Jethro Tull, of Shalborne, in Berkshire, inventor of the "hoe-plough" and the turnip drill, was an experimenter and a man of very strong opinions who believed that others should follow his lead. He said that all his advice was based on "full experience" and had been "most infallibly proved". Unfortunately, he seems early in his career to have come to the conclusion that all plants feed on very fine particles of soil and on that alone, and all his subsequent experiments were made to prove that theory.
Tull, perhaps because of his very strong opinions, seems to have had much trouble with his "plough servants", and this led him to decide to plant all his farm with sainfoin ("St. Foin", he calls it). But he soon found that it was very difficult to get enough seed to sow seven bushels to each acre, which was the usual. " Whereupon I began to consider whether so great a quantity of seed was absolutely necessary; and whether the greatest part of the seed sown did not commonly miscarry, either by its badness, or from being buried too deep, or else lying on the ground uncovered." He experimented with several fields of sainfoin and found that he got only about one plant per square foot although he had sown seeds enough for 140 plants for each square foot. So after that he employed " people to make channels, and sow a very small proportion therein and cover it exactly. This way succeeded to my desire, and was in seed and labour but a fourth part of the expense of the common way, and yet the ground of seed was better planted." Thus, as it were by chance, began row planting, which has been described as the greatest advance in agriculture up to that time. It made possible cleaner, better worked fields, and the spaced out plants, developing better, gave much heavier yields.
The hoe-plough
His view was that " Hoeing once well done is twice done ": that is as true today as two hundred and fifty years ago. Tull's hoe was like a plough without a mould-board; and he also used a three-pronged plough almost identical with that still used in some parts for ploughing out potatoes, though Tull used it only for hoeing. Going through his crops repeatedly with horse implements Tull not only got a good tilth, but also kept weeds down. He achieved this more cheaply than his neighbours who up to then had always employed handweeders who unavoidably trod on a lot of the closer-growing crops and did not always pick so clean because their work was not so easy to see.
His book, "Horse-hoeing Husbandry" (1731), begins with a chapter on roots, which he says are of two kinds only, "horizontal roots" and "tap roots", some horizontal roots, he said, growing three times the height of the plant in a season. He goes on:
"All the nutriment (or pabulum) which guts receive for the use of the animal is brought to them; but roots must search out and fetch themselves all the pabulum to the plant, therefore the greater quantity of roots in length of number is necessary to the plant than guts to the animal. All roots are as the intestines of animals and have their mouths or lacteal vessels opening on their outer spongy superfices. . . . When roots are in tilled soil the greater pressure is made against them by the earth which continually subsides and presses their food closer and closer even into their mouths, until it becomes so hard and close that the weak sorts of roots cannot penetrate .any farther into it unless reopened by new tillage which is called hoeing."
That gives the gist of Tull's teaching. In the next chapter of his book he set out to explain the "pasture" of plants, by "which he says he means "the interstices or pores or internal superfices" of the soil, which "never having been mentioned or described before by any other that I know of, I am at a loss to describe it by anything else". This "pasture" can be both natural and artificial. The artificial is that which is brought about by tillage, from which there must arise "some new superfices of the broken parts which never has been opened before". His ideal was a soil broken up as fine as dust, because the finer it was the easier the plants could feed on it. By constant tillage and without manuring he grew successively heavier crops of wheat in the same fields for thirteen years.
Manure he considered not only unnecessary but a spoiler of crops. "Dung not only spoils the fine flavour of these our eatables, but inquinates good liquor. The dunged vineyards in Languedoc produce nauseous wine." His view was that deep and proper tillage "can supply the use of dung''
Turnip drill
The cleverness and ingenuity of Tull is illustrated by the drill that he invented for sowing turneps, as he called them. He meant common turnips, the Swedish turnip not then being known here. His drill had eleven shares and would sow three different kinds of seed at a time without mixing them: barley seven inches apart and four inches deep, clover seed three inches above the barley, and between every two of these rows at half-an-inch deep a row of sainfoin, of which he was a great advocate. He knew the value of its deep roots and how such plants would stand drought.
His turnip drill was designed not only to sow seed but to outwit the fly, for it could sow half the seed four inches deep and half, half-an-inch deep. If rain fell immediately after the sowing the top seed came up. If there was drought, it did not matter because the lower seed was sure to come up. Moreover, he mixed old and new seed in his drill so that "it came up at four times, giving it so many chances of escaping the fly''. How he came to invent the drill is interesting. As a youth he was fond of playing the organ, and learnt how one
was made. Later, when he was farming and his men disappointed him again, failing to sow his sainfoin seeds as exactly in the furrows as he wanted them, he sacked his men, " resolving to quit .... unless I could contrive an engine to plant .... more faithfully than such hands would do. To that purpose I examined and compared all the mechanical ideas that ever had entered my imagination, and at last pitched upon a groove, tongue, and spring in the sound-board of the organ. With these a little altered, and some parts of two other instruments as foreign to the field as the organ is added to them, I composed my machine."
His analogies between plant and animal feeding are ingenious. In one place he places "nitre" in a list of what is agreed "to contribute in some manner to the increase of plants", and goes on to say that "nitre is useful to divide and prepare the food and may be said to nourish vegetables in much the same manner as my knife nourishes me by cutting and dividing my meat". He believed that dew did good to plants not only because it moistened them but because "the sulphur, which is found in the sediment of the dew, may be the chief ingredient of the cement of the earth, sulphur being very glutinous, as nitre is dissolvent''. By' 'the cement of the earth'' what can Tull have meant but that which we now call humus; and was not his "nitre" the nitrogen of the atmosphere?