1844.] 



THE AGRICULTURAL GAZETTE. 



841 



red sandstones. The sandstones and the limestones were | the science of agriculture, and expressed his sense of its 

 thus replete with matter ready-formed to he used as food importance. 











for plants. Succeeding to the period of their formation 

 was that of the great vegetable era in which the coal-beds 

 were formed. The effect of the decomposing vegetable 

 matter on the peroxide of iron was remarkable, and 

 worthy of attention. When the plants began to decay, 

 they converted the peroxide into the protoxide, and when 

 this latter was formed, it acted injuriously on vegetation 

 and destroyed it. It was thus, he'.believed, that great bed/? 

 were formed at the present day ; the decaying plants 

 converted the peroxide of iron into the protoxide, and 

 when this ingrpdient was formed it destroyed the remain- 

 ing living plants. The blue clays deposited underneath 

 Peat-beds was a proof of the correctness of this view. 

 The peroxide was, however, easily convertible into the 

 protoxide by exposure to the oxygen of the atmosphere. 

 It was by subsoil-ploughing that the farmer could render 

 available his blue clays for the nutrition of plants. It 

 was thus that Nature came with her great subsoil-plough, 

 the ocean, and threw up on the shores the injurious prot- 

 oxide in the form of a peroxide, as well as effected other 

 important changes. Now the farmer might learn a great 

 lesson from the way in which Nature acted in preparing 

 the constituents of plants. The elements necessary 

 for feeding plants of the present era were in the primi- 

 tive rocks, but they underwent preparation before 

 they were administered as food. If a child became 

 ricketty for the want of phosphate of limejin its food, no 

 one would think of feeding it with crystals of Apatite 

 phosphate of lime ; or if a lady became bilious for want 

 of soda in her system, what doctor would administer 

 lumps of felspar ? It was the same with plants : it is of 

 no use to administer the constituents they require in a 

 form they cannot digest. In the lirst place, the farmer 

 must take care that he has food for his plants in the soil ; 

 and in the second place he must take care that they get 

 at the food. Now, most soils contained many of the 

 constituents required by plants in the rocks of which the 

 ^arthwas composed ; but then these rocks required pre- 

 paring ; and how was this to be done ? It was by plough- 

 ing and by subsoil-ploughing. Practice had suggested 

 this, and science pronounced that it could not be dis- 

 pensed with. By ploughing, the soil was reduced to 

 powder, ar.d the potash, the soda, and the lime had 

 access to the carbonic acid and oxygen and water of the 

 atmosphere, by which the important changes before re- 

 ferred to were produced. By ploughing, also, the soil 

 became absorbent. It took into its very interior, where 

 the roots of plants were seeking their food, the carbonic 

 acid, the ammonia, and the water, which were the prin- 

 cipal organic constituents of plants. In such a soil and 

 with such agents did God grow the first forests of the 

 world, and in such a manner must man act in order to 

 grow the plants which he needs. The lecturer then 



e 

 was 



went into calculations to show the enormous quan- 

 tities of silicate of potash and soda contained in 

 felspathic rocks, clay, slate, and loam, to show 

 that where these rocks existed there could never be 

 a deficiency of these agents. There was, however, a 

 danger of ploughing up such soils too much ; silicate 

 of potash entered into the composition of the stems ; 

 it was phosphate of lime that entered into the seeds as 

 well as the stems. Now, if the stems of plants were 

 made to grow too luxuriously, by the aid of the silicate of 

 potash, they would arrest the phosphate of lime going to 

 the seed, and thus would do injury. The phosphate of 

 lime existing in much smaller quantities in most soils, 

 needed more frequently artificially renewing than the si- 

 licates. These were added in the form of guano, bone- 

 dust, && In conclusion, he would add a few words on 

 draining. "When water was allowed to accumulate in a 

 soil, it prevented the access of air, and thus prevented 

 the action of the oxygen and carbonic acid on the ingre- 

 dients of the soil. Water also dissolves up and carries 

 off the most important constituents of a toil, and thus 

 renders the land poor. Plants also require a certain 

 temperat ue, and water, by its great absorption of heat 

 during the process of vaporisation which was constantly 

 going on, was a constant means of reducing 

 the temperature of the soil. As a proof of the 

 influence of the temperature of the soil on the 

 development of plants, he pointed out tliat in low 

 and heavy, and undrained districts, the harvest 

 was always more backward than in high districts 

 with a natural drainage, although the average tempera- 

 ture of the former districts was much higher. Whole 

 counties in this country were badly drained; and he gave 

 Cheshire as an illustration. This county was so badly 

 drained, that it was said it was unfit for sheep to live in ; 

 he would only add, if it was unfit for sheep it certainly 

 Was unfit for man. This was an important considera- 

 tion, that draining, which provided for a larger supply of 

 food for man, also provided for the existence of man to 

 consume the food. He illustrated the importance of 

 drainage by relating a fact which had been communicated 

 to him by Professor Liebig. Near Giessen is a prison 

 from which dead bodies are supplied to the University for 

 anatomical purposes. Atone time it was very unhealthy, 

 and a large number of deaths occurred, but the public 

 authorities had lately had the district drained in which it 

 was situated, and 6ince that period the deaths in the 

 place had been so few, that the University was now 

 obliged to send to other places to Supply its anatomical 

 wants. 



The M.ARauis of Downshire hoped that the Lecture 



which had just been delivered would be published, and 



Iproposed a role of thanks to Dr. Playfair. — Lord 



Spknckr seconded the motion, and made some remarks 



on the geological view which the Lecturer had taken of 



The Chairman- stated that the Lecture would be 

 published in the Journal of the Societv, and proposed a 

 vote of thanks to the Governors of the Royal Institution 

 for their kindness in allowing the use of their commo- 

 dious theatre for the Lecture of the Society. 



_, _ DR - PLAYFAIR'S SECOND LECTURE. 



I he Lecturer commenced by stating, that in his last 

 Lecture he had endeavoured to demonstrate that th 

 sequence of events from the first dawn of creation .._ 

 calculated to elucidate the theory of the practice of agri- 

 culture. It was seen how carefully Nature had prepared 

 her soils for cultivation, long before man had devoted 

 himself to her service. He had showed how the ocean 

 had acted as a great plough and subsoil-plough, and 

 ameliorated the noxious ingredients in the rocks, and 

 fitted those which were fertile for the purposes of vege- 

 tation. How curiouslv she locked up in the soil 

 those treasures of fertility, and the manner in which 

 she presented the key to the industry of man, and 

 showed him, by her own example, wisely reduced in 

 energy from the past, when she herself had to clothe 

 her own lands with vegetation, without man's aid. 

 Still, though she reduced in intensity the causes for- 

 merly in operation, she preserved them in store for 

 action, if that became necessary; and instances were seen 

 in the operations of subsoil-ploughing and draining, in 

 which she proved no niggard, when these causes were 

 called into activity. We followed Nature also in those 

 high and bleak regions of calcareous and cretaceous rocks, 

 and then of the old red sandstone, in which she compen- 

 sated for their elevation by an admirable system of 

 drainage, either by causing numerous clefts or a porous 

 nature of materials, so that the water might be quickly 

 draughted away, and not by its evaporation render the 

 soil cold ; and, in this manner, how she pointed out to 

 the farmer how best to improve the climate of his own 

 district, how to increase as well as hasten the amount of 

 vegetation, and the best way of making the capability of 

 the soil available, and of obtaining the quickest return 

 for the labour which was expended in its cultivation. 

 In the present Lecture he should endeavour to apply the 

 principles deduced from the observation of Nature, on a 

 large scale, to the practice of the farmer, on a small one ; 

 and he believed that every one who neglected the study 

 of these principles, would ever after have much reason 

 to regret that he had not consulted the wishes and be- 

 come acquainted with the elevated character of his great 

 mistress. In the last Lecture, the importance of 

 ploughing and draining had been insisted on; and this 

 involved the explanation of fallow — the exposure of the 

 constituents of the soil to the atmosphere. But 

 although a soil is exhausted, for instance, of sili- 

 cate of potash, so that Wheat would not grow, it 

 did not follow necessarily that no other crop would 

 grow, as there might still be plants that would 

 grow with the remaining constituents of the soil. This 

 subject was one of importance, as, if there were such 

 crops, it would obviously present the necessity of a 

 naked fallow. Professor Low, in his Agriculture, had 

 recommended that soils be ploughed six or eight times ; 

 and this was a great waste of time and money, if nothing 

 else could be grown in the interim. But in Scotland, in 

 many parts of England, and in Jersey, such a system 

 was now entirely dispensed with, and the theory of such 

 a practice is easily understood by referring to what has 

 recently been ascertained with respect to the composi- 

 tion of the mineral ingredimts of plants. In the last 

 Lecture a table was exhibited showing the principal mi- 

 neral ingredients of plants, and although all plants con- 

 tained these, they existed in very variable proportions, 

 as the following table would show ; and Liebig had even 

 divided plants into classes, according to their mineral 

 constituents : — 



sture, or in other words, to the growth of lime plants. 

 Clay, slate, and grauwacke are degraded granite, but de- 

 ficient in lime and phosphates ; for animals had not yet 

 been formed, and their great characteristic was the 

 possession of potash ; and two po'.ash plants, Oats, 

 and Turnips, were most frequently cultivated on these 

 soils, both of them requiring little of the phosphates and 

 little of lime; on the sandstones, which were much richer 

 in lime and phosphates, but still possessing potash, so 

 that potash plants, and i.i addition, Wheat, Barley, and 

 Clover, are grown on these soils. Above the sand- 

 stones we come to rocks abounding with animal and 

 vegetable remains, and containing little potash; these 

 rocks are not adapted for Wheat, Barley, Oats, or Tur- 

 nips, and the lime-plants forming pas'tures are mostly 

 grown. On the coal measures vegetation is poor, arising 

 from the enormous exhaustion of the soil, produced by 

 the plants forming the coal-beds ; the clays, however, 

 contained silicates and iron, and with care were cultivated 

 so as to produce various crops. On the magnesian lime- 

 stone plants were grown which required magnesia, and 

 Potatoes, Wheat, and Barley flourished on these soils. 

 After this we come to the new red sandstone, a soil com- 

 posed of the detritus of former rocks, and of 

 supporting potash, soda, and silica plants. The calca- 

 reous soils of the lia*, the oolite, and the chalk yield 

 lime-plants, Means, I' .Clover, and Barley. In 'exa- 

 mining the various kinds of rotations, it would be found 

 that they were precisely such as were adapted to the 

 soils in which they took place. Thus the Norfolk course 

 begins with Turnips well manured, succeeded by a corn 

 crop, followed by artificial Grasses, and concluded by 

 another crop of corn ; and this took place on most of the 

 inferior clays of England. The manure yielded phosphates, 

 but neither these nor the silica were taken up by 

 the Turnips, and the soil thus became prepared f the 

 growth of the corn, as the only thing of importance re- 

 moved from the soil by the Turnips was the potash ; and, 

 what was important, potash uncombined with silica. If 

 sheep upon the Turnips, they return to the soil the potash 

 contained in the Turnips, and also of phosphates. 

 After the second or corn crop has exhausted the soluble 

 silicates and phosphates, a green crop is then grown, 

 and this takes up the lime. By the time the lime is 

 taken up by this crop, the action of the air upon the 

 soil has liberated a further quantity of phosphates and 

 silicates sufficient to grow for a fourth crop corn, which 

 is often Barley, where lime is present, or Oats, or Wheat 

 where it is deficient. Where there is magnesia present, 

 as on the magnesian limestone, Potatoes may be substi- 

 tuted with advantage for the green crop, especially as 

 their stems return to the soil the silicates. The curious 

 rotation of the lower lias, consisting of Wheat, Beans, 

 fallow, Oats, and Potatoes, would in the same way be 

 found adapted to the particular composition and charac- 

 ters of the soil on which it was practised. Enough had 

 probably been said to show the farmer that rotation 



The soil 





Salts of 



Salts Of 





Potash 



' Lime and 







and Soda. 



Magrjesia. 



Silica Plant?. 







Oat-straw, with seeds . 



34.00 



4.00 



Wheat- straw .... 



22.00 



7.20 



Barley- straw, with seeds 



19.00 



25. 70 



Rye -straw .... 



18.65 



16.52 



Lime Plants. 







Tobacco .... 



24 34 



67.44 



Pea straw .... 



2/.82 



63.74 



Potato, herb .... 



4.20 



5940 



Meadow Clover 



39.20 



56.00 



Potash Plants. 







Maize-straw .... 



71.00 



6.50 



Turnips 



81.60 



18.40 



Beet-root .... 



88.00 



12 00 



Potatoes (tubers) . . 



.85.81 



14.19 



Helianthus tuberoses . 



84 30 



15.70 



Silica. 



62.00 

 61.05 



55.03 

 63.89 



8.30 



7.SI 



36.40 

 4.90 



18.00 



This Table is only an approximation to the truth, and 

 its classification inadmissible, as it was opposed to a beau- 

 tiful law, pointed out by Liebig himself, and confirmed by 

 the experiments of Will and Fresenius, which was that 

 certain bases may replace each other, according to the 

 law of equivalents. Thus, soda may be substituted 

 for potash, and vice versa; lime for magnesia, and so 

 on ; but it did not appear that an alkali could be sub- 

 stituted for an earth; still the Table was practically 

 useful. The rotation of crops must depend on the cha- 

 racter of the soil, and this would be seen by observing 

 what kind of plants grew on the rocks mentioned in the 

 last Lecture. On the granite roeks, the soil of which 

 contained abundance of silicate of potash, the farmer 



grew mostly the silica plants, as Wheat, Barley, and 

 Oats, after taking care to manure well with lime or sea- 

 shells, to supply the absent calcareous matter and phos- 

 phates. It is seldom that such soils are devoted to because they are the great generators of the constituents 



was not a means of improving the soil, 

 remained En the same state, as far as the plant wu 

 concerned, and the great advantage of it consisted 

 in the fact that one crop could be grown whilst the 

 soil was preparing for auother. The theory of De 

 Candolle, with regard to plants throwing out excremen- 

 titious matter injurious to themselves and beneficial to 

 other plants, was now generally exploded, and many facts 

 were entirely opposed to it. Thus, in Hungary, there 

 was never a poisonous effect produced on the Wheat 

 crops, although in some districts Wheat had been grown 

 in succession for centuries. A like result to that of ro- 

 tation is produced by many other processes on farms ; 

 take, for instance, burning and paring. By this process 

 injurious organic matter is consumed. Plastic clays are 

 quite changed in their character, not only by having all 

 their constituents brought into contact with the oxygen 

 of the atmosphere, and thus undergo change, but the 

 clay itself acquires another character, it becomes ab- 

 sorbent, and takes up from the atmosphere ammonia, 

 carbonic acid, and watery vapour, as well as afford 

 more ready access to the nutritious substances which 

 may be dissolved in water. Bat in this, you see 

 nothing is destroyed, and the inorganic elements 

 of the soil are only brought more fully into con- 

 tact with the absorbing organs of the plants. Another 

 process of the farm was what was called liming. When 

 the chemist, in his laboratory, wished to dissolve up 

 potash and silica from the soil he was examining, he 

 used lime ; and by this means he rendered soluble that 

 which was insoluble before. Just what the chemist did 

 in his laboratory by the use of lime, the farmer did in 

 his fields ; and this was the use of lime, that it rendered 

 certain important ingredients of the soil more soluble 

 than they were by nature. In this way, lime became 

 a key by which the ingredients in the soil were un- 

 locked ; it did not in itself become an important 

 ingredient in the soil. It may, however, happen 

 that where we add lime, we may not only be using 

 a means for unlocking the ingredients of the soil, 

 but we may also be adding an important constituent of 

 the soil. This was what made lime an important ingre- 

 dient as a top-dressing where Clover and Grasses were 

 to be grown. It would be seen, then, that lime was not 

 used principally as a manure ; it was seldom required as 

 a manure, for a manure added to the composition of 

 the soil; its principal use was as a solvent of other 

 materials. Common salt was sometimes used as a manure, 

 and Liebig supposed that it acted beneficial ; y by 

 combining with sulphate of lime, and a sulphate of soda 

 was produced. If this was the case, it should act most 

 beneficially on the cereals, and on the leguminous plants 



