Scientists warn that populations here and around the world are growing so fast that it will curtail countries' ability to feed their own people.
It may sound improbable, but they warn that urban sprawl could limit even New Zealand's ability to be self-sufficient in vegetables, especially if Auckland keeps expanding at a seemingly inexorable rate.
In Pukekohe's case, the area owes its superior fertility to an eruption in the central plateau 250,000 years ago, which rained down tephra ash material that just happened to have the growing properties Pukekohe has become known for, says Auckland Council land and soil scientist Fiona Curran-Cournane.
"It is well-structured soil. It can withstand continuous cultivation and that's down to the versatility of the land, the soil type, climate, and the fact that it's flat," she says.
As luck would have it, Pukekohe is also in a special position geographically: it's relatively free of frost but doesn't have the same risk of pest incursions that can hit crops in the warmer climates to the north. "All those factors make it really unique and conducive to outdoor vegetable production," says Curran-Cournane.
This versatile land represents a small part of New Zealand's total area, yet it is responsible for a disproportionately large part of New Zealand's outdoor vegetable production.
Pukekohe's claim to fame is that the land can be cultivated continuously, making it good for two or three crops a year.
Experts rate land on a scale from one to eight. The "elite" soils are class one. At the other end of the scale is class eight - sand dune material.
The class one land around Auckland is exclusive to South Auckland and Pukekohe. Only classes one, two and three are suitable for vegetable production.
The further down the soil quality scale, the greater the need for fertiliser. More fertiliser means greater nitrate runoff, which then raises water quality issues, so setting up shop in lesser soil types carries greater economic and environmental costs.
Contrary to popular belief, New Zealand does not have an abundance of rich soils. Most of it is class six - suitable for pasture or forestry, but not much else.
Curran-Cournane, in a research paper presented at a soil science conference last year, said the development of Auckland's elite land had been set in train under previous land-use planning regimes and is set to continue under the recently adopted Auckland Unitary Plan.
She says 14 per cent of Auckland's class one land has been or will be encroached upon by various forms of development by 2040, as well as 31 per cent of its class two and 18 per cent of class three land. Curran-Cournane says the real "red flag" for her is what looks likely to happen to class two land, as in production terms, there is very little difference between classes one and two.
"As a region, for elite and prime land, we are doing quite well but also we have seen a lot of tradeoffs as well because that land is good for houses as well."
Horticulture New Zealand chief executive Mike Chapman wants the 5.5 per cent of New Zealand's landmass that is used for fruit and vegetable production to be preserved.
He says that since 2001, we've lost about 10,000ha of growing land - 6000ha for vegetables and 4000ha for fruit. That's an area just under the size of Hamilton.
"What it's showing is that we are losing valuable land to houses and lifestyle blocks," Chapman says.
"The problem with that is that it is very difficult to keep growing the same amount of vegetables to feed New Zealand at certain times of the year.
"At this time of year - spring - it is a difficult time for vegetables, mostly because it's pretty cold down south.
"This year is particularly difficult because it has been so wet everywhere, but in a normal year, Pukekohe is a key growing area," he says.
New Zealand horticulture is big business, and growing fast.
With an industry value of $5.6 billion (excluding wine), New Zealand exports 60 per cent of what it grows - $3.4b in value, to 124 countries.
Those exports increased by 40 per cent from June 2014 to 2016. The 5500 commercial fruit and vegetable growers employ about 60,000 people and the demand for workers across the skill spectrum is outstripping supply, according to a KPMG report.
Most of the vegetables grown in New Zealand are consumed here. The exception is the onion crop, 90 per cent of which is exported.
While the majority of vegetables were grown near main centres 40-50 years ago, there is now more of a reliance on large food production hubs - Pukekohe, the Horowhenua and Canterbury.
KPMG said of the 5.5 per cent of land appropriate for vegetable production in New Zealand, roughly one tenth has been subdivided for lifestyle blocks over the past 15 years.
In Pukekohe - where most of Auckland's class one land is located - the plan is to take the current housing stock from 20,000 to 50,000.
"We think that it's very important that New Zealand grows and supplies its own vegetables, and obviously there is an export market there too," Chapman says. "But our prime concern is that we need the land to grow vegetables to feed New Zealand.
"All we are asking for is the 5 per cent of land around New Zealand that is good for horticulture to be protected as much as it can be.
"We would be very keen to see the houses go somewhere else to protect domestic production."
Understandably, there is competition from developers. What is good for growing - flat land - is good for housing development too.
Chapman says it's a similar issue in other parts of the country.
"In Christchurch, as the city pushes out from the earthquake, a lot of small growing operations, on all the city's boundaries, a lot of vegetable operations there are slowly turning into houses as the city expands."
Chapman says Christchurch's urban sprawl has seen growers shift to south Canterbury. Further south, in Central Otago, the threat of lifestyle blocks has taken out valuable fruit and vegetable land, he says.
Some Pukekohe growers are going south to the Waikato but there are issues there too, as the Waikato Regional Council embarks on its Healthy Rivers campaign.
But Auckland deputy mayor and former Franklin local board member Bill Cashmore believes Pukekohe's class one land is adequately protected.
The development taking place is mostly the result of "legacy" zoning decisions made by the former Franklin District Council (FDC), he says.
The last subdivision there was Belmont, he says, which was approved in 2010. Since then, the Franklin local board had "hard edged" all the good soils, protecting them.
"There has been some legacy subdivision allowed around Belmont and around the back of Patumahoe," he says. "Again, it was stuff that was FDC approved but that is coming to an end. Once those developments are finished, that will be it," he says.
"There is no more encroachment. People can apply for a private plan change but it is against all the regional policy statements to lose that productive rural land to residential."
Auckland's population is projected to reach 2.4 million by 2047, requiring 400,000 new dwellings.
The Unitary Plan has identified 423,000 potential dwelling sites - 123,000 of them in rural areas.
Cashmore says the challenge now is finding the infrastructure for that growth. "What we have got to do now is focus on those brownfields developments, which means some intensification of what is in the urban area now," he says.
NZ Property Council chief executive Connal Townsend says issues around the protection of Auckland's productive land have been largely resolved. "We still have concerns about the overall planning system - the Local Government Act and the Resource Management Act - and we think there's a need for a fresh look, but in terms of Auckland, for the moment, it's kind of resolved."
Auckland Council land system scientist Nancy Golubiewski says it's not just a matter of urban sprawl.
There's also "rural fragmentation", where the traditional land uses are up against the expansion of lifestyle blocks.
She says Horticulture NZ's food security concerns are not that far-fetched.
"Will other countries, as New Zealand comes under pressure, be so willing to export their food resources to other countries?" asks Golubiewski.
"The issue is that as very good farmland gets transformed to non-productive use, that production has to push out to elsewhere, so there is a ripple effect," she says.
"The question is: where is elsewhere?".
"The question is: where is elsewhere?"
Urban sprawl never far away
For third generation Pukekohe market gardener Bharat Jivan, the threat of urban sprawl is never far away.
Jivan, who crops 200ha of land around the fringes of Pukekohe, only has to look over the fence to see the advance of bricks and mortar.
He grows mostly potatoes and onions - the latter destined for northern hemisphere export markets.
Much of the land he crops has been zoned "future urban" and he's just lost 3ha to developers when his landlord sold up.
Jivan thinks the land needs more than just local authority zoning to protect it.
"It can be in the plan, but if there is a change of council and the plan gets reviewed, it's all up in the air again," he says.
"So it's back to square one and we have to start lobbying the councillors and telling our story again."
Jivan's family has been growing produce in Pukekohe since the 1960s. In the area, there is land that has been zoned "future urban" that is now being cropped.
"I imagine the rates will be increasing because of that zoning, and that puts a lot of pressure on the existing land users to sell up and develop that ground, because of the rates that they are paying," he says. Jivan says there's no doubt the area's soils are special.
"It's very fertile and free draining, so that when you have periods like we have just had - the soils around here can withstand the rain a lot better.
"We have not really encountered any crop losses through the wet season," he says.
The area has plenty of "early ground" that lends itself to early planting. That means potatoes planted in May can be harvested in October and November - well before anywhere else.
He bears no ill-will towards growers who sell land to developers. For many, he says, that simply reflects the lack of a succession plan.
Jivan feels former Housing Minister Nick Smith's Special Housing Area policy has not done locals any favours.
The policy identified 154 areas around Auckland to speed up zoning for the development of 66,000 houses.
Likewise, incoming minister Phil Twyford's comments that the government planned to remove the urban growth boundary and free up density control, to solve the city's housing shortage, have not gone down well.
"The land values have really been pushing up to the point where it becomes uneconomic to crop. That's the other issue - because the rates go up," Jivan says.
He wants the government to "put a peg in the ground" and preserve high quality land for food production.
"In the short to medium term, there needs to be a a national policy in place to protect this soil," Jivan says. "Because we can't compete with land developers."
