WHY WHEAT PREFERS A HEAVY SOIL. 223 



the quantity of the alkaline and other compounds present in it, there can 

 be no question, — since not only do we find extraordinary natural luxuri- 

 ance of vegetation where some of these happen to be present in the soil, 

 but we can often greatly increase the apparent productiveness of our 

 fields by spreading such substances over them in sufficient quantity. 



How comes it, then, that the green crops which carry off all these 

 substances in the greatest quantity by very much, should yet least injure 

 the land, — nay, should rather renew and prepare it again for the growth 

 of crops of corn ? 



This is one of the most interesting practical questions which can pre- 

 sent its6lf to us in the existing state of theoretical agriculture ; — but it 

 would carry us away from our more immediate object, were we prema- 

 turely to enter upon the discussion of it in this place. It will hereafter 

 demand our especial attention, when we shall have become familiar 

 with the nature and origin of soils. 



I may be permitted, however, to draw your attention here for a mo- 

 ment — as neither out of place, nor uninteresting, for many reasons, — to 

 an opinion expressed by Liebig on the question why wheat prefers stiff 

 and clayey soils. " Again," he says, "how does it happen that wheat 

 does not flourish in a sandy soil, and that a calcareous soil is also un- 

 suitable for its growth, unless it be mixed with a considerable quantity 

 of clay? It is because these soils do not contain alkalies insufficient 

 quantity, the growth of wheat being arrested by this circumstance, even 

 should all other substances be presented in abundance." — {^Organic 

 Chemistry applied to Agriculture, p. 151,] 



Without dwelling on the fact that excellent crops of wheat are reaped 

 in some parts of our island from sandy and calcareous* soils-:- what kind 

 of crops, we may ask, can be reared with success on the lighter soils to 

 which wheat seems least adapted ? The turnip rejoices in light land, 

 and the potato not unfrequently attains the greatest perfection on a sandy 

 soil. Yet ten tons of potato roots, or twenty of turnip bulbs, — exclu- 

 sive of the tops — contain nearly ten times as much of the two alkalies, 

 potash and soda, as fifty bushels of wheat with its straw included. f 

 What ground is there, then, for the explanation given by Liebig — of the 

 peculiar qualities of the so-called wheat lands ? We might with far 

 greater show of reason assume the converse of his proposition, and infer 

 that wheat does not prefer sandy soils, because they are too rich in alkali! 

 It is singular, and would almost seem to strengthen this converse propo- 

 sition, that beans, peas, and vetches, which are so often resorted to as a 

 good preparative for wheat, contain also a much larger quantity of alkali 

 than the latter grain. Thus the grain and straw together of twenty-six 

 bushels of beans contain 71 lbs., of twenty bushels of peas 26 lbs., and 

 of twenty bushels of vetches 74 lbs. of potash and soda taken together. 



As I have already stated, however, we are not yet prepared for dis- 

 cussing this very curious and interesting question. 



* On the thin chalk soils of the Yorltshire Wolds a crop of wheat is taken every four or 

 five years, yielding an average of 24 or 25 bushels. The rotation is turnips, barley, clover or 

 beans, wheat. 



t According to the analyses of Sprengel given in the previous pages, ten tons of potatoes 

 contain 143 lbs. of alkalies, twenty tons of turnips 154 lbs., and fifty bushels of wheat wRh 

 its straw only 16 lbs. 



