THE FARMER'S MAGAZINE. 



513 



straw, takes from the laud the following quantities of 

 the several ingredients ; 



Grain. Straw. Total, 



Iba. 

 Silica 

 Potash 

 Phosphoric acid 



Lime 



Mafjuesia ' 4.25 



Sulphuric acid } 0.112 



Soda 1.35 



Peroxide of iron, aud loss ! 0.2S 

 Chloride of BOiiiuoj | 0.042 



I 34.904 209.97 244.874 

 Of the 245 lbs. of mineral matters in a crop of wheat, 

 210 lbs. are in the straw ; so that by returning the straw 

 to the land, in the form of manure — not necessarily 

 every year, but say every third or fourth year— we 

 have only to demand of the soil a perpetual supply of 

 thirty-five pounds of minerals, that is, one pound per 

 bushel, sent off the farm in the corn soldj to which 

 must be added the waste of a portion of these substances 

 during the conversion of the straw into dung. What 

 stock of these particular minerals, then, have we in a 

 common loam! The following actual quantities are 

 calculated from an analysis of a loam containing eighty 

 per cent, of silica ; and I will take the depth of staple 

 at ten inches, as calculated in my experiments, the 

 weight of one acre being about 3,267,000 lbs., or 

 1,458 tons: 



Enough for 

 2,646,666 lbs. 22,144,444 crops. 

 26,024 „ 2.484 „ 



12,414 „ 775 „ 



42,470 „ 35,388 „ 



36.590 „ 8,555 „ 



2,940 „ 26,222 „ 



49.004 „ 37.777 .. 



111,077 „ 396,666 „ 



" trace." abundance. 



Silica 



Potash 



Phosphoric acid . . . . 



Lime 



Magnesia 



Sulphuric acid 



Soda 



Peroxide of iron, &c. 

 Chloride of sodium . . 



Were we to take away both grain and straw, without any 

 return whatever, there would be sulphuric acid enough 

 for 366 crops, phosphoric acid for 451 crops, potash 

 for 725 crops, lime for 3,033 crops, and the other 

 minerals in a still larger profusion. So that the only 

 substances that a long-continued series of crops could 

 sensibly reduce are just those which can he readily sup- 

 plied again in a dressing of ordinary artificial manure. 

 But I advocate the successive growth of only a limited 

 series of wheat-crops upon the various fields of a farm in 

 their turn, the straw being restored to each field in the 

 year occupied by the leguminous or green crop which fol- 

 lows ; the foregoing table showing that, with such a rota- 

 tion, a common loam is practically inexhaustibleof mineral 

 constituents. And therefore no landowner or vigilant 

 agent need look grave when tenants ask permission to 

 adopt Lois-Weedon wheat-growing on such land. It 

 is supposed that the various mineral substances exist in 

 the soil in a crude condition unfitted for the use of 

 plants, only a small proportion being directly available 

 as food for the roots. And this stock of liberated or 

 active mineral matter is maintained or increased by ex- 

 posing the crude substance to the solvents of the atmo- 

 sphere; which is principally effected by drainage and 



mechanical cultivation. The action of atmospheric 

 agencies upon the constituents of the soil is too lengthy 

 a subject for notice at this time ; and I need only mention 

 one fact — that the slow and continuous action of rain- 

 water containing carbonic-acid is found to dissolve sub- 

 stances which resist the most biting corrosive acid or the 

 most caustic alkali. The idea that roots take up nou- 

 rishment only in solution is giving way, however, to a 

 nev opinion — that roots are enabled by simie process of 

 vital chemistry to feed upon perfectly-insoluble particles 

 of aliment with the surface of which they are in contact. 

 The power with which earth seizes and retains plant- 

 food in defiance of all the natural solvents, has led Liebig 

 to this conclusion : just the theory, you will remember, 

 of our profound agricultural discoverer, old Jethro Tull, 

 on which he built his system of frequent intercultural 

 tillage. How much tillnge, then, will provide and pre- 

 pare a sufficiency of the minerals for the wants of the 

 crop while growing? Well, the amount of forking and 

 horse-hoing bestowed at Lois-Weedon has been found 

 amply sufficient for a long series of the heaviest crops ; 

 my own ploughing, subsoiling, and scarifying have been 

 found sufficient for several fair crops ; and the cultiva- 

 tion practised in other cases has also been adequate for 

 the purpose. On Mr. Lawes' heavy loam at Koth- 

 amsted, one scarifying and cleaning, and one ploughing 

 five or six inches deep, followed by a few harrowings, 

 are found enough for the production of a yield of six- 

 teen bushels per acre, for any number of years in suc- 

 cession. And the corroborative evidence from the steam- 

 farming of Mr. Smith, of Woolston, and numerous other 

 instances, shows that, on any soil not too thin and light, 

 minerals enough for a long succession of heavy corn- 

 crops can be prepared by a very moderate and prac- 

 ticable amount of tillage operations. Besides this 

 terrestrial nutriment, however, plants require " aerial," 

 or organic, food : indeed, all but a fractional portion of 

 the substance of our crops is elaborated and built up 

 out of such unstable materials as gas and water. I 

 cannot now branch off into an elucidation of the ab- 

 sorptive functions of leaves and green stems, and the 

 necessity for having a store of organic matter within the 

 soil, as well as floating in the air above. The only 

 element which it may be feared would fall short in our 

 successive wheat-growing is the expensive nitrogen. 

 No chemist or vegetable-physiologist ventures to say 

 that the wheat-flag and succulent stalk are utterly unable 

 to absorb this element out of the atmosphere in the form 

 of volatile ammonia or other compounds ; only the supply 

 in this manner is thought to be comparatively little. 

 Doubts also exist as to the quantity of nitrogen brought 

 down to the soil in one year by the rains and dews, 

 which wash it out of the atmosphere in the form of nitric 

 acid and ammonia ; but the most subtle and delicate 

 analyses appear to show that it is a good many pounds' 

 weight per acre short of the amount required by a wheat- 

 crop. How, then, shall it be obtained without manuring ? 

 Well, there is a good stock of nitrogen already in the 

 soil to begin with. According to Mr. Lawes' analysis 

 of the Rothamsted and Lois-Weedon soil, an acre of 

 land ten inches deep'contains 2\ tons of this precious 



