“Mr. Lawes found,” continued the Doctor, “that a wheat-plant, from March 19 to June 28, or 101 days, evaporated through its leaves, etc., 45,713 grains of water; while a clover-plant, standing alongside, and in precisely similar condition, evaporated 55,093 grains. The clover was cut June 28, when in full bloom. The wheat-plant was allowed to grow until ripe, Sept. 7. From June 28 to Sept. 7, or 72 days, the wheat-plant evaporated 67,814 grains.”
“One moment,” said the Deacon; “as I understand, the clover-plant evaporated more water than the wheat-plant, until the 28th of June, but that during the next 71 days, the wheat-plant evaporated more water than it had during the previous 101 days.”
“Yes,” said I, “and if these facts prove nothing else, they at least show that there is a great difference between wheat and clover. I was at Rothamsted when these experiments were made. During the first nine days of the experiment, the clover-plant evaporated 399.6 grains of water; while the wheat-plant, standing alongside, evaporated only 128.7 grains. In other words, the clover-plant evaporated three times as much water as the wheat-plant. During the next 31 days, the wheat-plant evaporated 1,267.8 grains, and the clover-plant 1,643.0 grains; but during the next 27 days, from April 28 to May 25, the wheat-plant evaporated 162.4 grains of water per day, while the clover-plant only evaporated 109.2 grains per day. During the next 34 days, from May 25 to June 28, the wheat-plant evaporated 1,177.4 grains per day, and the clover-plant 1,473.5 grains per day.”
“In June,” said the Deacon, “the clover evaporates ten times as much water per day as it did in May. How much water would an acre of clover evaporate?”
“Let Charley figure it out,” said the Doctor. “Suppose each plant occupies 10 square inches of land; there are 6,272,640 square inches in an acre, and, consequently, there would be 627,264 clover-plants on an acre. Each plant evaporated 1,473.5 grains per day, and there are 7,000 grains in a pound.”
Charley made the calculation, and found that an acre of clover, from May 25 to June 28, evaporated 528,598 lbs. of water, or 15,547 lbs. per day.
A much more accurate way of ascertaining how much water an acre of clover evaporates is afforded us by these experiments. After the plants were cut, they were weighed and analyzed; and it being known exactly how much water each plant had given off during its growth, we have all the facts necessary to tell us just how much a crop of a given weight would evaporate. In brief, it was found that for each pound of dry substance in the wheat-plant, 247.4 lbs. of water had been evaporated; and for each pound in the clover-plant, 269.1 lbs.
An acre of wheat of 15 bushels per acre of grain, and an equal weight of straw, would exhale during the spring and summer 177¾ tons of water, or calculated on 172 days, the duration of the experiment, 2,055 lbs. per day.
An acre of clover that would make two tons of hay, would pass off through its leaves, in 101 days, 430 tons of water, or 8,600 lbs. per day—more than four times as much as the wheat.
These figures show that, from an agricultural point of view, there is a great difference between, wheat and clover; and yet I think the figures do not show the whole of the difference. The clover was cut just at the time when the wheat-plant was entering on its period of most rapid growth and exhalation, and, consequently, the figures given above probably exaggerate the amount of water given off by the wheat during the early part of the season. It is, at any rate, quite clear, and this is all I want to show, that an acre of good clover exhales a much larger amount of water from spring to hay-harvest than an acre of wheat.