Topdressing Cobalt-deficient Land from the Air

New Zealand Journal of Agriculture, Volume 75, Issue 5, 15 November 1947, Page 501

Topdressing Cobalt-deficient Land from the Air

By

E. D. ANDREWS,

Animal Research Station,

Wallaceville, and A. M. PRICHARD, Aerodrome Services, Public Works Department, Wellington.

USH sickness, - a stock ailment affecting ruminants, -U occurs on lands deficient in cobalt. 7 The disease can be cured and prevented by supplying cobalt to the animals, the most effective method being to increase the cobalt content of the herbage by topdressing with cobalt salts. Topdressing bush-sick lands with cobaltised superphosphate has now become common practice, providing a cheap, effective, and simple means of improving the cobalt status of pasture and controlling the disease. That method is readly applicable to flat lands where machinery can be employed, and hand topdressing has been resorted to on some of the steeper country, but there still remain the inaccessible blocks of land and broken hill country to which the application of fertilisers has so far proved impracticable. However, cobalt must be supplied to the stock and means

other than topdressing the pasture have hitherto been employed, though none is as effective. The use of aircraft to distribute a cobalt fertiliser would avoid the difficulties imposed by inaccessibility and broken terrain, and the successful and economic employment of such a means forms the subject of this article. An article in the “Journal of Agriculture” for February, 1945, by one of the present writers (A. M. Prichard) described the successful sowing of lupin seed by air on sand dunes of the Ninety-Mile Beach. More recently, the late O. J. C. Anderson, Aerodrome Services, Public Works Department, Wellington, and I. J. Cunningham, Superintendent of the Animal Research Station, Wallaceville, reported in the “Journal” for September, 1946, an experimental aerial topdressing of bluestone on 1100 acres of flat, copper-deficient peat land. The background of experience gained from those trials

proved of great value in the planning and execution of the present experiment, but fresh. problems had to be faced. The previous experiments were carried out over flat country; in the present instance the main object was to topdress country essentially hilly. That introduced extra flying hazards, and one of the purposes of the experiment was to establish a technique designed to reduce hazards to a minimum while ensuring a satisfactory distribution of material.

While the choice of a suitable area for topdressing was under investigation a request was received by the Department of Agriculture from Mr. K. M. Hickson, Waimiha, that consideration be given to the possibility of aerially topdressing his property with cobalt. This farm, 23 miles north of Taumarunui, is 2760 acres in extent, of which 1800 acres is in pasture, 200 acres in scattered manuka, and the rest in thick manuka or native bush.

Features of the Farm

Inspection of the farm showed the following features:—

1. It is within the cobalt-deficient pumice area of the King Country.

2. It has a previous history of stock unthriftiness and mortality.

3. Access to the farm is difficult. Supplies are brought in either by pack horse over rough country for three miles or along a disused bushtram track for about the same distance. In good weather the tram track is negotiable by a small farm truck as far as the homestead.

4. The country is mainly hilly, with a few steep faces and deep gullies, but has sufficient easy rolling and flat country to offer varied experience in the technique of aerial spreading.

5. Because of the difficulty of access and the nature of the country, normal topdressing procedures have not been feasible.

6. A temporary airfield about 3| miles from the homestead could be made available on the Native Development Scheme Block at Waimiha. The cobalt-deficient nature of the farm having been confirmed by analyses of pasture samples from all the main areas, it was planned to topdress aerially at the rate of 20oz. of commercial cobalt sulphate to the acre. That figure was chosen because previous experiments had indicated that such a rate of application gave protection against bush sickness for proportionately longer than the lower rates of soz. and lOoz. to the acre. In the plan on page 504 farm boundaries are indicated by broken lines and areas topdressed by heavy lines. For reference purposes it was more convenient in practice to use aerial photomaps of the farm with boundaries and areas similarly delineated. Each area contained a multiple of 60 acres, which was the area estimated to be covered by one plane load of material. As far as possible, each area was bounded by straight or regularly-curving lines to facilitate the planning and execution of aerial spreading technique.. In that manner nearly all the pasture land, with some of the encroaching land in scattered manuka, was included. The total extent of the areas was 1800 acres. Advantages of Liquid The question arose whether it was preferable to spread cobalt sulphate in solid form or as a solution. Preliminary laboratory tests had established that a saturated solution of cobalt sulphate would not corrode any metal fittings and fabrics used in the aircraft. The use of a solution would mean that water as a diluent would represent “dead” weight in the pay load, but a liquid would . have the following advantages:—

1. Liquids can be readily loaded into an aircraft by a gravity system or by pumping. 2. Granular solids tend to pack under the influence of aircraft vibration, causing irregular discharge rates. The use of a liquid ensures a smooth discharge. 3. Solids must be discharged vertically, or nearly vertically, below the container, but liquids can be piped to any part of .the aircraft, allowing suitable discharge points to be chosen for maximum effective spread. / 4. The maximum load can be carried only over the centre of gravity of the aircraft, which with a solid would necessitate cutting a hole for the installation of discharge equipment in the most highly-stressed part of the aircraft. -As that is not feasible, it would be necessary to locate the load and discharge orifice to the rear of the centre of gravity, upsetting the trim and balance of the aircraft and reducing the load. With liquids the centre of gravity of the container system can be located over the centre of gravity of the aircraft, enabling the maximum authorised weight to be carried. For those reasons it was , decided to employ cobalt sulphate in the form of a solution. . In the aircraft used the maximum weight of solid cobalt sulphate which could have been carried was 901 b.; by using cobalt sulphate solution 3101 b., containing 1161 b. of cobalt sulphate, could have been carried. Because of the rather uneven nature of the field from which flying was undertaken, the load was reduced to 2001 b. of solution, containing 751 b. of cobalt sulphate, to provide a wide safety margin. Aircraft and Fittings The aircraft available was a Whitney Straight side-by-side two-place

monoplane. Examination showed that removal of the passenger’s seat afforded an ideal mounting place for a single tank of adequate capacity. The dimensions of the tank were 18in. diameter by 28in. long lying fore and aft on its side. The tank was fabricated from 28-gauge tin plate with spot-welded and soldered seams, ends, and baffles. Clear lacquer was floated on to all interior surfaces to prevent rust, but that treatment did not withstand hot solution and peeled off in large sheets. A large, airtight filler- cap, which also provided an inspection port, was fitted to the , top, and a vent pipe forward, opening in, the region of maximum pressure below the main plane, was brought up through the tank to provide pressure and so minimise the effect of change of head as the tank emptied. The control valve, 2in. in diameter, was taken right through the tank in a similar . manner to the vent. When closed it is sealed by a rubber washer expanded outward by pressure between two cramping plates, forming in effect a thin piston. 1 Ports in the wall of the tubular valve are uncovered as the piston is raised. A smaller extension of . the valve tube proper has a similar rubber piston seal to prevent splash and leakage even if the aircraft becomes inverted. Liquid is taken from the" bottom of the valve through the floor in a 2in. rubber hose to' absorb random vibrations between the tank and the aircraft floor. Beneath the floor the rubber hose is attached to a short

vertical pipe closed at the bottom end, but opening out at the side into two short arms forming a broad horizontal Y. Rubber hose connects these arms to two discharge tubes, which terminate in rearward-pointing nozzles 3ft. on either side of the aircraft centre line, 2in. below the wing surface, and lft. in advance of the trailing edges of the wings. That position was chosen because; it is close to the outer edge of the slipstream, which serves to broadcast the droplets over a wide area. , - Preparation of Solution An -saturated solution of commercial hydrated cobalt sulphate was prepared in 44-gallon drums by weighing 1921 b. of the salt into 32 gallons of water heated to about 150 degrees F. by army petrol cookers of the blowlamp type. The volume of the resulting solution increased to about 40 gallons. > When cool the volume was somewhat less. but was topped up again to 40 gallons. The solution, which was prepared a day in advance, was warmed again before being pumped into the tank in the aircraft. It was thought that if the liquid was spread while warm there would be less danger of its crystallising out around the discharge jets to . cause blockage or a lowering of the rate of flow. In practice it was found that there was no tendency for that to occur. Measurement of Spread ' . As a working basis it was assumed that while topdressing was in progress

the average speed of the aircraft would be about 100 miles an hour. As the discharge rate had to be adjusted so that the aircraft could cover 60 acres as completely as possible with one load, it was necessary to determine the effective width of spread. It was decided that, where conditions permitted, the aircraft would topdress from altitudes as low as 150 ft., and preliminary spreading trials were therefore conducted at that altitude. For a first approximation trials were made using water, two observers on the ground defining the width of the resulting shower. Those tests were carried out first at Rongotai and later, when the discharge rate had been adjusted, at the improvised airfield at Waimiha before topdressing commenced. Final tests were made with cobalt sulphate solution' over the river valley flats of the farm (area C) during calm weather. Under those conditions a satisfactorily-even spread of about two chains could be accurately applied.

Adjustments to the rate of discharge of liquid from the tank were made by pinching up the ends of the discharge pipes. Preliminary tests were done with water on the ground, but as expected in flight the rate of discharge was raised appreciably. Finally, the discharge rate was regulated to deliver 15J gallons of water in about 130 seconds from the air. The rate of discharge of cobalt sulphate solution was subsequently checked while spreading was in progress and gave reasonably good agreement.

For assessing the width and evenness of spread of solution over the river valley flats rolls of toilet paper were employed, chemically treated so that when drops of cobalt sulphate solution came into contact with the paper an easily -visible blue colour was produced. The rolls were pegged out in lengths of up to 150 yards at right angles to the line of flight of the aircraft. Similar tests were made while topdressing was in progress over the easy rolling country (area A). Time did not permit of the laying of test paper while -topdressing the hilly country (areas D and E), where spread and drift of material had to be assessed by eye, so the' information obtained was less reliable than that available for the flat and easy rolling country.

Effect of Wind

Wind speed on the ground was measured by a small cup anemometer. Width of spread varied considerably with wind direction and velocity as well as : with.the nature of the terrain and the altitude of the aircraft. Observations made during topdressing may be summarised as follows: —

1. In calm weather a measurable

spread of about 44 yards was obtained from an altitude of 150 ft. Size of drops appeared to vary from moderate-sized raindrops near the middle of the spread to small rain-

drops showing less scattering toward

the edges. Little or no fine spray was discernible.

2. With the fairly-steady 15 miles an hour cross-wind which prevailed from the north while topdressing was in progress over the easy rolling country (area A), a discernible spread of up to 120 yards was obtained from an altitude of 150 ft. Some of the material appeared to be broken up into spray. The windward edge of the shower was considered to be' displaced about 50 yards downwind before reaching the ground.

3. With turbulent 15 miles an hour south-westerly winds over the hill country (areas D and E), it was necessary to topdress from an altitude rof about 200 ft. above the hilltops, which at times meant about 400 ft. above valley . floors. Though no accurate estimate was possible under those conditions, it was considered that with the aircraft flying cross-wind spread would be of the order of 200 yards. As before, a portion of the droplets was broken up into spray. As a rough approximation, it was estimated that in some cases a part of the material was displaced downwind for distances up to 300 yards before reaching the ground in the valleys. A complicating factor was that, while turbulent winds prevailed over the hilltops, in .the valleys winds varied from calm to moderate and variable. On one occasion, while topdressing area E, the hilltop wind rose to 20 miles an hour and operations were discontinued, as it was considered that conditions were too hazardous for flying and accuracy of placing might be reduced below a satisfactory level.

Spreading Organisation

Where possible spreading was .. conducted according to a prearranged plan. On the river valley flats of area C banners were placed at 44-yard intervals at right angles to the line of flight. As the aircraft made a run over each banner the banner was removed. A similar system was employed in topdressing the easy rolling country (area A), where conditions allowed straight runs of a mile to be made parallel to the boundary fence.

Having established that 44-yard intervals would give the ideal coverage, the greatly-increased width of spread in cross-winds was of no great consequence. Though each run resulted in a lighter coverage than required, that was offset by the application of further material from subsequent runs over a large proportion of the area already covered by previous runs. On the steeper country time did not'

permit the use of the banner system, and ground organisation was employed only in flagging boundary, corners where they were not clearly delineated by fences or by contrast between

pastured land and bush. Fires were lit on prominent ridges to indicate wind speed and direction to the pilot.

Radio communication was maintained throughout the experiment by personnel of the Army Signals Wing, Trentham, permitting discussions between the pilot at the airfield and the ground organisation at the site of spreading. Radio communication with Trentham was also arranged, enabling a daily weather forecast to be obtained by telephone from Wellington and transmitted from Trentham to Waimiha.

Flying Technique

With calm conditions the chemical tests indicated a very satisfactory evenness and accuracy of spread on flat land, but' with the winds which prevailed while spreading was in progress over the hill country (areas D and E) evenness and accuracy were reduced by turbulence and variable wind conditions in the valleys. To drop the load within a given area the aircraft was flown at least 300 yards inside boundaries toward which the wind was blowing.

Windy conditions necessitated considerable improvisation of flying technique according .to topography and orientation of area boundaries. Where conditions allowed long straight runs, normal procedures were followed, the pilot working. out a definite portion of the area by spreading at two-chain intervals as far as could be assessed by eye. Under other circumstances it was necessary to work along contours on the windward sides of ridges, leaving the valleys to leeward practically untouched. Several very deep valleys had to be left altogether to be topdressed later during early-morning calms. On a morning when conditions were sufficiently calm,

“filling in” work was done over the hill-country areas with the remaining portion of their cobalt requirement. That was accomplished by flying as low as possible inside boundaries, and by diving into valleys to drop further material where ,it . was considered little or none had reached from previous applications. By those means an effective distribution was thought to have been applied to the hilly areas.

Effectiveness of Operation

The effectiveness of the topdressing may be discussed under two headings:— ?• . - .

1. Is aerial topdressing with cobalt sulphate technically possible in that the required amount can be distributed over a given area in such a manner as to control bush sickness effectively?

2. Is aerial topdressing with cobalt sulphate economically feasible?

This experiment has shown that cobalt sulphate can be distributed over flat country with considerable evenness . and accuracy under calm conditions. With similar weather it is reasonable to suppose that a comparable evenness and accuracy could be realised over hill country. To topdress easy rolling country completely in one operation winds up to 15 miles an hour are allowable. With 15 miles an hour turbulent winds hill-country spreading can be accomplished, but small blocks of country with irregular outlines require “filling in” work under fairlycalm conditions. Winds in excess of 15 miles an hour are likely to give a less satisfactory distribution for single small-farm operations. However, if large topographical blocks were being dealt with, accurate placing would become of diminishing importance and it should therefore be possible to topdress in higher winds at greater altitudes.

Exact evenness of distribution is not essential, as the lower cobalt content of pasture topdressed at low rates is offset by the higher content of pasture topdressed at high rates, provided the grazing animal has free access over a reasonably-large part of the topdressed area. The' present work was satisfactorily carried out in that cobalt sulphate was applied from the air at a rate sufficient to control bush sickness.

The economic feasibility of aerial topdressing may be considered in relation to other methods available: —

1. Cobaltised superphosphate: The difficulty of application and distribution costs of cobaltised superphosphate are no greater than those of ordinary superphosphate. Clearly, then, aerial topdressing of cobalt sulphate alone would have no application where it is feasible to topdress with cobaltised superphosphate by agricultural machinery or by hand. The possibility of topdressing with cobaltised or ordin-

ary superphosphate by air poses a different set of problems to which the present work offers no direct solution. 2. Cobaltised licks: Licks are a less satisfactory alternative to topdressing in that they are uncertain in action, as some ,animals will not take them. Periodical labour charges are entailed in mixing licks and replenishing the lick boxes. 3. Topdressing with cobalt sulphate by hand: Few data are available for the cost of application by hand, as cobalt sulphate when applied as a topdressing is normally incorporated in superphosphate. ? In the present instance, it has been estimated by the owner that the cost of application of cobalt sulphate crystals to the farm by hand would be at (least Is. an acre, a total of £9O for 1800 acres; moreover, the difficulty of securing an even distribution would be considerable. Costs of aerial application have worked out at 7d. an acre, a total of £52 10s. Od. for 1800 acres. Assuming the cost of the

present work to be roughly representative of that of any similar enterprise, aerial topdressing would compare very favourably with hand topdressing. In a commercial undertaking the cost of aerial topdressing would be influenced by a variety of factors, including the type of aircraft available, the weather encountered, the amount of ground organisation necessary, and the distance of a suitable landing field from the site of topdressing. Of prime importance is the size of the farm to be topdressed or the number of adjoining farms which could be done by neighbourly arrangement during one series of operations.' It would be technically more simple, and therefore more economical, to topdress larger blocks of land than small. The writers are of the opinion that the experiment has shown that cobalt sulphate can be successfully and economically distributed from the air. The particular importance of the work is that it offers a satisfactory solution to the cobalt , top- .

dressing problems of hill-country farmers.

Acknowledgments The writers are indebted to Dr. I. J. Cunningham, Animal Research Station, Wallace ville, for advice and help in planning the experiment, Mr. J. Frizzell, aircraft engineer, Public Works Department, for help in the design and maintenance of equipment, Mr. E. G. Stainton, Fields Instructor, Taumarunui, for much of the preliminary organisation, Mr. E. A. Wright, Animal Research Station, Wallaceville, for assistance at the farm, Mr. L. Park, manager, Native Development Block Scheme, Waimiha, for making the airfield available and assisting in the ground organisation, and Mr. J. Allison, Waimiha, for assistance at the airfield. The writers also desire to acknowledge the assistance of the Vacuum Oil Company in providing a mechanically-operated transfer pump free, and the co-operation of Army Signals Wing, Trentham, in providing and maintaining wireless communication. The aircraft was piloted by A. M. Prichard. ’