This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Deep tillage is a splendid thing in the cultivation of vegetables; but before the market gardener, who wants to keep clear of the bankruptcy court, listens to the advice of those who would advise the bringing up of the subsoil, let him try small experiments. Let him, above all things, keep his land cropped. Let him remember that good crops and plenty of hoeing are half the battle in cleaning dirty land. Where land is ploughed, and there is enough horse strength, the subsoil grubber can always be made to follow the plough, except in the rush of summer, when the land cleared in the evening should be recropped the next day.
A good and inexpensive subsoil grubber can be made by buying an old iron plough at a sale and simply removing the breast.