State-owned farmer Pāmu was working with IrrigationNZ and Ballance Agri-Nutrients on the trial which had received funding from the Sustainable Farming Fund.
Fertigation is the application of small quantities of fertiliser through an irrigation system. Fertigation is used overseas but was uncommon in New Zealand.
In September 2018, IrrigationNZ organised a study tour of Nebraska, United States, which visited farms and research institutions. IrrigationNZ technical manager Steve Breneger was one of the tour participants.
"In Nebraska, fertigation use is encouraged by university academics and natural resource district officials who manage water as a tool to reduce nutrient leaching. The state had problems with high nitrate levels in groundwater, but nitrate levels are now reducing in many areas," Breneger said.
"Fertigation allows for small amounts of fertiliser to be applied at a time, allowing more uptake of nutrients by crops."
Fertigation helped save on labour and reduced wear and tear on equipment as tractors did not need to be used to apply fertiliser, he said.
It was also a more cost-effective way of applying fertiliser over the longer term, he said.
Pāmu started using fertigation in last November at a Waimakariri dairy farm and planned to expand its use to seven farms in Canterbury and four farms in Taupo.
Pāmu innovation specialist Roo Hall talked with fertigation specialists and farmers in Nabraska about the setup and use of fertigation.
They were concerned with the pressure on commodity prices," he said.
Fertigation allowed them to reduce the use of fertiliser which was one of their biggest expenses. Some farmers who had adopted fertigation were using up to 30 to 50 per cent less fertiliser than conventional bulk applied farmers and still getting similar yielding crops, Hall said.
Pāmu innovation and technology general manager Rob Ford said the corporate farmer wanted to trial fertigation to see if it could reduce nitrogen losses while still maintaining farm productivity.
Ford said the process of installing fertigation equipment had been pretty straightforward, due to some of the key components being already available on overseas and local markets.
Liquid urea fertiliser was used because it did not require mixing on the farm, he said.
"If you mix the fertiliser on site and it is mixed incorrectly it can be quite problematic. So we decided to keep it simple and use a liquid urea fertiliser from Ballance which doesn't require mixing on the farm."
The farm had installed a 30,000-litre tank on site, and the fertiliser was delivered once a month. The fertiliser was spread using pivot irrigators. A smaller 4200-litre tank was mounted to a trailer and sourced fertiliser from the larger tank. The trailer was rotated around the farm by tractor and connected to the base of pivot irrigators to supply nutrients. The trailer spent a day at each location so fertigation was carried out on a weekly cycle to each paddock in conjunction with irrigation scheduling.
Pāmu expects to recover the cost of the installation of its fertigation system after four years
Nitrogen leaching losses have yet to be calculated – but they could be lower than 20 per cent. Research undertaken in other countries had indicated that crops were better able to use nitrogen when applied in smaller quantities, resulting in less nitrogen leaching.
Berger said fertigation was a precise science.
"The correct type of fertiliser must be used, the irrigation system must be capable of delivering fertiliser and compatible with the type of fertiliser, and the mixing technique must also be correct. Some pitfalls can occur," he said.