PRACTICAL IRRIGATION.

Dominion, Volume 5, Issue 1342, 20 January 1912, Page 14

PRACTICAL IRRIGATION.

« THE SOU* CBy John MUenguo.) l • IL (Copyright.) The soil ig a. product made or manufactured by the natural agents—the atmosphere, water, tlio rojts of plants, cold, and the grinding action of ico anil the tides. The action of the atmosphere, and chiefly ils carbonic acid, in wearing down rooks, ia well known. Ex-pose tho surface of a freshly quarried rock to the air, and Boon its fresh and generally bright appearance will disappear. The carbonic acid has overcome the adhesive, binding power or force that kept the particles so firmly together. If the rock be so porous as to admit the smallest portion of water, a further poworful agent in the crumbling process gets to work. The carbonic -acid in the rain water acts, as it acted in tho cisj of the atmosphere. But, further, should the temperature fall to, or below, the freezing point, the water in the pores and interstices of the rock freezes, and expaaling, forces the pn.rticlcs, or even portions of the rock, asunder. The grinding action of moving ice, of rivers, and of the tides aro further examples of the grinding down and orumbling of rocks. In process of time, the boundary of organised matter crossed, the roots of the lowest forms of plants tako roat in the newly-formed soil, grow, die, and add organic matter to the soil. If the rock from which the soil has been formed be limestone, the soil will be calcareous; if feldspathic, the soil will be clay, if silicious the soil will bo sandy or gravelly. As tho growth of the vegetable world increases, masses of vegetable matter, die,' decay, and form 'peaty soil, and loam. The decayed vegetable matter is' known aa the organic portion' of the soil; and crumbled rock as the inorganic In the course of countless centuries of years, the soil as we know it has been formed, and a fertile soil will generally contain about nine-tenths inorganic • and about one-tenth organic matter. The similarity between the constituents of tho soil and of plants may be set forth thus: THE SOIL AND CROPS., Organic Portion Of Soil. Of Crops. Carbon Woody Fibre Hydrogen Starch . Oxygen Sugar Nitrogen Gum Sulphur Albuminoids Phosphorus Gluten Oil Tats Inorganic Portion Of Soil. Of Cropt. Sand : ■ . s Silica Clay Clay . Lime Lime 1 Potash Potash Soda • Soda Magnesia Magnesia Oxide of Iron Oxide of Iron Oxide of Manganese — Sulphuric Acid Sulphuric Acid Phosphoric Acid Phosphoric Acid Chlorine Chlorine lodine - lodine Bromine Bromine Fluorine Fluorine While'it is true that chemists can often detect traces of substances in plants that they cannot detect in the soils in which tho plants grow, it is nevertheless true that the inorganic substances of . the soil and of the crops are practically the same, and also that tho organic portions of the crops may be reduced to the organic portions of the soils. The crops simply feed on the prepared portions of the soil that they; require., But the proportions of organic matter', arid of inorganic matter, are very, different in. different classes of soil. In burning an I average soil, out of every 100 pounds it would be found that from 90 to 98 pounds are inorganic! and only from 4 to 10 pounds organic. But in a peat soil the proportions would be about GO to 80 pounds organic, and from 20 to 40 pounds inorganic. Nature in her laboratory in the soil is ever busy, during the months while plant life is active and growing, in preparing food for tho nourishment of tho vegetable kingdom. The increasing warmth' of spring is the magician's wand that sets the soil laboratory at work. The rain water filters through the soil, and, aided by the carbonic acid of tho rain water, dissolves tho plant foods. When the hairs on : the' rootlets of the young plants have attached themselves to the particles of tho soil, these hairs exude a further chemical substance or acid, which enables further plant food to be dissolved from the soil, and to be reduced to a condition suitable for the roots to absorb in much the same way as oil will pass through a thin membrane. It is plain that if the soil bo in the condition of a compact, hard mass, the rain water will not be able to percolate through the soil; and the air will not bo able to circulate between the particles that form the soil. The Need For Drainage. The soil must be thoroughly tilled that the water may, in its passage through, perform its part in' dissolving tho plantfood; and that the air, with its accompanying carbonic acid, may also have the opportunity to do its requisite work. If the water remain permanently in the soil, stagnation will result, injurious gases will be formed, and plants will sicken and die. The need of drainage to carry away the water which has done its work is apparent. Tho height at which the water remains or stands, at some distance from the surface, is called tho "watertable"; and it is higher or lower as the rainfall varies. As a rule, plants flourish best when the "water-table" is several feel from the surface. If too close to the surface, the rain water and the air cannot percolate and circulate through the soil; and stagnant water with injurious gases results, Tho temperature is also lowered. It is important that the soil be capable of holding and retaining for a time a large supply of rain water. A clay soil retains the rain water too long;_ a sandy soil not long enough. Then again, a good deal depends upon the subsoil. The drainage must be capable of allowing the used-up rain -water to freely leave the soil lying between t{io surface and the "water-table." In that layer of soil and subsoil, rain water has two movements:—(l) Percolation downwards towards the sea; the river, or lake. (2) A movement in all directions in those parts'of the soil which are above the water-table. Percolation is' a slow movement in any ease; and the water finds its way through the soil much slower, in wooded country and through clay soil, than from a bare country, and sandy soil. A dry soil is like a dry sponge; it absorbs the water from the water-table much as a wick draws up tlie oil in a lamp. (1) The particles and pores of tho soil absorb and hold rain water that comes to them from above. (2) The particles of soil and tho pores above the water-table suck up moisture from it. Hence, while the used-up rain water is drained away, each particle of the soil is kept constantly moist; and as this moisture, in conjunction with tho carbonic acid in the rain water, and tho chemical acids exlided by the hairs on the -rooH«f« of the plants, is used up by the plants in the shape, in part, of the manufactured plant food, fresh supplies , take its place. The further movement of. the water, in the shape of moisture, may bo, by evaporation from the soil, or by exhalation from tho leaves of plants and tho foliage of other vegetablo plant life. Frequent Tillage Valuable. The movements of the water through the soil are greatly facilitated by keeping the soil in a fine porous condition by frequent tillage. The air will also circulate more freeljr through such a soil. To ensure tho fertility of the soil, it thus seems necessary to plough deep. By so doing, the air can circulate freely through it and is free to play its part in converting parts of the soil into plant food. Besides, with deep tillage, the roots of the young plants can descend deeper into the soil; can obtain more plant food, and can withstand the effects of drought much better. Even in cases where the subsoil contains substances injurious to the young plant, the subsoil ploash ought to be used to stir up the subsoil without bringing it to tho surface. In this way free play is given to tho action of both air and moisture in tho layers of tho soil that furnish food for tho young and growing plant. But the best tillage is largely useless lEitboiit efficient drainage. And this applies with added force in the case of heavy or clay land; and where any soil is irrigated. The depth of drains depends on tho surrounding circumstances—the outlet • for

tho water aad tho nature of the soil. Peaty land requires deeper drains than light laud. As a rule, deep drainage « preferable; because then the water and the air in their passago through tho soil act on a larger body of soil, and convert moro of its substances into plant food. In a favourable soil tho roots of plants, such as clover and turnips, go down deep into the soil; and with shallow drainage a sufficient supply of plant food would not be available.. Deop-rootcd crops often look well at first, and afterwards sicken and fail, and. this very frequently happens in the presence of unskilful irrigation. The cause is not hard to find. Water lias collected and become stagnant; unhealthy compounds and hence unhealthy ill ant foods have been formed, and wiien the roots of the growing plants have descended into the soil 'to tho depth at which this unhealthy plant food exists, tho sickening of the plant commences. A fertile soil will have these properties:— (1) The water table will be at a depth from tho surfaco of the soil to allow plenty of soil and subsoil for tillage, and for the roots of all ordinary farm crops above the water table. (2) Density. (3) Capacity for absorbing and retaining moisture without. impeding capillary circulation. (4) Porosity, or capacity for allowing water to pass through it. '(5) Temperature suited to the needs oi growing plants. If the density of the soil, such as srtifi clay, bo too great, : it may possess othei desirable qualities, and yet be useless for agricultural purposes. If its capacity foi absorbing and retaining moisture bo toe great or too little, the soil may possess other desirable qualities, and yet bo unfitted to grow farm crops. If its temperature lie too high or too low, it uiaj possess other ' ,o sirab!o qualities, and yet be unfitted to grow farm crops. Waterlogged clay or peat is an example of the former; decomposing vegetable matter oi the latter. (li Pure sand will hardlj retain 5 per cent, of its weight of water. (2) Stiff clay will retain 50 per cent, oi its weight of water, and yet appear dry, (3) Clay soil will retain three times, oi more, as much water as soil of a sand,v nature. (4) In dry, hot weather, soil of ii sandy nature will give off the saint weight of water, in the form of vapour, in one-third of the time necessary tij evaporate the same volumo from stiff clay, p°at, or rich mould. (5) In drying, sandy soils do not contract. (G) In drying, peat land and strong.clay land, shrink one-fifth of their bulk. A\ ith a knowledge of these properties of the various classes of soil, many useful deductions may be made. It is casv to see why it is desirable to mix sandv soil 'nth clay; that, after rain or irripatlng, soils of a sandy nature should" Ik left untouched as far as possible; thai peat Kill and rich mould, if the crop allow of tillage, should lie cultivated after ram; and that strong clay land should be , tilled for tho double purpose of gettin" rid of the superfluous water, and loosen" ing the soil around the roots of the Pj? j • .4" conditions may be complied with, and yet without an adequate supply of water available at the pronei time sterility may result. With an intermittent supply at improper times, the best that can result are stunted crops, barren fields, and serious pecuniary lcs< to a discontented and disheartened peo': pie; aa in India and parts of America prior to the advent of irrigation in those countries. All this may be avoided by a . proper system of irrigation. Preparation of the Land. It is important that the land bo nrownllfr pr E? !lr< s j or applying irrigatingii- f he sm "'ace of the soil be dotted by hillocks, hollows, or holes, or other inequalities in height of tho surtace, the irrigating water will probably do more harm than good. The preparation of the land, which includes the levelling, is as necessary as securing the water for irrigating. In preparing the fiold for irrigation, it is/iiecessary to first determine m wnat direction the irrigating • channels will run. The land is then ploughed m tho same direction. When it- has been ploughed and sufficiently harrowed, should any inequalities exist, a levelling machine should be used. One term of this machine consists of two longitudinal beams, each beam twelve feet in length, and six inches by three. ■Lhreo pieces, each nine feet in length, and six inches by tlireo, are bolted on iu front, and underneath to the longitudinal beams, in iiooring-board fashion. Four additional and similar pieces aro bolted to the longitudinal beams behind and undenieaHi, but ia weather-board fashion, with the edges set • forward. Halfway between these two sets of planks a wooden scraper is placed, faced underneath and in front with a stoel plate three inches by a quarter inch. In front of this scraper there are three eyebolts which swing on a round bar oi' iron. There is also a- five-feet lever bolted on to tho back of this scraper, with a crank underneath it. The horses are yoked to this levelling-machine, and when it comes to aciay li/np the driver stands on tho lever, and forces the scraper into tho earth, which is pushed forward until it comes to a hollow. The driver then steps on the crank, which turns upwards, and lifts the lover, when the scraper swings backwards, and deposits tlie earth. The weather-board edges of the planks behind them level the heap, and break any lumps. This levelling machine can be worked by four horses and. a man, and will level from fivo to six acres a day. Iu every country in which irrigation has been practised it has been found, sooner or later, that tho soil bccomes saturated; and hence tho importance of 'an efficient system of drainage deep enough, to carry off all superfluous water, and prevent tho permanent level of tho underground water rising higher than the lowest level to which tho root 3 of growing plants descend. Should this happen, the crops sicken, and will ultimately die. The permanent standing water has already exhausted its capacity for dissolving plant food, and in addition to being useless for this purpose, it prevents the passage of the air and the rain-water through tho soil. When the water ascends to the surface, or when, from defective drainage, the irrigating water is allowed to remain in pools on the surface, the effects on plant life are disastrous. Lord St. Osnald has given the sum of .£3OOO towards the restoration of Frodingham Church (Lincolnshire), the tower ,of which was built in the fifteenth century. The Eev. W. R. Daine. vicar of St. St.vthians, near Redruth, Cornwall, was killed through being thrown from an omnibus, the horses of which had rnn away. An English paper relates the following story:—'A few days since a battleship was cautiously feeling her way through a fog in Torbay. Suddenly the navigator on the bridge heard church bells startlingly near. As he believed tho land to be four or fivo milos away ho panicked on the engine telegraph, and ordered the leadsman to sound. Tlie result showed plenty of water._ Again the perplexing church bells chimed, clear and near. Tlvo face of tho helmsman relaxed. Asked sharply what he meant by grinning in a moment of danger, the man explained that it was one of the crew trying his new phonograph records in the niess flat t'or'rardl"