Factors for calculating compounds from manurial ingredients
| Table II. Results of first eight years | 562 | ||
| Table III. Results of subsequent forty years | 562 | ||
| Tablel IV. Wheat grown continuously with farmyard manure (14 tons per annum) | 564 | ||
| Table V. Wheat grown continuously with artificial manures | 565 | ||
| Table VI. Experiments on the growth of barley, forty years, 1852–91 | 566 | ||
| Table VIII. Experiments on the growth of oats, 1869–78 | 567 | ||
| Table IX. Experiments on mangel-wurzel | 568, 569 | ||
| Table X. Experiments with different manures on permanent meadow-land, thirty-six years, 1856–91 | 570 | ||
| Table XI. Experiments on the growth of potatoes—average for five seasons, 1876–80 | 571 | ||
| Table XII. Experiments on growth of potatoes (continued)—average for twelve seasons, 1881–92 | 572 | ||
| _______________ | |||
| Index | 573 | ||
PART I.
HISTORICAL INTRODUCTION
MANURES AND THE PRINCIPLES OF MANURING.
HISTORICAL INTRODUCTION.
Agricultural Chemistry, like most branches of natural science, may be said to be entirely of modern growth. While it is true we have many old speculations on the subject, they can scarcely be said to possess much scientific value. The great questions which had first to be solved by the agricultural chemist were—What is the food of plants? and—What is the source of that food? The second of these two questions more easily admitted of answer than the first. The source of plant-food could only be the atmosphere or the soil. As the composition of the atmosphere, however, was not discovered till the close of last century, and the chemistry of the soil is a question which is still requiring much work ere we shall be in possession of anything like a full knowledge of it, it will be at once obvious that the very fundamental conditions for a solution of the question were awanting. The beginning, then, of a true scientific agricultural chemistry may be said to date from the brilliant discoveries associated with the names of Priestley, Scheele, Lavoisier, Cavendish, and Black—that is, towards the close of last century.
Early Theories on Source of Plant-food.
While this is so, and while we must regard the early attempts made towards solving this question as being, for the most part, of little scientific value, it is not without interest, from the historical point of view, to glance briefly at some of these old interesting speculations.
The Aristotelian doctrine, regarding the possibility of dividing matter into the so-called four primary elements, fire, air, earth, and water, which obtained in one form or another till the birth of modern chemistry, had naturally an important influence on these early theories.
Van Helmont's Theory.
Among the earliest and most important attempts made to solve the problem of plant-growth was that by Jean Baptiste Van Helmont, one of the best known of the alchemists, who flourished about the beginning of the seventeenth century. Van Helmont believed that he had proved by a conclusive experiment that all the products of vegetables were capable of being generated from water. The details of this classical experiment were as follows:—
"He took a given weight of dry soil—200 lb.—and into this soil he planted a willow-tree that weighed 5 lb., and he watered this carefully from time to time with pure rain-water, taking care to prevent any dust or dirt falling on to the earth in which the plant grew. He allowed this to go on growing for five years, and at the end of that period, thinking his experiment had been conducted sufficiently long, he pulled up his tree by the roots, shook all the earth off, dried the earth again, weighed the earth and weighed the plant. He found that the plant now weighed 169 lb. 3 ounces, whereas the weight of the soil remained very nearly what it was—about 200 lb. It had only lost 2 ounces in weight."[1]
The
