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SECOND BOOK. 
way they are of great service, because nitrogen is 
one of the chief foods that plants must have in 
the soil. 
4. Even better than green manure, though not so 
ready to hand, is that which consists of the partly 
rotten straw, or litter, which has been well trodden 
by cattle and other animals. This kind of manure 
contains all the substances that plants need. It 
even holds some food quite ready for the plants, and 
it will provide much more as it decays in the ground. 
5. You know how rotten fruits will cause the 
sound ones with which they are packed to become 
rotten like themselves. In the same way the 
decaying manure acts on what is in the soil, caus-. 
ing changes to take place, whereby fresh plant-food 
is prepared for use. 
6. It may happen that our soil is poor in some 
particular kind of food, or perhaps that kind has 
been used up very fast by the crop that has been 
raised. When that is the case we may help the 
soil to make up whatever plant-food has run short 
by using some ‘ special ’ manure. 
7 . Amongst such manures the best known are 
guano (the dung of sea-birds), crushed bones, and 
wood ashes. Of course we choose the one that will 
either supply the kind of food that is needed, or 
will cause the land to produce it quickly. 
8. The green manure or the farm-yard litter, 
however, does more for the soil than provide it 
