:'^30 SCIENCE OF AGRICULTURE. Part II. 



additions to the soil has long ])oen practised, and is an evident imitation of the overflowing 

 of alluvial lands, whether in meadow or aration. In the former case it is called irrigation 

 or flooding, and in the latter warping. Warping is used chiefly as a mode of enriching 

 the soil by an increase of the alluvial depositions, or warp of rivers, during winter, where 

 the surface is not under crop, and is common on the banks of the Ouse. 



2208. The Italian process called colmata {fullness) is nothing more than a variety of the British process 

 called warping. In the Val di Chiana in Tuscany, fields which are too low are raised and fertilised by the 

 process called colmata, which is done in the following manner : The field is surrounded by an embank- 

 ment to confine the water ; the dike of the rivulet is broken down so as to admit the muddy water of the 

 high floods; the Chiana itself is too powerful a body of water to be lised for this purpose, it is only the 

 streams that flow into the Chiana that are used. This water is allowed to settle and deposit its mud on 

 the field. The water is then let off into the river at the lower end of the field by a discharging course 

 called scolo, and, in French, canal d' earn lenient. The water-course which conducts the water from a 

 river, either to a fall for irrigation, or to a mill, is called gora. In this manner a field will be raised five 

 and a half, and sometimes seven and a half feet, in ten years. If the dike is broken down to the bottom, 

 the field will be raised the same height in seven years ; but then, in this case, gravel is also carried in 

 along with the mud. In a field of twenty-five acres, which had been six years under the process of colmata, 

 in which the dike was broken down to within three feet of the bottom, the process was seen to be so far 

 advanced that only another year was requisite for its completion. The floods in this instance had been 

 much charged with soil. The water which comes oflT cultivated land completes the process sooner than 

 that which comes ofT hill and woodlands. Almost the whole of the Val di Chiana has been raised by the 

 process of colmata. 



2209. A proprietor whose field is not adjacent to a stream may conduct the stream through the inter- 

 vening lands of another proprietor on paying the damage he occasions. The process of colmata is 

 expensive, because the ground is unproductive during the seven or eight years that the process lasts ; but 

 this is soon repaid with great profit by the fertility of the newly deposited soil. 



2210. By the gravel which the rivers carry and deposit their bed is much raised above the level of the 

 adjoining fields ; so that, in order to carry off the rain water from the fields, drains are formed which 

 pass in arched conduits under the embanked rivers, and go into larger drains which pass to the lowest 

 part of the plain jiear Arezzo, and there enter the Chiana. 



2211. The soil in the Val di Chiana is generally the same to the depth of six feet from the surface, and 

 under that is gravel or sand. After the completion of the process of colmata, the expense of which is 

 always repaid with profit, the ground is cultivated for five years on the proprietor's own account ; and the 

 produce during these five years repays the expense of the process of colmata with profit. The first two 

 years it is sown with Indian corn (granturco), and sometimes hemp, the soil being then too strong for 

 wheat. The next three it is sown with wheat, without any manure. Tlie produce of wheat in this highly 

 fertile state of the soil is twenty from one, whilst in the usual state of the ground the return of wheat is 

 from twelve to fourteen from one. After this the field is let out in the ordinary way to the farmers, the 

 contadini. {Farm. Mag., vol. xxi.) 



2212. The rationale of irrigation is thus given by Sir H. Davy: " In general, in 

 nature, the operation of water is to bring earthy substances into an extreme state of 

 division : but in the artificial watering 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 winter, or in the begin- 

 ning of spring, the moisture which has penetrated deep into the soil, and even the subsoil, 

 becomes a source of nourishment to the roots of the plants in the summer, and prevents 

 those bad effects which often happen in lands in their natural state, from a long con- 

 tinuance 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 ; or which exists in the largest quantity when the stream rises in a 

 cultivated country. Even in cases where the water used for flooding is pure, and free 

 from animal or vegetable substances, it acts by causing a more equable diffusion 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 Fahrenheit, than at 32", the freezing point ; and hence, in a meadow 

 irrigated in winter, the water immediately in contact with the grass is rarely below 40, 

 a degree of temperature not at all prejudicial to the living organs of plants. In 1804, in 

 the month of March, the temperature in a water meadow near Hungerford was 

 examined by a very delicate thermometer. 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 43^^." Water may also 

 operate usefully in warm seasons by moderating temperature, and thus retarding the 

 over-rapid progress of vegetation. The consequence of this retardation will be greater 

 magnitude and improved texture of the grosser parts of plants, a more perfect and 

 ample developement of their finer parts, and, above all, an increase in the size of their 

 fruits and seeds. We apprehend this to be one of the principal uses of flooding rice- 

 grounds in the East; for it is ascertained that the rice-plant will perfect its seeds in 

 Europe, and even in this country, without any water beyond what is furnished by the 

 weather, and the natural moisture of a well constituted soil. It may also be noticed that 

 one variety of rice grows on the declivities of hills without artificial irrigation ; as in St. 

 Domingo and in certain parts of India. " 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 general principle, that waters con- 

 taining ferruginous impregnation, though possessed of fertilising effects ^yhen applied to 



