The new laws allow for some exemptions for pest control.
Shaun Moloney, who culls pests including goats and wallabies across the South Island, said there was "definitely a place" for semi-automatic weapons with larger magazines for jobs like his.
"If you are having a very tightly controlled access to that style ... but it's still available, that is welcomed by several of my associates and myself," he said.
Hunting - with the kinds of weapons excluded from the ban - was an important part of life for his family, Moloney said.
"My daughter would go out and shoot rabbits, with a semi-auto, with me, and then we'd skin and gut it, she'd cook and eat it and then go to ballet," he said.
New Zealand's main farm lobby group quickly came out in support of the new laws.
"This will not be popular among some of our members but...we believe this is the only practicable solution," Federated Farmers Rural Security spokesman Miles Anderson said in a statement. "Christchurch, Friday March 15 has changed everything."
The main opposition National Party, which draws strong support in rural New Zealand, also backed the plans.
Under the changes, all military style semi-automatics (MSSA) and assault rifles will be banned, along with parts used to convert weapons into MSSAs and all high-capacity magazines.
The changes exclude two general classes of firearms which are commonly used for hunting, pest control, stock management on farms, and duck shooting: small bore rifles with magazines of no more than 10 rounds, and pump action shotguns holding no more than five rounds.
Bruce Plant, a rifle range club secretary in Oamaru, south of Christchurch, said there was little need for military-style weapons in New Zealand.
“If you are out hunting and can’t hit an animal with one shot you are certainly not going to hit it with 20 shots."
Experts say the changes don't go as far as Australia which toughened gun laws 12 days after the shooting of 35 people at Port Arthur in Tasmania in 1996. There all semi-automatic rifles and semi-automatic and pump-action shotguns are banned. There is also a restrictive system of licensing and ownership controls.
HIGH GUN OWNERSHIP
New Zealand has a lot of guns. With a population of just under 5 million, there are an estimated 1.5 million firearms.
In 2017, it had the 17th highest rate of civilian firearm ownership in the world, with 26.3 guns per 100 residents, according to the Small Arms Survey. The United States tops the list with 120.5 guns per 100 residents.
The last real change to New Zealand's Arms Act was made in 1992, following a shooting where 13 people were killed by a gunman with a semi-automatic weapon in Aramoana, a small South Island coastal settlement.
A special E-category license, which requires tough checks, was added to cover MSSAs.
Advocates say New Zealand's high gun ownership rates and low rates of gun violence are evidence of a system that works. Restrictions are certainly tighter than in the United States.
However, individual weapons are not registered, meaning police have little oversight over how many guns people hold.
Ardern said a further tranche of reforms will cover the firearm registry and licensing.
John Hart, a farm owner and former Green Party candidate, surrendered his semi-automatic rifle to police after the shooting, one of 37 weapons police said had been voluntarily returned ahead of the new laws.
"The time is right. I have spoken to many farmers who feel the same way. They have not given theirs (guns) back but they support the idea - although they won't do it until they have to."
Noel Womersley, who slaughters cattle for small farmers around Christchurch, said he was happy to sell his AR-15 rifle into a government buyback expected to cost up to NZ$200 million ($138 million)
"I'm using guns every day. I use them on the weekends, in my spare time, and I use them at work every day. But I don't need a semi-automatic military firearm."