CHAPTER XVII.

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.