They also found 403.9 grams of methamphetamine, with a street value of about $144,000, and two firearms with ammunition.
At the time police believed they had cracked a major methamphetamine ring in Hawke's Bay and made a significant dent in the drug's supply, not just the region but to other parts of the country.
Irwin and Prasad denied the offending but were found guilty by jury almost three and a half years later after a seven-day trial held in the Napier District Court last month.
Irwin, 56, was found guilty of four charges each of possessing methamphetamine for supply and supplying the drug, as well as two charges of unlawfully possessing a pistol.
Prasad, 40, was found guilty of one charge of supplying methamphetamine.
At sentencing the court heard both Prasad and Irwin were patched Mongrel Mob members but Irwin was no longer an active member.
Judge Bridget Mackintosh said Prasad had been a "prolific" methamphetamine dealer and sourced the drug from Irwin.
Text message data was a key component in the case against the 40-year-old, with almost 300 drug transactions identified in messages he sent to people throughout the region.
He regularly travelled, sometimes late at night, and would often visit Irwin's farm; clocking up 30 trips in the space of seven months.
Irwin, described as a loner whose main friend appeared to be Prasad, had lived at his Te Haroto farm for 26 years and used methamphetamine on a daily basis.
In 2006 he was sentenced to three years' imprisonment on one charge of possessing methamphetamine for supply and one charge of possessing a pipe.
Judge Mackintosh said he lived with his son, partner and her children on the farm and noted she had received a heartfelt letter from his partner detailing Irwin's qualities and the support he had given her family.
However, there was "nothing to be said" about mitigating factors for Irwin's case, she said, and she sentenced him 13.5 years' imprisonment with a minimum non-parole period of six years and nine months.
A large question remained as to why Prasad, the father of a young teenager, had resorted to dealing methamphetamine, the Judge said.
The court heard he had offended for financial reasons but Judge Mackintosh said it was perhaps his association with the Mongrel Mob that had led him down a "slippery slope" of offending.
She sentenced him to five years' imprisonment with no minimum non-parole period.
A new study by Massey University suggests Hawke's Bay has the second highest rate of methamphetamine use in the country.
The study found Hawke's Bay was one of the regions in the North Island with the worst rates of drug dependency, ranking second for the use of methamphetamine and fifth for cannabis use.
The highest rate of methamphetamine use was in Waikato, with 43 per cent of those who used in the previous six months, closely followed by Gisborne/Hawke's Bay at 42 per cent.
In September last year Hawke's Bay police arrested 13 people, a number of whom were Mongrel Mob affiliates, for high-level drug offending after a six-month investigation into an organised crime unit.
Three kilograms of methamphetamine holding a street value of $2.5 million were seized, along with $343,000 in cash, 2200 LSD tabs, eight firearms, six upmarket vehicles and a brand new Harley Davidson motorcycle.
The maximum penalty for supplying methamphetamine is life imprisonment.
