SOLUBLE PHOSPHATES IN FARMYARD MANURE.
There is one thing in these experiments of Dr. Vœlcker’s which deserves
special attention, and that is the comparatively large amount of
_soluble phosphate of lime_ in the ash of farm-yard manure. I do not
think the fact is generally known. In estimating the value of animal
manures, as compared with artificial manures, it is usually assumed that
the phosphates in the former are insoluble, and, therefore, of less
value than the soluble phosphates in superphosphate of lime and other
artificial manures.
Dr. Vœlcker found in the ash of _fresh_ farm-yard manure, phosphoric
acid equal to 12.23 per cent of phosphate of lime, and of this 5.35 was
_soluble_ phosphate of lime.
In the ash of well-rotted manure, he found phosphoric acid equal to
12.11 per cent of phosphate of lime, and of this, 4.75 was soluble
phosphate of lime.
“That is, indeed, an important fact,” said the Doctor, “but I thought
Professor Vœlcker claimed that ‘during the fermentation of dung, the
phosphate of lime which it contains is rendered more soluble than in
fresh manure.’”
“He did say so,” I replied, “and it may be true, but the above figures
do not seem to prove it. When he wrote the sentence you have quoted, he
probably had reference to the fact that he found more soluble phosphate
of lime in rotted manure than in fresh manure. Thus, he found in 5 tons
of fresh and 5 tons of rotted, manure, the following ingredients:
SP: Soluble Phosphate of Lime.
IP: Insoluble phosphates.
TP: Total Phosphates.
TSA: Total Soluble Ash.
TIA: Total Insoluble Ash.
TA: Total Ash.
--------------+-----+-----+-----+-------------+-----+-----+-----
| | | | Potash | | |
5 Tons. | SP | IP | TP +------+------+ TSA | TIA | TA
(10,000 LBS.) | | | | Sol. |Insol.| | |
--------------+-----+-----+-----+------+------+-----+-----+-----
Fresh manure | 29.9| 38.6| 68.5| 57.3 | 9.9 | 154 | 405 | 559
Rotted manure | 38.2|57.3 |95.5 | 44.6 | 4.5 | 147 | 658 | 805
--------------+-----+-----+-----+------+------+-----+-----+-----
“It will be seen from the above figures that _rotted manure contains
more soluble phosphate of lime than fresh manure_.
“But it does not follow from this fact that any of the insoluble
phosphates in fresh manure have been rendered soluble during the
fermentation of the manure.
“There are more insoluble phosphates in the rotted manure than in the
fresh, but we do not conclude from this fact that any of the phosphates
have been rendered insoluble during the process of fermentation--neither
are we warranted in concluding that any of them have been rendered
soluble, simply because we find more soluble phosphates in the rotted
manure.”
“Very true,” said the Doctor, “but it has been shown that _in the heap_
of manure, during fermentation, there was an _actual increase_ of
soluble mineral matter during the first six months, and, to say the
least, it is highly probable that some of this increase of soluble
mineral matter contained more or less soluble phosphates, and perhaps
Dr. Vœlcker had some facts to show that such was the case, although he
may not have published them. At any rate, he evidently thinks that the
phosphates in manure are rendered more soluble by fermentation.”
“Perhaps,” said I, “we can not do better than to let the matter rest in
that form. I am merely anxious not to draw definite conclusions from the
facts which the facts do not positively prove. I am strongly in favor of
fermenting manure, and should be glad to have it shown that fermentation
does actually convert insoluble phosphates into a soluble form.”
There is one thing, however, that these experiments clearly prove, and
that is, that there is a far larger quantity of _soluble_ phosphates in
manure than is generally supposed. Of the total phosphoric acid in the
fresh manure, 43 per cent is in a soluble condition; and in the rotted
manure, 40 per cent is soluble.
This is an important fact, and one which is generally overlooked. It
enhances the value of farm-yard or stable manure, as compared with
artificial manures. But of this we may have more to say when we come to
that part of the subject. I want to make one remark. I think there can
be little doubt that the proportion of soluble phosphates is greater in
rich manure, made from grain-fed animals, than in poor manure made
principally from straw. In other words, of 100 lbs. of total phosphoric
acid, more of it would be in a soluble condition in the rich than in the
poor manure.