Slightly exotic crops face an annual risk. Maize, for example, requires more warmth than is generally available in Britain, but now quick-ripening varieties are bred and some is grown as a vegetable for cutting while still soft and sweet. Tomatoes are a chancy crop in the open, even when the young plants are grown under glass; they fail to ripen in years of cool summer. Most of the soft fruits do quite well but commercial fruit-growing shows a preference for sunny climate and long autumns and the 'gardens of England' mostly lie within the area of more than 1,400 hrs of sunshine in the year. Some quality of the climate in fact sets a limit to most crops at some point in Britain, in latitude or altitude, or in local conditions of exposure. By long experience the professional knows the limits of safety; only the amateur can afford to take a chance and pay for it in a bad year.
It is not suggested that climate is the only cause of crop distribution. Relief limits commercial production to flattish lands or to valley floors, and soil too has its effects. One of the most striking features noticeable in the agricultural atlas is the concentration of potatoes on the fen and warp soils of the Wash and Humber, while sugar-beet likes light soils.
But soil itself is partially determined by climate. Though there are many local soils, Britain has only two zonal types, podsols (humid) and brown forest soils (sub-humid). The former dominate in the cold north and the wet west where a heavy excess of winter rain with small evaporation loss leaches out the soluble salts leaving an impoverished grey soil beneath a black layer of raw humus and, under coniferous forest, of resinous pine-needles. In the lowland zone is a less leached brownish soil of generally higher base-status, in a climate which is naturally fitted to deciduous forest. Both soils lose fertility under cultivation; the bases and their soluble salts, lime and potash, which constitute important crop-foods, need constant replenishment, either with artificial fertilizers or farmyard manure or by a sound system of crop rotation, including treading by stock, the ploughing-in of humus, and the introduction of leguminous crops to fix atmospheric nitrogen. It is only because of the limited range of the climate, and therefore of soils that British soil scientists often refer to soils in terms of the parent material, but, given time, the end-product would be a reflexion of the climate. But nearly all British soils have had centuries of management; natural soils are only to be found in uncultivated regions, uncultivated mainly for reasons of geology, for example, sandy heathlands, swampy marshes and blanket bogs. Even in such places the Forestry Commission has found an economic use for barren soils and makes trees grow. Its activities have in the forty years of its existence revolutionized what was formerly waste land. Generally speaking some trees, many of them exotic, will give a commercial yield and the regimented rows of conifers cover about 1½ m. acres of land in Scotland, about ½ m. in Wales and 1¾ m. in England. For reasons of quick financial return conifers are generally preferred and the native oak forests on the claylands and to a less extent beech on the drylands are being replaced. Coppices decline slowly, but still survive to provide local timber for gates, fences and poles and to give cover for the pheasants and foxes that still provide picturesque but uneconomic sport for the countryman. The hedgerow trees, elm, ash, horse chestnut and sycamore, keep their place and give variety and charm to the 'bocage' lands of the English counties and the Welsh marches.