“Barnyard-manure,” said the Doctor, “is altogether too ‘lasting.’ Here we have had 56 tons of manure on an acre of land in four years, and yet an acre dressed with 500 lbs. of guano produces just as good a crop. The manure contains far more plant-food, of all kinds, than the guano, but it is so ‘lasting’ that it does not do half as much good as its composition would lead us to expect. Its ‘lasting’ properties are a decided objection, rather than an advantage. If we could make it less lasting—in other words, if we could make it act quicker, it would produce a greater effect, and possess a greater value. In proportion to its constituents, the barn-yard manure is far cheaper than the guano, but it has a less beneficial effect, because these constituents are not more completely decomposed and rendered available.”
“That,” said I, “opens up a very important question. We have more real value in manure than most of us are as yet able to bring out and turn to good account. The sandy-land farmer has an advantage over the clay-land farmer in this respect. The latter has a naturally richer soil, but it costs him more to work it, and manure does not act so rapidly. The clay-land farmer should use his best endeavors to decompose his manure.”
“Yes,” said the Doctor, “and, like John Johnston, he will probably find it to his advantage to use it largely as a top-dressing on the surface. Exposing manure to the atmosphere, spread out on the land for several months, and harrowing it occasionally, will do much to render its constituents available. But let us return to Mr. Lawes’ wonderful experiments.”
“On eight plots,” said I, “300 lbs. of ammonia-salts were used without any other manures, and the average yield on these eight plots was nearly 26 bushels per acre, or an average increase of 9 bushels per acre. The same amount of ammonia-salts, with the addition of superphosphate of lime, gave an increase of 13 bushels per acre. 400 lbs. ammonia salts, with superphosphate of lime, gave an increase of nearly 16 bushels per acre, or three bushels per acre more than where 14 tons of barn-yard manure had been used four years in succession.
“I hope, after this, the Deacon will forgive me for dwelling on the value of available nitrogen or ammonia as a manure for wheat.”
“I see,” said the Deacon, “that ground rice was used this year for manure; and in 1845, tapioca was also used as a manure. The Connecticut Tobacco growers a few years since used corn-meal for manure, and you thought it a great waste of good food.”
I think so still. But we will not discuss the matter now. Mr. Lawes wanted to ascertain whether carbonaceous matter was needed by the growing wheat-plants, or whether they could get all they needed from the soil and the atmosphere. The enormous quantities of carbonaceous matter supplied by the barn-yard manure, it is quite evident, are of little value as a manure for wheat. And the rice seems to have done very little more good than we should expect from the 22 lbs. of nitrogen which it contained. The large quantity of carbonaceous matter evidently did little good. Available carbonaceous matter, such as starch, sugar, and oil, was intended as food for man and beast—not as food for wheat or tobacco.
The following table gives the results of the experiments the fifth year, 1847-8.