78 QUEENSLAND AGRICULTURAL JOURNAL. {1 Fes., 1902. 
They also produce what is called humic acids, which form humus—that darks | 
coloured product which I told you of, resulting from the decay of vegetable 
matter. It is from this that nitrogen is supplied to the crops. 
Farmyard manure undergoes great changes by being kept for any length 
of time. When it is quite fresh, its constituents are not quite so soluble im 
water as when it has rotted. The consequence is that if the manure, when 
spread on the land, is not immediately required for some crop, its constituents 
will be retained (if the manure is fresh) in a stiff soil until the needful changes” 
take place which enable the manure to part with them. If an immediate effect 
is required to be produced, then well-rotted manure must be used, because 
those changes mentioned have already taken place in it, and the plant food is 
at once available. 
Now, here is a curious thing connected with farmyard manure, which it 18 
well you should know. You may have seen heaps of manure lying in a ‘field, 
‘like a number of great white-ant hills. From what you have just learnt about 
the constituents of this dung, you might be inclined to think that the rain and 
wind would carry off most of the valuable elements it contains, but this is not 
so. Although the constituents of ammonia are present in this “ perfect” 
manure, yet Jt contains no volatile ammonia—that is, ammonia in such a state as 
you find it in a scent bottle, from which it rapidly evaporates. Neither fresh 
nor old manure contains it. So there is nothing for the wind to evaporate 
except water, whilst, if it rains, the soluble salts are washed into the soil where 
they are wanted to be. But if you make these small manure heaps in a yard | 
or in a paddock, intending to cart them away some day, you will find that most 
of their value as a manure is gone, for the salts required for your crop have | 
been washed away by the rain, and have drained away over the yard or across 
the paddock, and so are lost to you. The loss caused in this manner has been 
carefully calculated by agricultural chemists, who have prepared tables showing 
exactly what constituents are lost and how much of each. Some of those tables 
I intend to give to you in a simple form when we shall have finished our first 
lesson on manures. For the present I will only tell you that when farmyard 
manure is left exposed for some, say twelve, months in an open yard, two-thirds 
of its fertilising matters are lost. Thus, if you exposed 9 tons of manure in 
this manner, 6 tons would have disappeared in twelve months. 
You will now answer the following questions:— 
Questions on Lesson 12. 
1. Why is a soil which contains too much of any one constituent a poor 
soil ? 
2. Define peat and marl. 
3. Of what value is marl in agriculture ? 
4. What is meant by farmyard manure ? 
5. Of what is the organic, part of plants composed? Name also the 
substances forming their inorganic parts. 
6. What is the object of applying manure to the land ? 
7. What is one of the most important studies for a farmer ? 
8. Why is farmyard manure better than any other ? 
9. What are natural manures? Whence are they obtained ? 
10. Why is the liquid portion of farmyard manure more valuable as plant 
food than the solid portion ? 
11. What are the inorganic constituents of farmyard manure? What the 
organic ? ; 
12. What do these organic compounds produce when decomposed ? 
13. What kind of manure should be used if an immediate effect is to be 
produced on the crops ? 
14. What would be the result if small heaps of manure were left exposed 
for twelve months in an open yard ? 
