Drains and Irrigation
THIS chapter will discuss how water conservation drains aredesigned and used to fill the keyline dam described in Chapter XVIII. This projectis now to be completed to the stage of watering and the managing of irrigation land.
The line of the water conservation drain may have been peggedprior to the construction of the dam during the marking out or site preparation.The keyline dam water conservation drain starts from water level at the overflowpoint of the spillway, which is on the line of the centre of the wall. Preferablya line is pegged rising at 0.5% right round the dam in the direction of the generalrise of the country. (N.B. The spillway is usually on the downland side of a keylinedam.) Where the land shape has smooth contours, pegs 50 feet apart may be suitablefor the construction of a drain, but it is preferable that Pegs be placed at closerintervals around the inside bends of valleys or the outside curves of ridges. Whena peg intermediate between two 50-feet pegs is to be placed, it is not necessaryto level in the peg 1-1/2-inch fall in 25 feet. The intermediate peg can take itsheight from the last preceding level.
The section of a water conservation drain provides that thecentre line of the drain bank is over the pegs. The pegs, when placed, representthe centre line of the embankment of the drain, so that when digging commences inthe construction of the drain, earth is moved from a line some feet above the pegs,so that the centre line of the finished bank will coincide with the pegs.
Various implements can be used for the construction of the drain,from 3-point linkage attached-farm-graders through to the angle-blade large bulldozer.If a farm implement is to be used, a chisel plow should first cultivate the areaabove and below the pegs, and by just missing the line of pegs and leave them undisturbed.From two to four runs of the plow may be necessary, according to the size of thedrain. The plowing of the land below the pegs assists the bonding of the subsequentbank material.
A single deep rip furrow made with a small tractor, travellingso that the downhill wheels leave the pegs undisturbed, is a further aid to the constructionof the drain with the smaller type of equipment. The farm grader can then be operated,digging the earth from a regular distance above the pegs and throwing it towardsthe pegs; in this way half a dozen or more runs may be necessary to form the drain,including its bank. Throughout the operation the pegs should be preserved in theirtrue position. Pegs are preferably about two feet high.
The size of the drain depends on the slope of the country andthe amount of catchment area above the drain. The conservation drain section illustratedis the one I generally employ for our own keyline dams. Its capacity range is upwardof 350,000 gallons per hour. (See Fig. 13, Chapter XVIII ).
There is a tendency for all equipment to "pull down"on the inside curve when the implement is travelling around a valley, and to do theopposite, i.e., climb-up when the implement travels on the outside curve around ahill or ridge. It is convenient and good practice to put in marker pegs one footto three feet above the line-pegs in the valleys to compensate for this tendencyto pull down. After the first couple of runs with the implement the obvious correctionscan be made. Similarly, but in a reverse manner, compensation is provided againstthe tendency of equipment to climb on the outside curve of a ridge.
An angling bulldozer (angle 'dozer) provides a very efficientimplement for constructing water conservation drains. The angle 'dozer should beoperated with the heel of the blade against the lower or downhill track of the tractor,and working in such a manner that the lower track is in the cut of the drain as itis formed and the uphill track above the cut. The pushing forward and sideways ofthe earth with the angle blade tends then to throw the rear of the tractor uphill,but the weight of the tractor compensates for this and permits highspeed accuratedrain construction. Again, some allowances must be made for a tendency to move downhillon the inside curve around a valley and to move uphill on the outside curve rounda hill or a ridge. The line of the cut of the drain is again uphill from the lineof pegs, the first pass being made in such a manner that the earth from the bladefalls on the uphill side of the peg.
The angle 'dozer operating this way works like a giant mouldboardand can be operated efficiently by maintaining as big a bite as the tractor willcut and push evenly in second gear. It is advisable for a man to walk ahead of thetractor with a 6-foot pole, which he holds on the line peg and ahead of the 'dozer,so that the operator can see his line of travel clearly. The operator on his owncannot sight the pegs of the line quickly enough to maintain the generally smootheven curves that are desirable in these drains.
After the first run the full length of the drain, the tractormakes another pass. The tilt of the angle blade needs to be readjusted, so that itcuts a drain to its pre-determined shape. Two rapid passes will often shift sufficientearth to form the drain illustrated by the section diagram, but in harder conditionsthree or four passes may be necessary. Feeder drain sections, notably the shorter-lengthdrains (under 900 feet), when newly constructed, are a flat V section with the uphillline and the bottom point of the V represented by the cut of the angle blade andthe downhill shape of the V represented by the slope from the deep point of the drainto the centre line of the earth bank and the pegged line.
For longer drains with larger capacities, their section is representedby a flat centre section of the drain equal to the width of a 'dozer blade, a longsloping uphill cut on the topside, a long slope to the centre or high point of thebank on the downhill side to the pegged line, and a further earth slope behind thebank. Where the length of a feeder drain exceeds 900 feet, it requires theoreticallya progressively larger section of drain to carry the quantity of water which in effectincreases throughout its length from its beginning through to the dam. This can beachieved by constructing the drain from the end near the dam, and after completingthe necessary number of runs to form the drain to the section required at the endaway from the dam, make two more runs from the dam-the first one travelling three-quartersof the distance of the drain and the last run half the distance of the drain fromthe dam end. This provides a larger section of drain where the water flow will begreater. One extra run in a drain considerably increases its carrying capacity. (SeePictorial Section.)
Water carrying capacity, increasing as the length of the drainincreases, may also be affected by planning the feeder drain with increasing ratesof fall towards the dam. A steeper rate of fall is therefore to be made in the sectionnear the dam and the flatter fall in the end section furthest from the dam. However,the drain of uniform fall, but increasing in size, if necessary, as it approachesthe dam, is the type preferred.
The angle 'dozer constructed drain, while being the cheapestand fastest method I have employed, leaves the bank somewhat lumpy and uneven. Farmequipment can then finish off the drain quite smoothly. The upper wheel of a farmwheel-tractor with an attached chisel plow is placed in the bottom of the drain withthe downhill wheel on the drain bank. One light run with the implement will smoothoff the shape of the bank. A farm tractor and attached grader can also be used totrim up both the inside and outside of the drain bank.
As soon as the water conservation drain is completed, the hard,newly-cut surfaces should be cultivated to a depth of 2-1/2 inches or three incheswith the tractor and implement and working on its first run with the downhill tractorwheel in the bottom of the drain and its upper wheel higher on the cut section ofthe drain. The whole area of the drain is cultivated once and parallel with the drain.The drain should be immediately sown down to the usual pasture mixture, togetherwith an application of fertiliser.
It is desirable in the interests of the efficiency of the drainand the working of the property to have the pasture in the drain area of as goodor better quality than the rest of the paddock, so that stock will keep this areaeaten off. To this end, it may be as well to double the application rate of superphosphateon the soil of the drain area which, after all, by virtue of the topsoil being removed,may be very poor.
The feeder drain is designed as above, commencing from the ccntreof the spillway at the centre line of the wall, so that complete control over watercan be exercised at all times. For instance, with the drain starting from this pointand rising steadily right around the water line of the dam, the drain is above theend of the wall at the opposite end from its starting point. There is no interferencewith the wall. With the drain in this position, water can be let into the dam fromany part of it around the dam. If there is an eroded area within the top water lineof the dam, run-off water can be flowed into the dam over another area, avoidingthe eroded area altogether. In order to by-pass water over the safe area into thedam it is only necessary to block the drain at the desired place and trim its bankfor a short distance.
If required, run-off water can be by-passed right around thedam into the spillway and on to the water conservation drain or catchment area ofanother dam. If the overall plan envisages the maximum possible conservation of allrun-off water no other design which embodies a different association of the feederdrain and dam to this layout will serve as efficiently or be as satisfactory.
A feeder drain should never be constructed to discharge waterdirectly into the dam near the wall, although this has been the procedure on thefarm dams where feeder drains are used other than those of our own design.
In Keyline there are usually only two drains down the land slope,one being the feeder or water conservation drain now discussed, and the other theirrigation drain. Heavy run-off water can pass over an irrigation drain without damage,so that there is no vital necessity that a feeder drain be constructed to such sizeand in such a manner that it never fails to hold and transport all the water thatruns into it. If a feeder drain is sufficient for its purpose of filling the dam,but not large enough to transport the largest flood rains, then it is desirable thatthe area where water will overtop the drain should be deliberately located. A slightlylower bank produced by levelling off by hand on a suitable ridge section which hasbeen Keyline pattern-cultivated provides a perfect safety against the heavy floodrain. The maximum amount of control should always be exercised over water on thefarm.
Marking Irrigation Drain: The purpose of the irrigationdrain is to transport water from the outlet valve along the higher boundary of anirrigation area. Marking out or levelling in with a level should commence at thevalve.
A fall or grade similar to that employed for the feeder drainis suitable where the land is not too flat. In our own irrigation drains we generallyprovide a steeper fall (up to 1% grade) for the first 50 feet of drain from the lockpipein order to counter an occasional tendency for a wet area to form near the outlet.
A high degree of accuracy in the construction of a feeder drainis desirable, so intermediate levelling pegs as close as 12 feet 6 inches or lessapart may be placed to preserve the generally even-curved line of the drain.
On even-shaped land this procedure imparts perfect curved shapesto the drain and preserves a very desirable accuracy of line in the finished drain.As water is to flow over the edge of the irrigation drain for distances of up to50 feet, some effort should be made to get considerable accuracy in the layout ofan irrigation drain.
Constructing Irrigation Drain: The irrigation drain servesa totally different purpose to the feeder drain, and it is of different design andconstruction. It is designed (in undulating country) so that water flows within theexcavated drain entirely, and no assistance being provided by a bank formed fromthe excavated material, as in the feeder drain. (In flatter country the design maybe different.)
The irrigation drain is constructed with the lower edge of theexcavated drain on the line of the levelled marker pegs, so that the water it transports,on being blocked in the drain with the blocks, spills over solid unexcavated material.Preferably the drain should be constructed with the excavated material thrown uphillto be spread out there, but in practice there is no farm equipment that will do thisoperation properly. On land with any slope, earth does not throw uphill readily,and the construction of an irrigation drain inevitably requires some hand work. (SeeFig. 13, Chapter XVIII.)
There is no suitable implement that will construct an irrigationdrain to the desired sections in country of different slopes. An implement couldbe made that would be suitable for certain slopes of land, but its range of useswould probably be very limited. However, it is suggested that the drain be constructedwith the use of one or more implements such as a delver, ridger, lister, or evena large single furrow plow. The first run with a farm tractor and any of the aboveimplements should be made in such a way that the ground broken by the implement shouldnot extend downhill to the pegs. Some implements will throw a measure of earth uphill,but there will always be a spill of earth onto the lower side of the drain which,if only a small amount, can be levelled off there by spreading, or preferably thrownuphill to the top side of the drain by hand shovel work.
The implement used should break the ground above the pegs andwithin the finished section size of the drain. When the soil is broken to the desireddepth and a little under the finished width, the drain can best be finished by handshovel operation by spreading the loose earth uphill and preserving the exact widthand depth of the drain throughout and working in such a way that the pegs are stillin position and an inch or two from the lower edge of the drain when this is completed.As soon as the drain is completed a small quantity of water should be let into itfrom the outlet valve of the dam to check the drain. The final finishing can thenbe done very accurately. Another larger flow of water could then be turned on fora short time as a final check.
Irrigation: When irrigating from the dam and employingKeyline flow methods, the water is first turned on at the outlet valve and allowedto flow to the end of the drain on the downland limit of the irrigation area. A blockmade of sheet metal or earth or any other suitable material is placed in the drainat this point, and by blocking the water, ponds it back and forces it to spill overthe lower lip of the drain and run down over the land.
(NOTE: After irrigating, the drain stops are placed at intervalsalong the drain, so as to distribute any run-off rainfall.)
In order to preserve the correct water spread, proper time ofcomplete wetting and for continuous soil and pasture improvement of the paddock wehave employed certain specified procedures.
Pattern Plowing of Areas: The even spread of water isobtained by the pattern impressed on the land by the design of the appropriate keylinecultivation.
Keyline cultivation is simply cultivation with a chisel plowwhich parallels a selected contour line in such a way that when the parallel cultivationinevitably moves off the contour, the furrows oppose the natural flow pattern ofthe run-off water. The irrigation water then spreads evenly over the surface. Themain art in keyline cultivation, when it is used in this manner as a positive controlfor the spread of irrigation water, lies in an understanding of the actual contourshape of the irrigation area, and in being able to select the line which is to guidethe parallel cultivation, and then to determine the correct paralleling of this line,whether above or below it.
While this is simple enough in its cause and effect, it is notalways at the outset fully understood to the extent that an inexperienced landmancan put it into operation effectively on his own without first studying the landshape. He can, however, by the following procedure, illustrate the contour shapeof the area and so determine the methods which will control the irrigation watereffectively. The contour shape of an irrigation paddock can be determined and transferredto paper in the following manner: First, a line is drawn on a sheet of paper representingthe approximate curve of the irrigation drain. Next, in the paddock, step a distancefrom the centre point of the irrigation drain and downhill at right angles from itabout 90 feet and place a peg. From this peg run a true contour line in both directionswith a levelling instrument, placing pegs at 50-feet intervals across the irrigationarea. Next, place another peg 90 feet downhill at right angles to this contour lineand peg another contour in the same manner as before. Measure and mark on the paperthe distance of the two contour lines below the irrigation drain, marking first thedistance stepped or measured at right angles from the irrigation drain to the twocontour lines below. Then about three distances from the irrigation drain to thefirst and second contour line and each side of the centre are measured and markedin on the paper. These measurements are taken from even distances along the drainline (at right angles to the drain) to the first contour; and again at right anglesto the first contour down to the second contour and marked in on the sketch. Thecontour shape of the area is disclosed by joining the points to form the two contoursbelow the drain, and the appropriate guide for the cultivation can be selected.
The irrigation area watered from the dam should quicklybecome of high productive value, so it should be suitably fenced. If the area isalready carrying a good pasture, it would be as well to feed it off quickly, andthen, if the weather is dry and the land likewise, cultivate to the particular patternwhich was selected.
Cultivation Procedure: The cultivation depth should becarefully determined beforehand by the following means: The soil is examined witha spade to determine the depth where, by the appearance and smell, the soil couldbe considered to be in reasonable condition, namely, fertile. It may be only oneinch deep and will rarely be more than 2-1/2 inches. If it is the minimum of oneinch and the pasture is fairly tight, a cultivation should not be more than two inchesdeep. Such cultivation need not disturb much of the pasture.
The first watering of a new area is preferably given in themorning, so that, with the mistakes and delays that may occur, the irrigating canbe at least completed on the day it is started. In watering, certain relevant detailshave to be determined, and, first of all, is the width of the strip of land belowthe irrigation drain. This width should be narrow enough to enable a full flow ofwater from each overflow position on the drain to extend across 90% of the distancewithin a period of one hour. The reason is simply that land thoroughly immersed orsaturated in water for any period of time longer than one hour may suffer "drowning".The beneficial soil life, which, after all, produces the various factors which wecall fertility in soil, require oxygen. The whole complex of this life can be seriouslydisturbed and changed if water is continuously left too long flowing over land. Theideal length of time is somewhat less than one hour.
Irrigation is designed to produce abundant pastures or cropsin the best seasons as well as the worst of seasons, and this is the basis or thereason for its use. However, fertile soil will produce more under irrigation conditionsthan infertile soil, and it is a deliberate function of irrigation to control waterand air in relation to warmth in such a way that the fertility of any soil, fertileor otherwise, is rapidly increased. An inch of fertile soil under controlled irrigationconditions as in Keyline, can be converted into a foot or more of depth in two seasonsof irrigation. This depth and degree of fertility can not only be maintained butincreased.
Irrigation of the new area is accomplished in the followingmanner. The valve at the dam is opened and the water is allowed to flow to the farend of the irrigation drain. Here the first drain block has been placed. The drainblock or dam may be a piece of sheet metal cut to the shape of the drain and pushedinto the earth. A few shovelfuls of soil on the water side of the block may be necessaryin order to make the block effective. The water thus held back overflows the lowerlip of the drain and spreads down the slope of the irrigation paddock. Before theforemost edge of the flowing water reaches the lower limit of the paddock a seconddrain block is placed to spill the water again at a new site fifty to one hundredand fifty feet away and towards the dam. The distance from the first block to thesecond may be gauged approximately as 2-1/2 times the distance to which the waterof the first block has spread laterally from the overflow position. Irrigation continuesuntil the end of the area nearest the dam is watered and the watering is completed.
The first irrigation of a new area should provide the informationfor future watering procedures. The length of time that it takes flow water to reachthe lower side of the irrigation paddock is determined and it should be less thanone hour. Later irrigation of the area would simply mean that the farmer controllingthe watering would come back to the area every half to one hour period, accordingto this time of flow, and with experience after a few waterings it is a simple matterfor one man to control three or four dams contained in an area of, say, 600 acres.
On good, even-shaped land we have found that the first wateringgenerally produces a good distribution, but on occasions there will be small areasunirrigated. The paddock should be examined twenty-four hours after watering to determinethe effectiveness of the spread, and unless sizeable areas have been missed, it wouldbe unnecessary to especially irrigate a dry area. Thirty-six hours after wateringthe condition of the land should be such that all is moist but none is wet and noneis dry. Dry spots should be marked and studied in relation to drain block positions,so that on the following watering more effective spread would be secured.
Not all land takes water in the same way, because the shapesall differ, even a little, and the shape of the land and the cultivation patternare the controlling factors. A good spread of water does not at first occur wherethe land is without a sufficiently uniform contour shape. Small local depressionsor rises that are unrelated to the general shape of the land can cause too much moisturein the hollows and too little moisture on the rises. A corrected plowing patterndetermined on inspection may be the suitable answer. On other occasions, the nonuniformareas may be too small in size to enable a plowing change to be implemented, sincethe distance of movement and change of movement in the plowing may be too short tobe practical. In this case, "border checks" can be used to direct waterto the awkward spot.
Border checks are one of the means of controlling water in flatter-land,flood-irrigation systems usually associated with the large irrigation areas. Generallywith this method water is carried along the higher border of the irrigation country,which may be very flat, and water flows from the irrigation drain through variousoutlets along the length of the drain. The uniform spread of the water over the countryis controlled by the border checks, which are small banks of earth 18 to 24 incheswide by as little as three inches high, which are thrown up by a "crowder"at right angles to the drain. The border checks parallel each other down the slightslope of the land at intervals of about 30 feet and provide an efficient means ofspreading water uniformly over the land. It is sometimes called border strip irrigation.This check or bank is used where necessary in Keyline pattern irrigation to takewater to the unwatered area, but whereas in conventional border check or border bankor strip irrigation numerous border checks are used, one to three banks is all thatis likely on a reasonably-sized irrigation paddock in Keyline pattern irrigation.However, a study of the pattern of water movement and of areas not watered 24 hoursafter watering ceases will indicate quite clearly whether one or two border checkswill assist the even distribution of water.
"Crowders" are the regular implements used for constructingborder checks and consist essentially of two blades six feet long similar to thoseon small graders. They are arranged in an open V with the forward ends of the bladessix feet apart and the rear end of the two blades around about two feet apart. Theblades have various means of control, and, by travelling forward over land that hasbeen lightly cultivated, in one run crowd sufficient material from the wide openend of the blades to the narrower end to form a satisfactory small bank without leavinga notable depression in the areas from whence the soil is taken. The same effectcan be achieved quite satisfactorily in two runs with a small farm grader.
Distance of Water Flow in Irrigation: In consideringthe distance of water flow, it must be realised that soil will change by developingimproved fertility and structure under good irrigation conditions and will be changedby deterioration if the soil is not managed properly during increased water application.Clay soils may allow water to flow at the first irrigation a relatively long distancerapidly. With the improvement in soil fertility due to well-managed irrigation, thedistance water will flow then may be considerably reduced.
Soils that are poor and porous, such as some low-quality loamsor sandstone soils and some granitic soils, will, by seepage, limit the distanceof water flow in the hour, but with rapid fertility improvement the distance willincrease. Where circumstances permit, it is preferable that the water for the irrigationarea be supplied by the one drain, and that the distance downhill across the irrigationarea be limited to a distance that water will travel within an hour, and at the sametime provide a strip of unirrigated land below the irrigation paddock, and at leastas wide as the irrigation country itself. This strip lies between the irrigationarea and the valley below. For instance, if a dam provides sufficient water for thefull irrigation of ten acres of land, it is preferable that the shape of the landbe rectangular along the irrigation drain; 14 chains long by 7 chains wide, insteadof square, 10 chains by 10 chains.
Where, by the shape of the land, such arrangement is not possibleand a square block has to be irrigated, then watering could be by two drains, oneat the top of the irrigation paddock and one across the centre, both falling in thesame direction at the same rate of fall. The irrigation procedure then would be tocommence at the end of the top drain away from the dam and watering the top stripprogressively back towards the dam, and then by flowing the water over a speciallyprepared path, as between two border checks, allow the whole of the water to runinto the second drain and complete this area by watering from the end of this drainaway from the dam, and proceeding, as usual, back towards the dam.
Management of the Soil in Irrigation Land: The treatmentthat a soil may need varies widely according to the present state of developmentof the soil and to weather conditions. There is no exact theoretical method of determiningthe water requirements of a particular soil that will equal the practical examinationof soils on the spot by the farmer with a spade. Many factors affect the developmentand fertility of the soil, but probably the overpowering influence is that of soilclimate. The aim is always to provide the best condition of moisture, warmth andair in the soil for soil life and plant growth.
An examination by the farmer of the soil in an irrigation paddockis made by digging a spit of soil with a spade to the full depth where any pastureroot penetrates.
Examination takes place by the look and feel of the soil todetermine whether it is friable and crumbly with the unmistakable appearance of fertilesoil. The fertility or otherwise is checked by the smell of the soil. Almost everyone,even without experience, knows the typical delightful smell of fertile soil. Belowthe zone of fertility determined on these lines, which may be only an inch or two,the soil will appear either close and compacted in clay soils, or loose, clean andsandy in light soils. The top zone of compacted soils is apparent to the eye andfeel, and usually has no smell whatsoever. It could be called the neutral zone. Belowthis zone, there will be a change in the soil again, obvious both through sight andfeel, and there may be on occasions a very definite change of smell to sour and perhapsobjectionable.
The best means of improving soil is the right type of cultivationat the right time. Cultivation with a chisel plow and on the pattern decided forthe irrigation area, should be undertaken when, from this examination, the soil needsit. The soil of the irrigation area should be closer to its drier condition thanto a good moist condition. Cultivation can be best undertaken immediately stock hasmoved off the area. In warm weather irrigation is done on the following day. Cultivationtime and depth should always be decided strictly on the condition of the soil atthe time. Penetration that is too shallow will usually do some good, but a depthof penetration that is much too deep provides only the minimum benefit from the maximumwater application. The penetration should just exceed the main pasture root zoneand enter the neutral zone of the soil. With a soil in dryish condition, the resultantcracking coupled with the correct depth of penetration provides the air requirementsand the space for the continued development of the soil without waste of water. Withexperience, cultivation can be used to control very precisely the amount of irrigationwater taken in by the soil.
The response of the pasture and the soil to this planned procedurewill be that the major root zone will deepen and at the same time, where warmth conditionsare suitable, a rapid development or even a climax of development of soil life takesplace by the provision of well nigh perfect living conditions for that life. Thesegood living conditions, extending, as they do, just through the maximum root zone,allow the soil life to develop rapidly from the abundance of its food, the best foodof all, the dead roots of pastures.
The improved conditions in the soil, both for soil life andpasture growth, continued for a period of only a few weeks, will, on examinationagain by the farmer with his spade, disclose that a rapid development of the depthand quality of fertility has taken place.
On clay or heavy soils resulting from the break-down of mudstones,slates, schists, etc., experiments in the cultivation of irrigation land have beenconducted on our own properties six times during the warm and hot weather, with aresultant continuous improvement in soil development and pasture growth.
It is not known how many cultivations a pasture in this typeof soil, coupled with good irrigation, will stand during, say, the hottest sevenmonths of the year before the cultivations end in a detrimental way by destroyingtoo many pasture plants, or in other ways by restricting soil development. Obviously,there is a stage where too much tillage would be damaging, even under the best irrigationprocedures.
It is suggested that. the pasture soil be examined by inspectionwith a spade every month during the first year of irrigation, and that cultivationduring this first year be as frequent as is indicated by the condition of the soil.
Of the two types of soil, heavy and light, the depth of cultivationis somewhat more critical in the light sandy soil, and, as a general rule, the cultivationdepth of these soils should only be allowed to penetrate just enough through themajor root zone. The factors of cultivation are again more critical during the firstyear of irrigation. During the second year, the irrigated land will be totally differentfrom the original soil. It will then hold a condition of better balance than previouslyof the factors of moisture, warmth and air. It will require less treatment for itscontinued development. Earthworms will have come in, whether they were previouslyapparent or not. The earthworm life should develop rapidly and probably by the endof the second year of irrigation the depth of fertility and the structure of thesoil may be such that it will look after itself, continuing its further developmentautomatically.
While it is quite certain that this rapid soil development withits consequent beneficial effect on pasture and stock does take place in this mannerin a short time, it is not certain yet how long the fertilty developed in a yearor two will continue to improve without further work (keyline cultivation) or whetheror when this process will stop and a decline set in.
On "Nevallan", our experiment farm at North Richmond,we had country of very varied earth types. In one part it ranged from the shallowestgrey soil through to yellow clay subsoil; others from yellow subsoil to soft yellowshales, even to medium hard blue shale, and all to be seen on the surface. Therewere other areas of sandy soil, with places where the sand was dean enough, and weused it in cement work for our buildings. On all these earths and under natural rainfallconditions, eight inches of highly fertile soil had developed in three years of Keylinetreatment. During the next two years, the depth of this fertile soil had increasedto two feet, with the roots of the pasture grasses well in evidence at that depth.Some green growth was continuous through the recent drought, the worst since 1944.A dramatic soil development during the fourth and fifth years had taken place naturallyfrom the fertility that had been developed through the first three years of Keylinework.
How long this process, which increases the fertility and extendsthe depth of the fertile soil, will continue is not known. The ability of the developedsoil to look after itself has been shown by the fact that it was apparently unaffectedby the long-term saturation of the soil which extended from early in 1956 right throughto the winter months, and by the fact that during the drought referred to it wasable to maintain a green growth of grass where no other neighbouring rain pasturecould. The earthworm population, which became apparent for the first time in March,1954, has developed rapidly in numbers and size. Earthworms larger than those everseen in the district can be obtained in every shovelful of earth during the castingseasons for earthworms when the moisture conditions are suitable.
These facts indicate that the state of the soil should be watchedcontinuously even after the second year of irrigation, and if there is any fallingaway of condition, as evidenced by compaction, loss of structure, or the absenceof a noticeable increase in the earthworm population over the previous year, or evidencethat the neutral zone (zone of no smell) is higher, then keyline cultivation shouldagain be introduced.
Cultivation of the soil in its condition after two years ofdevelopment by irrigation and keyline cultivation will be a different matter to thecultivation of the first year. It will now be practically impossible to cultivatetoo deeply, because of the depth of the developed soil. From then on the soil canbe worked, when cultivation is needed, to as deep as the logical maximum that issuitable to the chisel plow and the particular farm tractor, with, however, the effectkept in mind that it will have on irrigation water.
Experiments have shown that as progressively deeper cultivationis followed in the first year of irrigation, the improved structure and fertilityof the soil develops beyond the depth of the work. It is therefore not necessaryfor cultivation towards the end of the second year to reach the full depth of thenew soil.
The recompaction of a fertile soil that has been developed bythese methods if and when it does take place, affects only a limited depth from thesurface. Compaction does not seem to take place below five inches. A cultivationmaximum depth of five or six inches may be all that is necessary to treat quite effectivelya depth of 24 inches of developed soil.
Sowing Seed into Irrigation Areas: On occasions it maybecome advisable or desirable to introduce new species of grasses into an irrigationarea. Sowing should be done as accurately as possible and the condition of the groundis preferably just moist or even slightly drier than would be considered good sowingconditions. The area may then be watered immediately and closed up for about twoweeks before stock are brought in.
The reader having come so far will appreciate that the methodsand procedures discussed above are not those now in general application for the managementof irrigation pasture. Official recommendations do not cover the Keyline cultivationpattern as a control for water distribution. Continuous year-by-year applicationsof artificial fertilisers, and particularly on irrigated pasture, is the usual orthodoxview. It is quite clear that the controlled application of water, plus artificialfertilisers, plus lime on occasions, will produce lush and abundant pasture growthwith high carrying capacities. The assumption, which I do not accept, is that theimportant factor is to keep the top inch of the soil in a good pasture-growing moisturecondition and replace the loss of nutrients from this thin band of soil by regularapplications of the appropriate artificial fertiliser. It is assumed that, in general,phosphates are deficient in soils and need to be replaced by regular applicationsof superphosphate. Continuous application of water under these conditions inducessoil deficiencies of other mineral elements of fertility, which have then to be addedartificially on appropriate occasions.
The Keyline methods, however, assume generally that there areadequate minerals of all varieties present in the soil, but not necessarily in availableforms or states, and it is good practice to make the unavailable minerals (phosphatesgenerally being the critical one) available immediately by an appropriate applicationof superphosphate at the start of the development of the soil of an irrigation area.However, the rapid climax development of soil life due to the improved conditionof the soil climate act on the existing but unavailable minerals and breaks themdown rapidly into forms readily available to plant life. Chemicals, such as superphosphate,are, with advantage, used once or twice in the initial stages of soil development.Their purpose in Keyline is to provide rapid development of pasture root growth aswell as pasture, so that -a basic food of soil life, dead roots of grasses, is inabundant supply as soon as possible. The continuous development of soil by the maintenanceof the best possible soil climate right through to the depth of the zone of maximumroot development during the first two seasons, continuously and progressively makesavailable the mineral elements of fertility and processed to their most perfect formby the natural factors operating on them. The effect is that in irrigation in Keylinethe pasture is soon produced from some feet depth of fertile soil instead of froman inch or two of a very artificial growth medium.
I have proved, to my own satisfaction, that this conceptionof soil and pasture development, now commended to others, is a satisfactory and practicalone.