently 

 prove more useful in this respect than a heap of hand- 

 books on agriculture. 



If after the foregoing statements the condition of the 

 cultivated land in Europe, and the decline towards which 

 agriculture is tending by the prevaihng system of farm- 

 yard manuring, should still be a matter of doubt to 

 many persons unacquainted with the natural sciences, 

 and who trust only to definite numbers as palpable facts, 

 that doubt may, perhaps, be removed by statistical data 

 on the corn produce of the land in different parts of 

 Germany, which have been collected partly by order of 

 the government. 



For a correct appreciation of the importance of these 

 data in the matter, it is necessary in the first place to 

 understand clearly what is meant by an ' average ' crop. 

 By this term is designated the average produce, ex- 

 pressed in numbers, of a field, or a number of fields, or 

 all the fields of a district or country. The figure which 

 represents it is found by adding together the produce of 

 all the fields for a number of years, and dividing the 

 sum total by the latter. There is accordingly a special 



