Variable rate fertiliser technology saves cash and lowers nutrient footprint

Variable rate fertiliser technology allows fixed wing plans to apply fertiliser at a rate to better match the capability ...
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Variable rate fertiliser technology allows fixed wing plans to apply fertiliser at a rate to better match the capability of the land.

Technology that opens and closes a hopper in a top dressing plane to fertilise only parts of farm that need it could put an end to blanket fertilising.

The technology would help farmers be smarter with their fertiliser use, save them money and improve their environmental footprint, Ravensdown development manager Mike White told farmers at Limestone Downs Station.

The sheep, beef and dairy farm is one of about 40 farms in New Zealand that have used the technology.

The first step in using the technology is to divide the farmland into blocks called land management units. Each of these units is individually assessed using soil tests.

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This gave the farmer a understanding of their farm's variability and allowed them to apply the fertiliser and lime accordingly, White said.

"That's exactly what we have done with Limestone Downs."

A year ago aerial applications of superphosphate at 150 kilograms and 250kg per hectare ere put on 1833 effective hectares across 2014ha of the farm.

"That's 181ha that we haven't ordered fertiliser for, we haven't carted it on a truck, we haven't put it into a bin and we haven't put it into a plane. The broadcast costs of that are about $11,000."

The fertiliser was also applied without the pilot touching a single lever in the plane, White said.

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Instead, a GPS is fitted with a prescription map of Limestone Downs is attached to the plane and tells the plane its location as it flys over.

A computer is placed in between the GPS and the fertiliser hopper and opens and closes the hopper as it flys over the application area. The hopper can also adjust its rate as the plane slows or speeds up. 

Using the technology occasionally meant extra flying time if the hopper ran out of fertiliser during the application.

"Based on the 40 jobs we have done, the additional cost is less than 5 per cent of the total cost if we had been flying conventionally. Yes there is an increased cost, but it is quite small in the scheme of things, " he said.

In the future, farmers will be using remote sensing to determine their soil fertility, which will enable fertiliser to be applied much more precisely.

The technology was ideal for Limestone Downs Station where there were multiple soil types that required lots of soil testing. Work around the technology was part of a Primary Growth Partnership project Ravensdown was involved with.

Limestone Downs was one of eight research farms where the study was taking place. The long term study was calibrating a hyperspectral soil sensor that was capable of measuring soil fertility from 20,000 soil samples, he said.

White said they had set up 400 sample sites at Limestone Downs.

An 80kg sensor is attached to a plane and is flown over the farm at 2000 feet, taking a 200 metre wide measurement of the farm as it flies over. That information is recorded to one square metre of accuracy.

"For every square metre of Limestone Downs, it's giving us a signal on that pasture that it's reading. For every hectare, we are getting 10,000 measurements. That's a lot of soil tests."

Across the whole farm, that equated to 20 million measurements, he said.

Using the technology, White was able to show the pasture's nitrogen, potassium and phosphorous concentration.

"How we see this being used is to produce a soil fertility map across the property. It would be something you would do maybe every four to five years."

 The project was in year four of seven and the big challenge was relating soil pasture nutrients to the underlying soil fertility on the project farms.

"I would say this is just the starting point and for a minimum to establish these relationships, it will take us about 20,000 soil and plant tissue samples. We have already collected around 13,000 so we're well underway."

 - Stuff

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