For nineteen years, 1852 to 1870, some of the plots have received the same manure year after year. The following shows the average yield for the nineteen years:
| Wheat per acre. | Straw per acre. | ||
|---|---|---|---|
| Plot 5. | Mixed mineral manure, alone | 17 bus. | 15 cwt. |
| ” 6. | Mixed mineral manure, and 200 lbs. ammoniacal salts | 27 bus. | 25 cwt. |
| ” 7. | Mixed mineral manure, and 400 lbs. ammoniacal salts | 36 bus. | 36 cwt. |
| ” 9. | Mixed mineral manure, and 550 lbs. nitrate of soda | 37 bus. | 41 cwt. |
| ” 2. | 14 tons farm-yard dung | 36 bus. | 34 cwt. |
The 14 tons (31,360 lbs.) of farm-yard manure contained about 8,540 lbs. organic matter, 868 lbs. mineral matter, and 200 lbs. nitrogen. The 400 lbs. of ammoniacal salts, and the 550 lbs. nitrate of soda, each contained 82 lbs. of nitrogen; and it will be seen that this 82 lbs. of nitrogen produced as great an effect as the 200 lbs. of nitrogen in barn-yard manure.
Similar experiments have been made on barley, with even more striking results. The plot dressed with 300 lbs. superphosphate of lime, and 200 lbs. ammoniacal salts per acre, produced as large a crop as 14 tons of farm-yard manure. The average yield of barley for nineteen crops grown on the same land each year was 48 bus. and 28 cwt. of straw per acre on both plots. In other words, 41 lbs. of nitrogen, in ammoniacal salts, produced as great an effect as 200 lbs. of nitrogen in farm-yard manure! During the nineteen years, one plot had received 162,260 lbs. of organic matter, 16,492 lbs. of mineral matter, and 3,800 lbs. of nitrogen; while the other had received only 5,700 lbs. mineral matter, and 779 lbs. of nitrogen—and yet one has produced as large a crop as the other.
Why this difference? It will not do to say that more nitrogen was applied in the farm-yard manure than was needed. Mr. Lawes says: “For some years, an amount of ammonia-salts, containing 82 lbs. of nitrogen, was applied to one series of plots (of barley), but this was found to be too much, the crop generally being too heavy and laid. Yet probably about 200 lbs. of nitrogen was annually supplied in the dung, but with it there was no over-luxuriance, and no more crop, than where 41 lbs. of nitrogen was supplied in the form of ammonia or nitric acid.”
It would seem that there can be but one explanation of these accurately-ascertained facts. The nitrogenous matter in the manure is not in an available condition. It is in the manure, but the plants can not take it up until it is decomposed and rendered soluble. Dr. Vœlcker analyzed “perfectly fresh horse-dung,” and found that of free ammonia there was not more than one pound in 15 tons! And yet these 15 tons contained nitrogen enough to furnish 140 lbs. of ammonia.
“But,” it may be asked, “will not this fresh manure decompose in the soil, and furnish ammonia?” In light, sandy soil, I presume it will do so to a considerable extent. We know that clay mixed with manure retards fermentation, but sand mixed with manure accelerates fermentation. This, at any rate, is the case when sand is added in small quantities to a heap of fermenting manure. But I do not suppose it would have the same effect when a small quantity of manure is mixed with a large amount of sand, as is the case when manure is applied to land, and plowed under. At any rate, practical farmers, with almost entire unanimity, think well-rotted manure is better for sandy land than fresh manure.
As to how rapidly, or rather how slowly, manure decomposes in a rather heavy loamy soil, the above experiments of Mr. Lawes afford very conclusive, but at the same time very discouraging evidence. During the 19 years, 3,800 lbs. of nitrogen, and 16,492 lbs. of mineral matter, in the form of farm-yard manure, were applied to an acre of land, and the 19 crops of barley in grain and straw removed only 3,724 lbs. of mineral matter, and 1,064 lbs. of nitrogen. The soil now contains, unless it has drained away, 1,736 lbs. more nitrogen per acre than it did when the experiments commenced. And yet 41 lbs. of nitrogen in an available condition is sufficient to produce a good large crop of barley, and 82 lbs. per acre furnished more than the plants could organize.
“Those are very interesting experiments,” said the Doctor, “and show why it is that our farmers can afford to pay a higher price for nitrogen and phosphoric acid in superphosphate, and other artificial manures, than for the same amount of nitrogen and phosphoric acid in stable-manure.”
We will not discuss this point at present. What I want to ascertain is, whether we can not find some method of making our farm-yard manure more readily available. Piling it up, and letting it ferment, is one method of doing this, though I think other methods will yet be discovered. Possibly it will be found that spreading well-rotted manure on the surface of the land will be one of the most practical and simplest methods of accomplishing this object.