When the land has been duly prepared, the seed is sown. This is done sometimes before the last ploughing, but then the manure should have been ploughed in before ; for, except in planting potatoes, which are not a seed but a bulb, the manure should always be deeper, and not in contact with the seed. When the seed is ploughed in, the furrow should not be above two or three inches deep, and eight or nine wide ; and it is only in par ticular soils that this mode is to be recom mended. The most common method is to sow the seed on the land after the last ploughing, and draw the harrows over to cover it : when the laud has been well ploughed, and especially if the press-drill has followed the plough, the seed will mostly fall in the small furrows made by two adjoining ridges, and rise in regular rows. The various modes of sowing are described under Dram. and SOWING.
The proper season for sowing each kind of grain, the choice of seed, and other particulars, are explained under the name of the different seeds usually sown. As a general rule, it may be observed, that the smaller the seed, the less it must be covered, and clover or grass seed are not usually harrowed in, but only pressed in with the roller.
It has been found by experience, that be sides the general exhaustion of humus(decaying vegetable matter) produced by vegetation, especially by those plants which bear oily or farinaceous seeds, each kind of crop has a specific effect on the soil, so that no care, or manure, can make the same ground produce equal crops, of the same kind of grain, for any length of time without the intervention of other crops. The various important circum stances which bear on this question are noticed under FALLOW, FARM, and ROTATION OF CROPS.
The quantity of arable land in Great Bri tain was roughly estimated some years ago as follows :—England, 10,900,000 acres ; Scot land, 2,500,000 acres ; Wales, 900,000 acres. It was ascertained in 1847 that in Ireland, in that year, about one-fourth of the whole area (= 5,238,675 acres out of 20,808,271) was under crops, one sixth under corn culture, and one eighteenth under pasture and clover: