* 1 Ocr., 1899.] QUEENSLAND AGRICULTURAL JOURNAL. . 383 
@ applied except at a time that the plant ean absorb them—that is to say, 
uring a period of active growth. 
In addition to the insoluble and water soluble phosphates or superphos- 
phate, there is a third form which is more active than insoluble and less active 
than superphosphate, which was known for some time as bi-phosphate or reduced 
Phosphate, but which is now known as citrate soluble phosphate, and is given a 
value of 4s. 6d. per unit. 
Personally, I do not object to a certain proportion of citrate soluble 
Phosphate in a phosphatic manure, but look upon it as an advantage in the case 
of slow-growing crops rather than a disadvantage. Except with excessive rains 
or very sandy porous soils, phosphates are not often washed out of the soil, but 
ire retained till assimilated by the tree or plant to which they have been applied. 
The quantity of phosphoric acid removed by 1,000 Ib. of any given fruit, 
Vegetable, or farm crop can be seen by referring to the table at the end of this 
article ; and the quantities required for different fruits and crops used either by 
itself or in conjunction with potash or nitrogen, or both, will be dealt with later 
on when treating of the composition and application of manures. 
plant-growth in spring ; but the soluble form, or superphosphates, should never 
d 
Nirrogen. 
We now come to the last of the essential plant foods that we have to 
Consider, and, though last, by no means the least important or least expensive 
to supply to the soil when it is present in a deficient amount, for though about 
four-fifths of the air consists of nitrogen, still it is not available for plant food, 
except in the case of certain varieties of leguminous plants. In fact, itis the 
most expensive element we have to supply to the soil, its value at the present 
time being about 10s. per unit. Nitrogen occurs in all plants, and is absolutely 
essential to their proper development. It occurs principally in the albuminous 
Matter of fruits, of which it forms about one-sixth, and by far the greater 
Portion of the albuminous matter of fruits is contained in the seeds or kernels, 
‘nd not in the flesh, hence the value of thinning, as previously pointed out, as 
Y judicious thinning you produce as large an amount of flesh and as small an 
amount of seeds (stones) as possible, thereby greatly reducing the amount of 
ma required. 
4 nly a comparatively small proportion of the nitrogen contained in plants 
1s present in the form of nitrates in the ash, the bulk being in the form of 
albuminoids or flesh-forming matter, which form a large proportion of the seeds 
of our farm crops, especially of pulses. It is also present to a considerable 
amount in fodder plants of all kinds, especially in all plants of the pea family, 
Which includes lucerne, clover, cow peas, peas and. beans of all kinds. h 
Nitrogen occurs in the soil in the form of nitrates which are found in 
Conjunction with the organic matter of the soil, which has the power of 
Converting ammonia, the form in which nitrogen is usually applied to the soil, 
into nitrie acid, which forms in conjunction with the potash and soda, &e., in the 
Soil what are termed “nitrates,” and these nitrates are taken up by the tree and 
‘ssimilated, 
There are many sources of nitrogen, but of these only three may be 
Considered as of paramount importance in_ this colony, viz. :—Sulphate of 
ammonia; dried blood; and nipho, a by-product from boiling-down and meat- 
Works containing about 123 per cent. of nitrogen. Nitrogen may also be obtained 
in the form of nitrate of soda and nitrate of potash, which, though they are more 
"eadily available as plant food than sulphate of ammonia, as they have not to 
“ndergo the process of nitrification, are still too dear, when compared with 
Sulphate of ammonia, to be used extensively. Nitrogen also occurs in smaller 
Proportions in many substances that are used as manures, and. of these guano, 
specially Peruvian guano, was at one time the great source of the supply of this 
Material, but the deposits are now pretty well played out, and are of more value 
°r the phosphates than the nitrogen they contain. Bonemeal also contains 
Tom 2 to 4 per cent. of nitrogen, the amount depending on the amount of gluey — 
