IRRIGATION.

Otago Witness, Issue 3111, 29 October 1913, Page 21

IRRIGATION.

By John M’Keague.

IN PRACTICE

(Copyright.)

In virgin country farmers are liable to make mistakes that seldom fail to bring retribution. A settler cuts down the bush or forest, burns the timber; and, finding it an easy matter to get good crops from the virgin soil, thinks that like good crops will continue to\grow under like conditions year by year In duo time, and at his cost he finds his mistake. That mistake is that he grows his crops at the expense of decreas-ing-.capital The soil is much in the position of a housewife who has laid in a stock of different provisions or foodstutts. Everything goes well as long as the provisions last. But wheih. one or more has been consumed trouble commences. the efficient housekeeper will see that supplies ere kept up, in order to avoid famine. And so it is of the soil. In the virgin soil there are usually abundant supplies of the various plant foods. But if crops be constantly grown, and corresponding supplies ot manures be not returned to the soil, it is only a matter of time until soil exhaustion lesults. No farmer can continue to grow crops, graze his stock, or otherwise exhaust the soif unices he return to the soil, m the shape of manures, the constituents of which it was deprived bv the growing crops or trie frazing live stock. Hence the importance of farmers undertaking the general make-up of the soil, and on what its fortuity depends. The coil is a product made or manufactured by natural agencies-the atmosphere. the roots of plants, e°ld, and the grinding action of ice and of . - ... ' The a ebon of the atmosphere, and the carbonic acid m the atmospho.e, m wearing down rooks is wed know . the surface of a freshly-quarried rook to the air, dnd soc.n it? fresh and generally brighappearance disappears The atonic acid has overcome the adhesive and binding powers that kept the particles bound so firmly together. If the rock be so porous as to admit the smallest particle of water, another powerful force comes into act on, ine water freezes, and, in doing so, expands, and forces the particles of the rock asunaer. In these, and in other ways, the part of the soil derived from rocks was formed, and it known as the inorganic part of the soil, in duo time Plants and vegetable life generally find a home in the soil, and having grown and died they add a fresh clement to the soil. This is known as the organic or vegetable part of the soil, and its fertility largely depends on the composition and qualities of the organic and the inorganic parts. me crops grown by farmers extract, in the shape of plant food, much of tho constituents of the* inorganic and organic parts of the- soil. The different constituents have different names; and that tho drain, or the demand of the crops for plant fowl, from “ le f 0 is serious is shown from the following table:

Sou. Constituents in average Grots.

ManWheat. Barley. Swedes, golds. Hay.

Farmers will thus see the constant and heavy drain from the soil ot the plant foods or constituents known as n.trogcn, [jot-ash, phosphoric acid, lime. an<l silica, wnile in the case of mangolds not only is the demand on these substances exceptionally heavy, but also on the subotanccs shown in the table. While a virgin toil may stand that dram lor a time, it can be for a time only; wd. unless these substances extracted from the soil by the growing crops be returned to it in the shape of manure, the exhaustion of the soil is a certain consequence. The up-to-date farmer must not only understand tho composition of tho soil, but also the best methods by which its fertility may be kept up. While it is true that chemists can often detect traces of substances in plants which they cannot detect in the soils wherein the plants grow, it is true, nevertheless, that the inorganic substances of the soil and of the crop are practically the same, and that the organic parts of the soil and of tho crop are also the same. The crops simply feed % on those substances in tho soil which have

been prepared for food for the plants. But v tho proportion of organic a/:d of inorganic substances is very different in different soils ard classes of soil. If a' soil be burnt on a red hot plate, speaking generally, the organic part will fly off, and the inorganic part will be left on’ the plate in the shape of ash. In the burning of an average soil it would bo found that out of every hundred parts from 90 to 93 parts are inorganic, and from 2 to 10 parts organic. But in a peat soil the proportions would be about 60 to 80 parts inorganic, and from 20 to 40 parts organic. Hence farmers will readily see that the first step towards growing crops, or feeding live stock successfully and profitably, is to have the soil constantly in a condition to furnish, under efficient tillage, tho materials for the plant food necessary for the growing crops. Nature, in her laboratory in tho soil, is ever busy during the months while plant life is active, in preparing food for the nourishment of the growing plants and crops. Tho increasing ■warmth of spring is the magician’s wand that sets the soil laboratory at work. Tho winter rains have penetrated through the soil, and, aided by the carbonic acid in the rain water, dissolved the plant-foods. When the hairs on the rootlets of tho young plants have attached themselves to the particles of soil, they exude a further chemical substance, which further aids in the preparation of the plant-food, which finally passes through tho walls or outside surfaces of the colls of the roots and rootlets in much the same way as oil will pass through a thin membrane; and tho plantfood rises from the roots through the trunks, branches, and leaves of trees or plants in much the same way as oil rises through the wick of a lamp. But if the soil be not properly tilled, the rain wj*ter and the air will not find their way through the soil, plant-food will not be prepared

in the soil, and the crops will be a failure. The soil must bo thoroughly tilled that the rain water and the air may freely pass through it. and if the soil be thus left to the action of frost, further .beneficial results, as regards the supply of plant-food, will follow. But if the water be allowed to remain permanently in the soil it will become stagnant, the soil swampy and cold, and the crops will not grow. On the other hand, if there be not sufficient moisture in the soil, drought will result; and farmers will suffer serious losses. Having prepared the soil, and efficiently regulated the moisture, then take a seed of any ordinary farm crop, and first place it in dry mould. The seed will not germinate or grow. Moisten tho dry mould, but keep the seed and the mould at or below the freezing point, and still the seed will not germinate. Now place the seed in moisf soil and in a temperature at or below the freezing point, but exclude the air, and still the seed will not germinate. But if the air be allowed to come in contact with the seed, and to circulate through the moist, warm air, it will germinate, and the plant will grow provided there is a supply of plant food in the soil. It thus appears that the conditions necessary for the germination of the seed are—(a) Moisture; (b) warmth; (c) air. And, when the young plant begins to grow, further necessaries are—(d) plant food derived from the soil; (c) sunlight. It is important that soil be capable of holding a,nd retaining for a time a large supply of water. Most plants and crops that farmers grow use up in water 200 times their dry weight. A single plant of barley, in full growth and vigour, will require tho passage through it. while in the soil, of more than a gallon of water. An acre of cabbages in full growth will use tons of water in the course of a day. Even in dry weather, if a cold bellglass bo placed over grass, water enough to trickle down its sides will be deposited very soon. Farmers will thus see that a supply of moisture in the soil is of the first importance. The farmer may till his soil by the best methods, but in the absence of moisture crops will not grow. The height at which the water stands at some distance from the surface is called the water table, and it is higher or lower as the rainfall varies. Plants as a rule flourish best when the water table is several feet from the surface of the land. In the layers of soil and subsoil, between the water table and tho surface of the land, rain or other water has two movements: 1. Downwards towards the sea, the river, or the lake. 2. A movement in all directions, in the soil or subsoil, above the water table. These movements of the water are slow, and much slower in wooded country than in country which is naturally bare of forests, or in countries which have been stripped of their natural forests. In the North Island of New Zealand large tracts of country have had their forests or bush cut down to provide agricultural or grazing land. Tho three natural condensers of rain are; (1) Trees and forests, (2) hills and mountains, (3) cold derived from any source Many instances might bo given, as those of Honolulu and Trinidad. Forests originally existed ih both; and in each, when the forests were destroyed, the rainfall largely decreased, and the rains fell at irregular periods. No sooner had trees been extensively grown again than the rainfall increased, and the rains fell at regular times. The Waikato also has suffered from drought, especially as regards dairying. Dairy cows do best in cool, moist weather, and with plenty of tender, succulent grass. When drought visited the Waikato (and elsewhere) dairy farmers suffered severely. Settlors, who had leased lands, bought cows, and made their arrangements, as based on the experience of former seasons, wore largely ruined. At one creamery the number of dairy farmers and tho number of cows were greater during the year of drought than during tho preceding year. Yet in tho drought year on'y 17,747 . gallons of milk were received, as compared with 23,084 gallons the preecd’ng year. And this is only one example from many. If, then, dairy farmers and farmers in general can so control matters that they may avoid such losses, it will pay them well to do so. The movements of the wa f er through tho soil are greatly facilitated by keeping the soil in a fine, porous qondition by frequent tillage. Tho air will also circulate more freelv through such a soil. To assure tho fertility of Ihe soil it is necessary to plough deep and thoroughly to till the soil. Soil so treated will retain more 'moisture, -nd tho free passage of tho a ; r through it will convert more of its constituents into plant food. Where the land is of such nature that water is apt to lodge in tho soil and become stagnant, tho drainage system must be thorough, and tire drains must be deep enough to allow the roots of such crops as clover and turnips, which go down deep into the soil, to obtain sufficient moisture without coming in contact with stagnant water. Deep-rooted plants often start well, and look healthy at first, but, then sicken, and the crop fails. The cause is not hard to find. The roots of the voung plants, not having gone deep enough to come in contact with stagnant water, had healthy plant food, and while this was so, they grew and flourished. But as soon as the roots hail gone deep enough to come in contact with tho stagnant water, the plant food was no longer healthy, and tho planks and crops sickened and failed. A good, fertile soil will have these properties: (1) The water table will be at a depth from tho surface of tho land to allow v plenty of the 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 the power or capacity for allowing water to pass through it. (5) Temperature suited to tho needs of the growing plant. If the density of the soil, such as stiff clay, bo too great, it may possess other desirable qualities, and yet be useless for agricultural purposes. If its capacity for absorbing and retaining moisture be too great or too little, the soil may possess other desirable qualities, and yet bo useless. If its temperature be too high or too low, it may possess other desirable qualities, hut yet be useless to grow farm crops. Decomposing vegetable matter is an example of the former; water-logged clay or peat land an example of the latter. (1) Pure eand will hardly retain 5 per cent, of its weight of water. (2) Stiff clay will retain 50 per cent, of its weight of water, and yet appear dry. (3) Clay soil will retain three times (or more) as much water as soil of a Bandy nature.

(4) In hot, dry weather, so., of a sandy nature wil|_ give off the same weight of water, in the form of vapour, in one-third of the time necessary to evaporate the same volume from stiff clay, peat, or rich mould. (5) In drying sandy soils do not contract. (6) In drying peat land and strong clay land shrink about one-fifth of their bulk. With a knowledge of the various classes of soil, and their various properties, the farmer may make many useful deductions. He will see why it is desirable to mix sandy soil with day, clay or sand with peat, and such like. lie wul also see why it is desirable to leave soils of a sandy nature untouched after rain; .why peaty soil and rich loam should be cultivated alter rain; and why strong clay land should be cultivated after rain, for the double purpose of getting rid of the superfluous water and loosening the soil around the roots of the plants, that the air may circulate freely through the soil. • For the purposes of irrigation, should the surface of the land be dotted with afllocks and hollows or holes, the irrigating V'ater will probably do more harm than good. The preparation, which includes the levelling of the land, is as necessary as securing the water for irrigation. In the preparation of fields for irrigation it is necessary first to determine in what direction the irrigation channels will run. The land is then ploughed in the same direction. When the land has been ploughed and sufficiently harrowed, should any inequalities exist, a levelling machine is used. ihat in use in Victoria consists of two longitudinal beams, each 12ft in length, and bin by 3in. Three pieces, each Hit long and bin by 3;n, lira boited on in front and underneath to the longitudinal beams in flooring-board fashion. Four additional and similar pieces are bolted to the longitudinal beams behind and underbeath, but in weatherboard fashion, with the edges set forward. ‘Half-way between thee© two sets of planks a wooden scraper is placed, faced underneath and in front with a steel plate 3.n by iin. In front of this scraper there are three eyebolts which swing on a round bar of iron. There is alco a sft lever bolted on to the back of this scraper, with a crank underneath it. The horsce are yoked to this levelling machine, and when it comes to a clay lump the driver stands on the lever and forces the scraper into the earth, which is pushed forward until it comes to a hollow. The driver then steps on the crank, which turns upwards, and lifts the lever, when the scraper swings backward and deposits the earth. The weatherboard edges of the planks behind them level the heap and break any lumps. This machine is worked by four horses and one man, and will level from five to six acres a day. The supply channels, or field watercourses are made with a V-shaped scraper or delver plough A single-furrow plough first turns a single furrow; and, the delver plough following, the furrow is, removed and placed in position to form one bank of the channel. A second turn of the plough forms other bank, and the watej, channel is practically completed. Should it be considered desirable to stop the flow of water at any point in these channels, stop bars arc constructed across the channel. Three small posts. 2ft apart, are driven into the ground on each side of the channel. The post on each side farthest up the current is placed about a foot farther back from the channel than the others so as to form a wing. Slabs are nailed to these, and a wooden floor is laid down. A couple of skids are nailed on each side wall to allow a shutter to slide up and down. When the shutter is put down and a few shovelsful of earth thrown in hardly any water escapes. Should it bo necessary temporarily to stop the current at any other point, sacks filled with straw are placed across the stream. Drains must be constructed to carry away the superfluous water, as well as to drain the subsoil, which, if left constantly saturated, will effectively ruin plant life. The distance the irrigating channels and the drains arc apart depends on the slope of the land, and on the quality of the soil and the subsoil.

| Tons. Tons. Tons Tons. Ton? Crop. 1 2.2 2.0 16.1 30.1 1.5 lbs. lbs. lbs. lbs. Nitrogen Soda .. 50.0 .. 2.6 .. 28.8 49.0 5.0 3o.j 98.0 32.0 79.7 149.0 118.7 300.7 49.0 9.2 50.0 Magnesia Lime .. 7.1 .. 9.2 6.9 9.2 9.2 42.4 42.5 42.9 14.4 32.1 Phosphoric . 21.1 20.7 21.7 52.9 12.3 Sulphur .. 7.8 .. 2.5 6.1 4.1 17.8 15.1 14.0 83.1 5.7 14.6 Silica .. 98.9 68.6 6.7 17.9 56.9