176 SOILS AND MANUEES 



difference between purchased fertilisers and feeding stuffs 

 on the one hand, and farmyard manure and food for 

 animals grown on the farm on the other. The former is 

 something added to the land, i.e., introduced into the cycle ; 

 the latter is merely a means of restoring to the land what 

 had been previously taken out of it, i.e., a stage in the 

 cycle of changes which might, theoretically, go on for ever 

 without gain or loss, except by the conversion of plant 

 food into the available state in the soil and by the sale of 

 produce. If the whole of the increase due to the use of 

 purchased manures and feeding stuffs be sold, the fertility 

 of the soil will not be increased. It is sometimes said that 

 more cannot be got out of the soil than is put in. 

 This is not so. The produce of the land may be equal to 

 what is put in plus what becomes available in the same 

 time. 



Conservation of Matter. The facts quoted above form 

 an illustration of the law of conservation of matter. It 

 asserts that " the total quantity of matter is not altered 

 by the changes that it undergoes." It is one of the funda- 

 mental laws of nature, and applies equally to physical, 

 chemical and biological changes. Most farmers are more 

 or less conscious of the operation of this law in regard to 

 agriculture, but they sometimes fail to realise its full im- 

 portance. The weight of the crops is usually so much 

 greater than that of the seed sown, as almost to make it 

 appear as if something had been formed out of nothing. 

 The truth is, of course, that the plants have merely trans- 

 formed materials which they have collected from the air 

 and from the soil. One hears occasionally of men keeping 

 more stock than they can properly feed, in order to make 

 manure. It is quite certain that nothing comes out of 

 the animals that has not previously gone in. The animals 

 transform the constituents of the food into meat, milk, 

 wool, etc., but they do not produce these things out of 



