382 QUEENSLAND AGRICULTURAL JOURNAL. [1 Oor., 1899. 
much larger weight of fruit produced in good bearing orchards more than makes 
up for the deficiency, and the call on the potash is often as great, if not greater, 
than these fruits, prunes excepted. If kainit is used in the place of sulphate 0 
potash, from 6 ewt. to 8 ewt. per acre will be necessary. In most cases potas 
manures are most advantageously applied in conjunction with phosphatic and 
nitrogenous manures, as few soils simply require potash without the other 
ingredients. 
The composition and application of manures required for different erop® 
will be dealt with later on, when the two remaining essential elements of plant 
food have been described. 
PHOSPHORUS. 
Phosphorus, or, as it is generally spoken of in manuring, phosphoric acid, 18 
essential to the growth of all fruits, occurring in the seeds in far larger amounts 
relatively than in the flesh, in which respect it is similar to nitrogen. It 18 
owing to this that the thinning of stone fruits has such a beneficial effect on the 
tree, in addition to the mere increase in size of the fruit allowed to remain. AS 
when a peach or an apricot is allowed to bear an excessive number of small 
fruits, the crop, besides being comparatively worthless, will have so weakene 
the tree, and made such a call on the soil, that it will take a year’s rest to 
recuperate, whereas, where judicious thinning is practised, the tree will produce 
annually a greater weight of first-class fruit that will do less damage to the tree 
and soil than the great number of small worthless fruit and the great crop of 
stones. 
Fruits do not take anything like as much phosphoric acid out of the soil as 
they do potash; nevertheless, as there is a very sai smaller supply of available 
hosphorie acid in most soils than there is potash, it is usually the first inorganle 
plant food to become exhausted. 
Phosphoric acid is always found present in large quantities in the seeds of 
plants; hence the growing of wheat, barley, oats, beans, or maize for grain year 
after year, without manuring, rapidly reduces the available proportion of this 
plant food in the soil. Any deficiency of phosphoric acid in the soil is show? 
by the failure of the crop to produce seed. Thus wheat, barley, oats, sorghum, 
or corn may grow plenty of fodder, but at the same time produce no grain, and 
potatoes and root-crops may produce plenty of tops, but no tubers or roots ; oF 
a fruit tree, owing to an insufficient supply, may only bear a small crop of fruit, 
and that of poor quality, so that it is not usually a difficult: matter to TV otermine 
whether a soil requires a dressing of phosphates or not. 
Phosphoric acid is derived principally from the following sources :—Bones, 
_ phosphatic guanos, coprolites, and basic slag. As far as this colony is con- 
cerned, bones are practically the only source to be considered, though basic slag 
is proving a cheap source in England, but is relatively dearer than bones 10 
this colony. Bones may be either applied in the form of bonemeal, when the 
phosphoric acid contained in them is combined with lime in an insoluble form 
that is only slowly available for plant food by being rendered soluble by the 
carbon di-oxide in the water of the soil, or they may be applied in the form 0 
superphosphate, when the phosphoric acid is in a soluble and readily available 
form for plant food. 
Superphosphate is formed by the action of sulphuric acid (oil of vitriol) 0? 
bones, or any other form of insoluble phosphate, converting the insoluble int? 
soluble phosphates. ‘The relative value of these two forms of phosphoric act 
is estimated at 2s. per unit for the insoluble, and 5s, 4d, per unit for the soluble. 
Where a rapid growth and a quick return is required, as in the case of vegetables, 
the soluble form should be used, but where a lasting effect is required use te 
insoluble. In the case of fruit trees the two forms are best used together, aC 
as to produce the best effects, as the soluble phosphates stimulate a. sap 
growth, and when their effect is past the trees have the more lasting forty) t9 I 
back on. It is often a good plan to apply the insoluble form dutill# the 
vutumn, so that it may become stake acted on in the soil, and be teady for the 
