Crops grown near airport runways are providing multiple benefits: cooling the air, helping aircraft take off, and providing extra income.

Key points: A business case is being put forward to decide if SA Water and Adelaide Airport should expand the lucerne trial

A business case is being put forward to decide if SA Water and Adelaide Airport should expand the lucerne trial The trial has found the crops lower temperatures, helping aircraft take off

The trial has found the crops lower temperatures, helping aircraft take off Thousands of tonnes of lucerne hay could be cut and sold each year

A world-first, four-hectare trial site of lucerne hay is being grown near the runway at Adelaide Airport in conjunction with SA Water.

The crop has helped lower temperatures in the vicinity by more than 3 degrees Celsius, which has the added benefit of helping planes take off.

Environmental opportunities manager at SA Water, Greg Ingleton, said they came up with the idea to try to green-up the space around the runway, but the initial idea revolved around the terminal.

"When we first started the trial with irrigation it was really aimed at cooling the air so that it might be cooler around the terminal and the air conditioners would use less energy," he said.

But after a conversation with a pilot friend, Mr Ingleton said the benefits to aircraft performance would be quite significant.

"The biggest issue on hot days is that the planes actually can't take off with their full payload because there is a certain temperature they need," he said.

"Once the surface temperature, or air temperature around the runway, gets above that they actually have to take things like cargo off the plane.

"And so finding out about that, I thought we could see what type of temperature reduction we could get."

Andrew Neely is a professor in aerospace and engineering at UNSW Canberra, as well as the vice-president of the International Society of Airbreathing Engines.

He said airbreathing engines, or jet engines, needed thrust to take off and if the temperature was too hot or the airport was too high above sea level it could play a big part in the plane not being able to take off.

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"Engines produce their best thrust at lower temperatures and lower altitudes, so if the weather is particularly hot and the air is thinner then the engines will not produce as much thrust, which means the aircraft cannot accelerate as quickly as possible for take off," Prof. Neely said.

He said this was where airline companies needed to make decisions about what they could and could not carry.

"This can definitely impede on the ability to carry as much into the air and their ability to operate at maximum take-off weight, which means the maximum number of passengers and fuel," Prof. Neely said.

"It can become more marginal for long-haul aircraft where they need a very heavy fuel load. You have a large aircraft with a lot of people and a lot of luggage and sometimes freight as well, because they want to fill up the aircraft to make as much money from the trip as possible.

"But when you have particularly high temperatures, you have to leave some of that off and then that starts to eat into your margin."

The lucerne crop is about 600 metres from the Adelaide Airport runway, and provides a cooling effect. ( Supplied: SA Water )

Lucerne offers most benefits

The SA Water team trialled a number of grasses, such as tall fescue, couch and kikuyu, but lucerne was found to have the most benefits.

That was where the idea for a crop that could be turned into an added profit came about.

"During the set-up of it I was talking to the maintenance guy at the airport," Mr Ingleton said.

"He wasn't too supportive of it because he would have to mow the grass more if we are growing something — and irrigating it.

"My comeback to that was 'Well, why don't we grow something that when we cut it you guys can actually make some money out of it?' … and hence the reason for choosing lucerne."

While the trial has shown lucerne dropped temperatures around the runway, senior research agronomist, Jason Brand, said simply by covering the dark soil with any plant could cool the area.

"Soils are usually a darker colour so when the sunlight hits it during the day it heats up," he explained.

"So if you have plant material or even stubble cover over it, it reduces the ability for the soil to heat up during the day."

He said this was being seen a lot more with cities growing trees and grasses to cool areas down.

"We have seen that in the major capital cities where we see suburbs with a high level of trees generally have cooler temperatures simply because you're not getting as much of the sunlight being absorbed through roadways or dark-coloured buildings," Mr Brand said.

"So any sort of plant would probably do a pretty similar thing as long as it is green and growing, it will certainly help reduce temperatures … but lucerne does have the benefit of being able to be cut for hay."

Added benefit of keeping birds away

Apart from being able to be cut for hay and sold as feed, the lucerne also appears to deter birds — something that can be a huge headache for airports.

Mr Ingleton said lucerne was looking like it would be a good deterrent.

"Just standing back and watching mainly flocking birds, they like to dig in the soil and get seeds and grubs out of the soil," he said.

"But if you have a nice thick crop of lucerne over the top of the soil [the birds] can't actually get to the soil and the movement of the crop in the wind also spooks them."

Adelaide Airport's senior environmental advisor, Leigh Gapp, agreed that a key component of the trial would be to minimise any wildlife hazard.

"The initial results [of bird trials] seem positive, but we need to increase the area of lucerne sown and continue monitoring bird activity at the site to confirm the preliminary results," Mr Gapp said.

"We have not seen an increase in the numbers of high-risk species such as galahs, corellas and pigeons at the existing lucerne plots.

"The fact that it can be cut before flowering, insects can be managed, and the growing height is in line with the internationally accepted 'long grass policy', makes it a good candidate for further research."

Pollution concerns

The lucerne currently being grown at the airport has not yet been harvested for hay and is yet to be tested for any presence of airport pollution, such as fuel fumes.

The lucerne crop at Adelaide Airport has been cut regularly during the trial. ( Supplied: SA Water )

But Mr Ingleton said the distance from the runway, about 600 metres, should mean that it would not be an issue.

"When you are down there the crop itself is quite a way away from the runway itself, plus the apron and any plane movement areas," he said.

"I haven't smelt any fumes when I have been down there at the lucerne crop. It is south of the runway so there is a bit of a sea breeze there that should blow any fumes away from the crop.

"There would be more potential pollution coming from any surrounding roads, but we will be doing some tissue testing to confirm that."

Plans to expand

The plans now are to expand the trial to use a permanent centre pivot irrigation system to water the crop, which has the potential to grow up to 200 hectares of lucerne and 50 to 100ha of irrigated turf near the main runway.

Both SA Water and Adelaide Airport were discussing how to progress to the next stage, but were also keen to start looking at some of the other benefits.

SA Water's Greg Ingleton says growing crops near regional airports would also see benefits. ( Supplied: SA Water )

"We could look at how to get that soil carbon benefit, which might be another income or benefit from capturing that carbon," Mr Ingleton explained.

"We are also wondering if that could be a selling point that we can take to the airlines and if there is some sort of investment where they get a benefit from it with carbon credits and the airport would get the benefit from the sale of the lucerne.

"It is one of those projects that everyone would benefit from because SA Water will also benefit from the sale of recycled water … and the airlines can save money on hot days."

Mr Ingleton said it was also something that regional airports could look into.

"It is well known that some regional airports actually operate at a loss and we were thinking if there was a good water source that was available, like groundwater or another alternative source, that it would be a good crop to be growing," he said.

"The propeller planes that you might see at a regional airport don't get as big a benefit as a jet engine when it comes to the temperatures, but it is still a really good use of the land that would otherwise just sit there."

Mr Gapp said they would also continue to investigate the extent of the benefits to the airport.

"We will look at the cooling that can be achieved with irrigation and the potential benefits aircraft and airport operations, including aircraft fuel use reductions and improved building heating, ventilation and air conditioning operations," he said.

"Additionally as part of our strategic approach to understanding and mitigating impacts of climate change, Adelaide Airport Limited is trialling lighter coloured 'cool' pavement applications on our apron and runway edges."

