658 



FARMERS' REGISTER, 



No. 11 



ble living vegetable matter; and I have since i 

 heard that a great improvement took place. 



Many obscure causes have been relerred to for 

 the purpose of explaining the etiects of paring 

 and burning ; but I believe they may be relijrred 

 entirely to the diminution of the coherence and 

 tenacity of clays, and to the destruction of inert 

 and useless vegetable matter, and its conversion 

 into a manure. 



Dr. Darwin, in his Phytologia, has supposed 

 that clay during torrefaction may absorb some nu- 

 tritive principles from the atmosphere that after- 

 wards may be supplied to plants ; but the earths 

 are pure metallic oxides, saturated with oxygen ; 

 and the tendency of burning is to expel any other 

 volatile principles that they may contain in com- 

 bination. If the oxide of iron in soils is not satu- 

 rated with oxygen, torrefaction tends to produce 

 its further union with this principle ; and hence in 

 burning the color of clays changes to red. The 

 oxide of iron containing" its full proportion of oxy- 

 gen has less attraction for acids than the other 

 oxide, and is consequently less likely to be dissolved 

 bv any fluid acid in the soil ; and it appears in 

 this state to act in the same manner as the earths. 

 A very ingenious author, whom I quoted at the 

 end of the last lecture, supposes that the oxide of 

 iron when combined with carbonic acid is poison- 

 ous to plants, and that one use of torrefaction is 

 to expel the carbonic acid from it ; but the car- 

 bonate of iron is not soluble in water, and is a very 

 inert substance ; and I have raised a luxuriant 

 crop of cresses in a soil composed of one-fifih car- 

 bonate of iron, and four-fifths carbonate of lime. 

 Carbonate of iron abounds in some of the most 

 fertile soils in England, particularly the red hop 

 soil. And there is no theoretical ground for sup- 

 posing that carbonic acid, which is an essential 

 food of plants, should in any of itt5 combinations 

 be poisonous to them ; and it is known that lime 

 and magnesia are both noxious to vegetation un- 

 less combined with this principle. 



All soils thai contain too much dead veoetable 

 fibre, and which consequently lose from one-third to 

 one-half of their weight by incineration, and all such 

 as contain their earthy constituents in an impalpa- 

 ble state of division, i. e. the stiff clays and maris, 

 are improved by burning ; but in coarse sands, 

 or rich soils containing a just mixture of the 

 earths, and in all cases in which the texture is al- 

 ready sufficiently loose, or the organisable matter 

 sufficiently soluble, the process of torrefaction can- 

 not be useful. 



All poor siliceous sands must be injured by it ; 

 and here practice is found to accord with theory. 

 Mr. Young, in his Essay on Manures, states, 

 " that he found burning injure sand ;" and the 

 operation is never performed by good agricultu- 

 rists upon siliceous sandy soils, after they have 

 once been brought into cultivation. 



An intelligent farmer in Mount's Bay told me 

 that he had pared and burned a small field several 

 years ago, which he had not been able to bring 

 again into good condition. 1 examined the spot ; 

 the grass was very poor and scanty, and the soil 

 an arid siliceous sand. 



Irrigation, or watering land, is a practice 

 which, at first view, appears the reverse of torre- 

 faction ; and in general, in nature, the operation 

 of water is to bring earthy substances into an ex- 

 treme stale of division. But in the artificial wa- 



tering of meadows, the beneficial effects depend 

 upon many different causes, — some chemical, 

 some mechanical. 



Water is absolutely essential to vegetation ; and 

 when land has been covered by water in the win- 

 ter, or in the beginning of spring, the moisture 

 that has penetrated deep into the soil, and even 

 the sub-soil, becomes a source of nourishment lo' 

 the roots of the plant in the summer, and prevents 

 those bad effects that olien happen in lands in 

 their natural state, from a long continuance of dry 

 weather. 



When the water used in irrigation has flowed 

 over a calcareous country, it is generally found 

 impregnated with carbonate of lime ; and in this 

 state it tends, in many instances, to ameliorate the 

 soil.* 



Common river-water, also, generally contains a 

 certain portion of organisable matter, which is much 

 greater after rains than at other times ; and which 

 exists in the largest quantity when the stream 

 rises in a cultivated country. 



Even in cases when the water used for flooding 

 is pure, and free from animal or vegetable sub- 



stances, it acts by causing the more equable dif- 

 fusion of nutritive matter existing in the land ; and 

 in very cold seasons it preserves the tender roots 

 and leaves of the grass from being affected by 

 frost. 



Water is of greater specific gravity at 42" Fah- 

 renheit, than at 32°; the freezing point ; and hence 

 in a meadow irrigated in winter, the water imme- 

 diately in contact with the grass is rarely below 

 40®, a deirree of temperature not at all prejudicial 

 to the living organs of plants. 



In 1804, in the month of March, I examined 

 the temperature in a water meadow near Hunger- 

 ford, in Berkshire, by a very delicate thermome- 

 ter. The temperature of the air at seven in the 

 morning was 29*^. The water was frozen above 

 the grass. The temperature of the soil below the 

 water in which the roots of the grass were fixed 

 was 430. 



In general those waters which breed the best 

 fish are the best fitted for watering meadows ; but 

 most of the benefits of irrigation may be derived 

 from any kind of water. It is, however, a gene- 

 ral principle, that waters containing ferrugi- 

 nous impregnations, though possessed of fertilizing 

 effects, when applied to a calcareous soil, are in- 

 jurious on soils that do not effervesce with acids ; 

 and that calcareous waters, which are known by 

 the earthy deposite they aflbrd when boiled, are 

 of most use on siliceous soils, or other soils contain- 

 ing no remarkable quantity of carbonate of lime. 

 The most important processes for improving 

 land are those which have been already discuss- 

 ed, and that are founded upon the circumstance of 

 removing certain constituents from the soil, or 

 adding others, or changing their nature ; but there 

 is an operation of very ancient practice still much 



* And, I may add, to counteract the effect of rain- 

 water, to dissolve and remove carbonate of lime from 

 the soil. In Malta, where irrigation is much employ- 

 ed, the water containing carbonate of lime, I tiave 

 found no deficiency of this compound in the soil of 

 the irrigated lands ; but in this country, even in chalk 

 districts, the superficial soil is often entirely destitute 

 of carbonate of lime ; it has been removed in process 

 of time, supposing that it previously existed in the 

 soil, by the solvent power of raiu-water. — J. D. 



