New fertigation trial will examine its effects on nutrient losses

A new project to trial the use of fertigation – which could help reduce nitrogen leaching on farms – is now underway.

Pāmu (formerly Landcorp) is working with IrrigationNZ and Ballance Agri-Nutrients on the trial which has 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 is uncommon in New Zealand.

In September 2018, IrrigationNZ organised a study tour of Nebraska which visited farms and research institutions. IrrigationNZ Technical Manager Steve Breneger was one of the tour participants.

“In Nebraska, fertigation used 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,” says Steve.

“Fertigation allows for small amounts of fertiliser to be applied at a time, allowing more uptake of nutrients by crops. The farmers we spoke to talked about how it helped save on labour and reduce wear and tear on equipment as tractors don’t need to be used to apply fertiliser, and also that it worked out as a more cost effective way of applying fertiliser over the longer term,” he adds.

Pāmu started using fertigation in November last year at a Waimakariri dairy farm, and plans to expand the number of farms fertigation is used on to seven farms in Canterbury and four farms in Taupo.

Pāmu Farm Innovation Specialist Roo Hall joined part of the IrrigationNZ tour to Nebraska and was able to talk with fertigation specialists and farmers about the setup and use of fertigation.  He also attended a Fertigation Masterclass which IrrigationNZ held in 2018.

“The farmers I spoke with in Nebraska were concerned with the pressure on commodity prices. By using fertigation they were able to reduce their expenditure on fertiliser which was one of their biggest expenses. Some farmers who had adopted fertigation were using up to 30-50% less fertiliser than conventional bulk applied farmers and still getting similar yielding crops in all instances.”

“Here in New Zealand we wanted to trial fertigation to see if we could reduce our nitrogen losses while still maintaining our productivity on farm,” says Rob Ford – General Manager Innovation and Technology at Pāmu who is overseeing the trial in New Zealand.

Rob says that the process of installing fertigation equipment has been pretty straightforward, due to some of the key components being already available on overseas and local markets.

“If you mix the fertiliser on site and it isn’t mixed correctly 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 has installed a 30,000 litre tank on site and the fertiliser is delivered once a month.  A smaller 4,200 litre tank has been mounted onto a trailer and sources fertiliser from the larger tank. The trailer is rotated around the farm by tractor and connects to the base of pivot irrigators to supply nutrients. The trailer spends a day at each location so fertigation is carried out on a weekly cycle to each paddock in conjunction with irrigation scheduling.

Pāmu  expects to pay off the cost of the installation of their fertigation system after four years and from then onwards it expects to save money on its fertiliser costs.

One of the main differences between using fertigation and conventional nutrient application via ground spreading or aerial top dressing is that as it does not require any additional labour to apply the fertiliser it allows for small quantities of fertiliser to be applied at a time.

To date, on the first farm Pāmu has started using fertigation on they have reduced their overall fertiliser use by 20% over the summer.

As part of the trial, a Master’s student who is supervised by Lincoln University will be engaged to carry out research on how using fertigation has affected the nitrogen losses on Pāmu farms. Data will be collected over two irrigation seasons.

Nitrogen leaching losses haven’t been calculated yet – but they could be higher than 20% as research undertaken to date in other countries has indicated that crops are better able to use nitrogen when its applied in smaller quantities, resulting in less nitrogen leaching.

Rob says that the quality of the pasture and fodder beet crop which is receiving fertigation actually looks better visually than it did before, with tissue sampling that back these observations.

“Not having contractors spreading fertiliser over the summer has meant that there is less compaction to the soil, less diesel being used and less health and safety issue to monitor on the farm,” he adds.

The farm has been using fertigation since the November and will use it until the end of March but it will use ground spreading to apply fertiliser in the spring and autumn time. This will provide the option to compare nitrogen losses as part of the trial between the two methods of applying fertiliser.

The trial will also look at the costs and benefits of using fertigation, as well as the practicalities of using it on the trial farms.

IrrigationNZ also released a guide to the use of fertigation in New Zealand for its members in December. The guide can be accessed online at (search for ‘fertigation’).

“Fertigation is a precise science,” says Steve Breneger. “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. There are some pitfalls that can occur and the guide explains how these can avoided.”

A Fertigation Masterclass was delivered by IrrigationNZ in 2018.  IrrigationNZ has plans to deliver the class regularly in the future in order to upskill farmers, irrigation designers and irrigation service professionals on the correct use of fertigation.

IrrigationNZ will keep irrigators up to date on the results of the field trial as they are released in the future.