SPRAY IRRIGATION COSTS

Press, Volume CXII, Issue 32862, 10 March 1972, Page 12

SPRAY IRRIGATION COSTS

The accompanying item on spray irrigation systems and their costs has been written by D. M. Cross, farm advisory officer (agricub tural engineering) of the Department of Agriculture, Blenheim.

Moving irrigation pipes does not necessarily involve back-breaking toil shifting pipes by hand three or four times a day. Gone are the days of struggling out of bed in the early hours of the morning to set up an irrigation system for another few hours watering.

There are many new machines coming on the market, which make possible a drastic reduction in labour input. Although this equipment costs more to buy than conventional systems, the lower labour requirement makes it economically attractive. The basic, trusty sprinkler irrigation system of the past has been the portable, hand-move system using aluminium pipes with sprinklers set at regular intervals. Operators realised that if skids or wheels were attached to the sprayline, the whole line could be pulled by a vehicle. So evolved the tow-a-line system. With this system, wheels in the form of a “dollie” or “bogie” are fitted into a conventional sprayline. Special joiners are also attached so that the pipe cannot pull apart. These wheels are totally enclosed, fully galvanised, and 4in wide for maximum floatation. The 3in, 4in or sin aluminium pipe can be above or below the harness connecting the two wheels. This equipment can be moved by two methods. The simplest (and cheapest) form is the end-tow method, where the wheels track in line, one behind the other. The pipe is moved by breaking the line in the middle, and moving in two elongated “S” movements to the next set. This involves a certain amount of manoeuvring. The other method has automatically pivoting dollies. This allows the 20chain sprayline to be shifted in two diagonal moves herringbone fashion, from one sprayline setting to the next. This operation is quite simple. A tractor is connected to one end. The dollies pivot 45 degrees to shift the line 30ft. The tractor is then connected to the other end, the wheels turn through 90 degrees, so that the line moves 30ft in the opposite direction to the

z first half move. To simplify i coupling the sprayline after - each move, the first section i of sprayline telescopes to i provide an adjustable > length. Self-draining sprinkler ■ couplings aid the rapid . draining of spraylines. They are operated by a positive . seal that drains the line imi mediately the pressure is , released. ; The next step in automai tion, is to move the whole 20 chain sprayline in one i motion to the next setting. 1 To do this, large aluminium ■ wheels 46in, 58in or 70in in 1 diameter are connected at 1 regular intervals to a heavier gauge aluminium sprayline. The power source is a five horsepower petrol engine, mounted on a four-

wheeled carriage. There is a 1000 to 1 reduction between motor and wheels for easy control. The aluminium pipeline forms a continuous “axle” with sprinklers mounted at regular intervals. This type of sprayline can negotiate many row crops, even when the crops are planted in mounds, and the equipment is running across the mounds. With some makes line moving can be by means of a laddered, man-operated wheel, instead of a petrol motor. Most systems have some special device which controls the vertical placing of sprinklers. The largest type of irrigator at present available is the self-propelled big gun. This works on the cable/ hose concept Water is supplied from a buried main supply line, running perpendicularly mid-way across the wetted lane. A large sprinkler is mounted on a

small trailer unit, and is connected by a reinforced rubberised nylon hose to a hydrant in the mains supply line. A water-operated winch pulls the trailer along a wire rope that is attached to a solid Object on the far side of the run. When it reaches the end, it automatically switches off. Shifting time for this machine is about 30 minutes. However, the manufacturers recommend the use of a reel incorporating a p.t.o. powered compressor to purge the hose of water, for easier handling. The speed of these machines during operation is constant, although it can be varied between settings. Application rates vary between 23 and 37 points per hour, and in one setting up to nine acres can be irrigated. Operating costs for these machines are higher, as they require a working pressure of 70 to 951 b per square inch at the nozzle. It is all very well to look at these machines, but the important question is—“how much do they cost?” We must compare one with another. Each irrigation scheme has a series of fixed costs, which can be set down as follows: Digging and developing the well, power board and

electrician’s charges, pump, electric motor and starter motor and sundry installation charges: $2500. Mainline, assuming 6in pvc or fibrolite main all the way. Includes costs of hydrants at 300 ft intervals; 4000 ft at $1.25/foot: $5OOO. Total "fixed” cost: $7500. An Ordinary hand-move system, using light-weight aluminium pipes requiring 45 minutes to shift 20 chains. This will cover 1.5 acres per setting and costs $l5OO. A tow-a-line system 20 chains long, takes about 30 minutes to shift. It also covers 1.5 acres per shift

and costs about $2500 per 20 chains. The self-propelled lateral system also covers 1.5 acres per shift, but can easily be shifted three or four times a day, during crunch periods, as shifting only takes 15 minutes. These systems cost about $5500. This includes the four-wheel carriage with electric motor. The big self-propelled gun can cover up to nine acres per set, and requires 30 minutes to shift. However, extra mainline is required to cover a similar area, and also the p.t.0.-operated reel is extra.

Costs include: sprinkler, trailer, purger, hose and reel, $7000; extra mainline 5000 ft of 6in pipe at $l.BO per foot, $7000; total $14,000 (not so many hydrants needed). Each farmer has to decide for himself how much he can afford to pay. Naturally, as the machines become larger they cost more, but they will cover a greater area. In Marlborough, where large areas of irrigated lucerne will be required for increased meal production, “automatic” irrigation must play an important part