FARM DRAINAGE

New Zealand Journal of Agriculture, Volume 74, Issue 1, 15 January 1947, Page 67

FARM DRAINAGE

By

N. LAMONT,

Assistant Irrigation Officer, Christchurch.

TN districts of moderate to high rainfall no other farm operation ■*- is of such fundamental importance as soil drainage, which, if inadequate, will limit the success of almost all farm work. Pedigree seeds and pedigree stock will not thrive nor will the best of fertilisers be effective if, for substantial periods of the year, the soil is cold and soggy with surplus water.

IT is significant that as soon as settled farming evolved from primitive nomadic methods attention was at once directed to drainage. In the ancient Greek and Roman Empires use was made of stone, fascine, and tile drains. In England and Europe development in drainage practices was slow until about the seventeenth century, but

since then the subject has occupied a prominent place in agricultural literature - The earliest types of . drains used were fascines, or a variety of tiles, and, although mole drainage was in use about 100 years ago. it did not become popular until very recently, when the introduction of traction engines and tractors provided farmers with a source of power to do the work efficiently. In New Zealand in the early days an abundance of almost costless timber made box drains popular, but their use steadily declined as timber supplies became more scarce and tile manufacturing developed.

Basic Principles The simple object of drainage is to remove excess water from the topsoil within a few hours of rain. Soil in

structure is somewhat similar to a sponge with large and small pore spaces. The smaller pore spaces retain moisture by the force of capillarity—in the same way as blotting paper absorbs waterbut the larger, spaces in the soil allow water .to pass through under the influence of gravity. This proportion of the total water in a soilthe “gravitational” water of no use to a plant, its presence in fact being detrimental. Consequently, this is the water that must be removed by drainage. No amount of drainage or over-drainage will remove the “capillary” water from which the plant roots draw their supplies; this is lost only through the plant’s circulation system of the soil and through absorption by the plant roots, whence it is carried through the plant’s circulation system and passed out through the leaves by the normal process of tranpiration.

Light-textured or sandy soils have a high proportion of large pore spaces and, providing that an outlet exists, will permit gravitational water to escape quickly after rain. In closetextured clay soils the pore spaces are

usually small and the natural . soil channels are inadequate for the escape of surplus water before further rainfall again saturates the soil. Generally, a: soil can be considered to be adequately drained if the surface is firm and free from sogginess within 24 hours of a normally heavy winter rain;

Sometimes poor drainage o an area „ - , , i. x of ground may be the result of a clearly-defined source of water coming f rom a spring or from neighbouring higher ground, and may be corrected an intercepting drain to J . ~x, x,, x cut off the source of the excess water, More often saturation is caused oy the of the natural soil and subchannels to carry away the rain 7 fall falling O n the surface. The ground water level-the water-table-is built U P winter rains until it very frequj;ntly , coincides with the general s^ aCe leve ! ° f the . + 011 ' object of drainage is to maintain this watertable at a low level by providing

escape channels and so prevent it from building up close to the soil surface. Generally during dry summer weather the water-table falls below

the level of. artificial drains and these drains will not commence to function

in the autumn until sufficient rain has fallen to build up the water-table level to that of the drains. There is only one primary force that causes movement of free water in soils and that is the force of gravity which, of course, draws the water vertically downward. Horizontal movement takes place only when, under the influence of gravity, sideways movement becomes necessary to adjust water levels in the soil. The function of a drain is to fix the maximum height of the water-table level at the point of horizontal movement, so that if it is built up by heavy rain above drain level in the soil between the drains, the “gravity head” so established forces the water to move sideways to the drain, where it has a free outlet. The extent and speed of this horizontal movement depend on the difference created, in the water levelthat is, on the depth of the drain— on the resistance of the soil to the passage of the water, which is, of course, much greater in clay soils than in sandy ones.

Benefits of Drainage

Plant roots will not penetrate into soil that is saturated, and restricted root development means restricted leaf production. Also, a high spring watertable, by confining root development to the upper soil layers, will render the plant more susceptible to drought later in the season.

A healthy soil needs air as well as moisture. In particular, bacteria and other soil organisms responsible for the production of available nitrogen for plant food must have air if they are to function effectively and that is why one of the first symptoms of inadequate drainage is a yellow, stunted appearance of plants.

A drowned soil will rapidly deteriorate both in fertility and in its physical condition. In extreme cases substances poisonous to plants will be produced until eventually nothing will grow but weeds tolerant of these conditions. All farmers are familiar with the problems of cultivation of a soil that has been water-logged and with the practical impossibility of working down such soils to a sweet tilth. On the other hand, the texture of even a heavy soil improves after draining and a healthy “crumby” texture is developed, thereby permitting not only earlier cultivation in the spring, but a much more satisfactory seed-bed with less expenditure of labour and time, and giving higher yields of healthier crops.

All are familiar, too, with the cooling effect of evaporating moisture. A wet soil is cold, even though air temperatures may be warm, and consequently badly-drained soils are always backward in the spring until the surplus water has been removed

by evaporation. The sun raises the temperature of a well-drained soil quickly in the spring, and the passage of warm spring rains through freedraining ground warms the soil and draws behind it warm, fresh air to stimulate plant growth and soil health.

A healthy, well-drained soil means healthy stock, indirectly through increased pasture production, and directly in its effect on the health of animals, who do not have to live and sleep on waterlogged soil. Pedigree stock, pedigree seeds, rotational grazing, and topdressing all depend for complete exploitation on thorough soil drainage.

Depths and Distances

The ideal depth of drains is one which will permanently maintain the water-table low enough to permit plant roots to develop to their fullest extent, and will also operate at a depth beyond that dried out in the summer. In deep silty soils roots of ordinary crop and pasture plants may penetrate more than 4ft., but where a stiff clay subsoil is found about 12in. or so below the .surface it is unlikely that roots will penetrate far, even if it is well drained.

In deciding the depth at which to place drains it is necessary to consider the following points:—

(a) Outlets: It is possible to drain only to a depth permitted by the depth of the watercourses or streams into which the drainage outlets are to be led. Modern developments in drainage pumps and the usually very cheap operating costs of electric motors

occasionally permit farmers to create an artificially low outlet. Frequently a potentially-rich pocket of ground is virtually unproductive through the absence of a natural drainage outlet and a pumping scheme could be readily installed. Farmers who have areas of such land would be well advised to explore the possibilities of pump drainage; they would be surprised at the low cost of handling large volumes of water through the low lifts generally required.

(b) Protection: The drains must be deep . enough to be safe from damage by stock or implements.

(c) Power: In the case of mole drains the power available must be considered.

(d) Soil type: In deep silty soils drains may be 3 or 4ft. deep. Theoretically, even deeper drains could be installed and still be efficient at greater distances apart, but the extra cost of digging such drains would probably not compensate for the saving .in tiles. Where there is a welldefined, impermeable clay subsoil, 27in. to 3ft. is the usual depth for tiles, or 18in. to 2ft. for mole channels.

The distance between parallel drains depends on depth and soil type. In free-draining soils drains may be effective if the distance apart is 15 to 20 times the depththat is nearly a chain apart for drains three or more feet deep—but in heavy soils the distance apart may be only 4 to 6 times the depth, say Oft. to Bft. apart for drains 18in. deep. In practice drains are probably more often made too shallow than too deep. It is true that soil texture improves and becomes more porous as the result of draining, and drains that seem a little too deep and a little too far apart in the first season or two may prove completely satisfactory after a few years. '

Various Types

. A variety of materials has been used successfully for providing a channel for drainage water. In most cases, however, the labour cost in opening and closing drains is one of the biggest items of expense, and it is sound economy to employ permanent materials underground. On the other hand, the high transport cost of tiles or the need of only a temporary drain justifies the use of less satisfactory materials.

(a) Surface and Open Drains: Occasionally one sees an area ploughed in narrow lands, with or without an extra furrow turned in the hollows, the practice being described as surface. drainage. Although it has the advantage perhaps of preventing pools of water from accumulating, it can

hardly be called drainage, as it confers few, if any, of the benefits to soil and stock ’ that result from proper draining, since the soil is still saturated to the surface. Open drains serve a useful purpose as main drains alongside fences and as temporary measures during development. In peat swamps open drains must be used, as there is no solid bottom for tiles, and in any case progressive deepening will be necessary as the peat consolidates. As a general rule, however, their use is limited, and to permit the passage of cultivators and topdressing implements some form of closed channel is necessary.

(b) Fascine or Brush: This method has been employed for centuries, and when properly used is very successful. Fairly strong scrub is preferred, and it should be laid so that the butts of one bundle are covered by the brush of the next. Some difference of opinion exists as to whether the butts should point up or down the slope of the drain. It is argued by some that the ends of the stocks obstruct' the flow if pointing up the slope, but on the other hand the side branches ought to be equally obstructive if the ends point down /the slope. This does not seem to be a vital point, and good results may be obtained either way. It is generally advisable to tile or box 3 or 4yds. at the outlet of a fascine drain, as the material exposed to the air tends to rot quickly.

(c) Tiles: The most popular of covered drains is undoubtedly the tile drain and this will prove the most efficient on most soil types. The relatively high cost of tile drains must prevent their use on sticky clay soils where they would have to be very close together, and it is arguable whether

even a long-term view would justify their, use. In some clay soils after, say, - 15 to 20 years tiles appear to become sealed by gradual deposits of clay in the joints, so that in addition to being very much cheaper mole drains would seem to be the more efficient under such conditions.

(d) Mole Draining: Where there is a stiff clay subsoil, free from iron pan or other obstructions, and with a fairly even ground surface and a natural fall, mole draining can be employed satisfactorily. It is by far the cheapest method of draining and under suitable conditions is probably the most efficient.

The life, of mole drains depends on the suitability of the soil type and on the efficiency with which the work is carried out. Under good conditions individual mole drains can last more than 20 years, but a mole drain system would probably need to be renewed about every 10 years to ensure effectiveness. As its cost may be only about one-twentieth, of the cost of a tile system on heavy clay ground the use of the' mole drain method is fully justified. A full account of mole drainage methods, including the McLeod method, has already been given in “The N.Z. Journal of Agriculture,” of April, 1945, and all who contemplate draining a clay soil should give first consideration to the possibilities of mole drainage. The suitability of a subsoil for mole drainage can be judged reasonably well by moulding a piece in the hand; the plasticity will indicate whether a mole drain will be likely to stand. It will often be found that there is one layer of a clay soil, probably about 20in. deep, which may be more plastic than layers above or

below it; if possible, mole plough depth should be adjusted to ensure that channels are placed in this layer. Planning a Scheme The first step to be taken after deciding to drain an area is to locate suitable places for outlets. The following points should be borne in mind: — 1. Outlets are generally but not always at the lowest points in a. paddock. If these low points are likely to be flooded even temporarily, it is. better to leave a small area undrained than risk the success of the whole project. 2. Outlets should be placed so that they can serve any expansion of the original drainage scheme. 3. They should be placed where there is minimum risk of blockage by stock or other causes. 4. .It is possible to give more care to the protection of outlets and to their regular inspection during wet weather if the number is kept to a minimum. When the position of outlets is decided the whole scheme should be planned completely before the work is commenced. With carefully-selected outlets, it is possible to plan the mains, sub-mains (if necessary), and the subsidiary drains efficiently and economically. It is highly important also to prepare a reasonably-accurate plan of all drains, particularly tiles, laid on a property. It is quite impossible to rely on memory. The man who prepares an accurate plan will be amply repaid in time

and money saved when repairs or extensions become necessary. Should there be the slightest doubt as to the amount of fall available, some form of level should be employed. If a surveyor's instrument can be obtained so much the better, but if . not, a satisfactory substitute must be devised; never rely on guessing. Construction Methods A drainage system may consist of one or a combination of the different types of drains listed in the' foregoing. Probably the most popular are the “all-tile” systems and the mole drain systems with varying numbers of tiles for mains and outlets. Tile Drain Systems Except for clay soils suited to mole draining, there is no more efficient method of draining than by the modern, cylindrical tile or pipe. Providing the job is well done, the drains are more or less permanent, and they confer, immeasurable and cumulative benefits on soil, plants, and livestock. It is recorded that many years ago in America the neighbours of a certain farmer became very alarmed because they noticed that he dug clay from one part of his farm,. and after moulding and baking it carefully buried it again. Despite suggestions that he be put under restraint, this pioneer of tile draining required only a very few years to establish both his sanity and the benefits to be derived from efficient tile draining.

General Layout

It is impossible to give detailed suggestions that will fit every case and each paddock requires separate consideration. Having selected the position of the main outlets, it will usually be found that the mains and submains will be placed along natural depressions and hollows in the paddock or along the lowest side on flat, sloping country. As the mains and sub-mains are only carriers of water, the ground on each side of them being already ' drained by the subsidiary drains, it is sound economy to reduce their number to a minimum.

All drains and mains, particularly, should be as straight as possible. Sudden angles must be avoided. Rightangle junctions between subsidiary drains and the mains are also undesirable, and the former should be placed so that two do not enter the main exactly opposite each other.

Even in fairly heavy soils tile drains should have at least 2ft. clearance above themthat is, the drains, should be 27 to 30in. deep and in freer soils they may be as deep as 4ft. The width apart depends partly on soil type and and partly on depth. In heavy silt soils, with drains 3 to 4ft. deep, they may be a chain to a chain and a half apart, but on heavy soils drains every half-chain may be necessary.

As the permeability of soils improves after 3 or 5 years’ draining, the drains will gradually become effective over a wider area. If possible, each farmer should carry out some experiments to determine the depth and distance apart

that are efficient for drains under his own conditions. One or two drains can be laid in a paddock and their performance observed over two years or so before an expensive, large-scale project is installed. Capacity of Drains The capacity of a drain depends on the fall and diameter of the pipe. Very little fall will suffice in a well-laid pipe drain. Probably as little as 1 in 1.000 would be efficient. One in 300 is a fair gradient at which to aim. In most cases the contour of the . country will decide the matter. It is very important to avoid a loss of fall in the length of a drain, as this will inevitably lead to silting up, but a slight increase in fall is, of course, quite permissible. It is found in practice that tiles less than 2| to 3in. in . diameter are undesirable on account of the risk of displacement and blockage. Pipes of this size are large enough for all purposes except mains. As a rough guide, it is generally estimated that a pipe of 3in. diameter will carry all the water from 10 to 15 acres, a 4in. pipe will suffice for 15 to 20 acres, and so on. Although very approximate, this ‘ rule can be applied to drains of known length and distance, apart, and to mains receiving the discharge from subsidiary drains tapping a known area. Tiles more than 6in. in diameterwill rarely be required, and it should be remembered that by doubling the diameter of a pipe its capacity is increased four times.

Opening and Laying Draining is generally carried out during the winter, partly because at this season a farmer is most likely to have time to attend to such work, and partly because it is easier- to get a clean-bottomed trench under damp conditions. Furthermore, a small amount of water in a drain is a useful guide in obtaining an evenlygraded bottom. It is not advisable to open more drain than can be conveniently finished in a short time, or to dig the whole system partly and leave the cleaning of the bottom until the tiles can be laid without delay, otherwise weathering or scouring can cause a good deal of trouble. It will be found that an even depth can be maintained more easily by commencing to dig from the lowest end of the - drain and this will, of course, permit any water that may accumulate to drain away instead of banking up where the work is being done. A substantial amount of labour can be saved by turning the first spit with a single-furrow .plough. A tile drain trench. should not be wider than strictly necessary, and the sides should be trimmed smooth to reduce the risk of small lumps falling in while the tiles are being laid. For a thorough job a draining spade and scoop are essential. The last spit should be dug with the draining spade, giving a bottom that is only just wider than the tile itself When this is cleaned and shaped with the scoop the tile will bed down , neatly without risk of displacement.

Should a portion of the drain be accidentally dug too deeply, every effort should be made to grade out the depression without losing fall rather than to build up the bottom with loose soil, as it is essential that the tiles rest on a solid foundation. If the bed is loose, displacements must occur.

Even the best of tiles may not be precisely square on the ends, and they should, if necessary, be turned to make a close joint at the top to prevent soil from getting in. It is not desirable to force the tiles hard against each other, but even on moderate slopes laying should commence at the lower end to ensure that a tile does not move away from its neighbour.

Filling In

All drainers agree that the topsoil should be thrown on one side of the drain and the subsoil on the other, but there is a difference of opinion as to .whether the topsoil or the clay should be returned first. The object of returning the porous topsoil first is to. permit the water to enter the tiles more readily. However, water enters the tiles from below, and the placing of loose topsoil on the tiles merely increases the risk of silting. It is therefore recommended that the subsoil be returned to the drain first, and it will be found that the drain not only will function as well, but will probably remain efficient for a longer time. Even when mole drains are being drawn over the tiles it will be found that the disturbed clay will permit water to pass from the moles into the tiles, and when it has settled down channels will still remain.

The laying of tile drains is fairly expensive, but they have a very long life. Meticulous care and thoroughness should be applied, to ensure that efficiency of operation and long life are secured. , . •

Conclusion

In conclusion it may be stressed again that an adequate drainage system is one of the foundations of the whole farm business. Whatever method of draining is chosen, and there are many methods to fit many circumstances, the same principles apply and the same rules should be followed. First, thoroughly plan out the whole system before turning the first sod; secondly, obtain maximum efficiency throughout the life of the system by attention to detail and thoroughness; and finally, prepare an accurate and a permanent plan of the whole system.

Answer +0 Correspondent

“H.W.G.,” Dannevirke:— Could you let me know the opinion of your experts with reference to drenching, say, with nicotine and bluestone, particularly the following:— Does the drench kill (a) the worms, (b) the eggs; if not, do the evacuated worms or eggs contaminate the pastures? If so, for what period? Which chemical does the job? Is arsenic or other poisons a benefit? Is it necessary to drench more than once for lambs going into the works? If the worms are evacuated alive, would it not be a greater benefit to leave them in the animals, to be dealt with in the works, than to spoil the pastures? What are your recommended formulae for the nicotine bluestone drench and dose? ' ■ ' LIVESTOCK DIVISION:— Drenches such as bluestone-nicotine kill the worms and most of the immature eggs at that .time within the reproductive organs of the worm. Those eggs which are almost on the point of being excreted would probably resist the effect of the drench and might, to a small degree, infect pasture, but this infection would not be any heavier than that deposited by

an undrenched animal m a single day, when the number of eggs deposited

in the droppings might be 800,000 in a heavily-infested animal.

While strongly-resistant larvae may remain alive and infective on the pastures for months —up to 12 months—the large majority die within three weeks, and if a pasture can be spelled for that length of time, infectivity is much reduced.

Incidentally, when phenothiazine is given as a drench, or more particularly in repeated small amounts as in lick form, its presence in the faeces will prevent the development of the eggs.

Copper kills wireworms and the large stomach worm. Nicotine kills a good percentage of the small intestinal worms, also tapeworms.

Arsenic as sodium arsenite has been widely used in South Africa along with copper sulphate as a remedy for the large stomach worm. •As it is highly poisonous and requires careful handling, and does not appear to be more effective than copper sulphate alone against this worm, its use is not recommended.

Whether lambs intended for the works should be dosed more than once would depend on several factors: how soon you are able to get them away, degree of infection of pastures, nature of season, convenience of handling, etc.

Nicotine and Bluestone Drenches

Where you can quit your lambs off the mother in December or January, one or at most two drenches should be enough. If you hold them till on in February, and have good facilities to handle and drench, and particularly in a wet season, it is advisable to follow a programme of drenching every three weeks from Christmas on. You could check results for yourself' by marking and leaving undrenched a percentage of average lambs. The following is a recommended dosage table for bluestone-nicotine drench:— 2 per cent: Dissolve 16oz. bluestone in 5 gallons of water, and add 16 fluid ounces of 40 per cent, commercial nicotine sulphate. 4 per cent.: Same quantities of bluestone and nicotine, 2| gallons of water. 5 per cent.: Same quantities of bluestone and nicotine, 2 gallons of water.

DOSAGE.

2 per 4 per 5 per cent. cent. cent. Adults .. .. 2oz. loz. (30 c.c.) 20 c.c. Two-tooths .. Ijoz. |oz. (25 c.c.) 15 c.c. Lambs, 8-12 months loz. Joz. (15 c.c.) 10 c.c. Lambs, 4-8 months |oz. goz. (10 c.c.) 8 c.c. Lambs under 4 mths. soz. |oz. (8 c.c.) 5 c.c.

A WARNING:—Where lambs are weak, draft them off and give them the next dose lowest down, according to age, and repeat it in ten days; otherwise, with a full dose, they may die.

Applicants for Entry to Flock House Farm FROM time to time vacancies for trainees occur at the Department of Agriculture’s Flock House farm of instruction at Bulls, and intending applicants are advised to apply promptly to the Director of the Fields Division, Department of Agriculture, Box 3004, Wellington, for full particulars. Training, which is free, is open to boys of from 14j to 18 years of age.

The general aim is to give an initial training in all branches of farming, make a boy self-reliant, instil a sense of responsibility, and give him a favourable outlook on farm life. The term is for 12 months, and applicants may enter at any time of the year. The following weekly remuneration is paid to boys at Flock House: —

Held in Savings Account First 3 months 2s. 6d. Is. 6d. Second 3 months ss. 3s. 6d. Third 3 months 10s. Bs. Fourth 3 months 17s. 6d. 14s. 6d.