Wednesday, July 6, 2022

Tested techniques to spread fertiliser efficiency

High fertiliser prices provide an opportunity to carefully consider soil fertility, nutrient needs and the calibration of spreaders, Ballance science strategy manager Warwick Catto says.

He told dairy farmers at the Northland Agricultural Research Farm, Dargaville, to take a really hard look at soil test variability across the farm, which could surprise in its extent.

“Even on relatively flat Waikato farms we have seen Olsen Phosphorus levels from 10 to 100.

“I have seen a particularly low potassium soil test on just one block of a Mid Canterbury arable farm, and that paid for 10 years of soil testing on that farm, from the economic benefit of getting that sorted.”

Catto said identifying the variability within the farm with comprehensive soil testing was key to making worthwhile savings on spreading.

“Most farms will have blocks with optimal or over-optimal legacy fertilities which can be exploited.”

Variability applied to all nutrients, phosphorus, potassium, sulphur and nitrogen, and to pH, he said.

Catto advised farmers to categorise their farm blocks into As, Bs and Cs, being best, medium and low potential, for the prioritising of fertiliser expenditure.

The highs would receive all the fertiliser they needed, the mediums maintenance fertiliser only, and the lows nothing.

“High-performing or valuable blocks, say with younger pastures, should get what they need to protect your investment.

“Low-performing blocks get nothing because the potential responses are of no significance to the farm performance as a whole.”

A main aim of fertilising pastures was to grow more clover content and therefore gain the cheapest source of nitrogen.

Areas of the farm with very low clover content could be left out of fertiliser spreading because the loss of dry matter would be trivial.

Catto also advised asking the timing question whether fertiliser applications could wait a season, to delay the cash outflow, although that required taking a position of the way prices will move in future.

“Where you already have high soil fertility, deferring applications doesn’t make a big difference.”

Aerial spreading should be concerned with slope and aspect of hill country and their differing pasture responses as well as soil test variability, he said.

Nitrogen fertility levels are the primary determination for dairy farms with already high soil nutrients and early spring applications are crucial to set up the rest of the season.

The second consideration should be spelling interval after N applications following behind cow grazing.

Plants take up nitrogen and slowly convert that into dry matter so to minimise animal urine N levels the grazing rotation should be 20 days or more.

Typically 10% of applied nitrogen disappears as ammonia, so the use of volatilisation inhibitors can cut that loss in half, thereby adding 5% more nitrogen response.

Finally, Catto emphasised the requirement for spreader calibration to even out fertiliser distribution across the ground.

While a Spreadmark accredited operator may cost more, they provide value for money by putting the right product in the right place at the right rate.

Mild temperatures in previous drought regions like Waikato have recharged pastures quickly and the next climatic determination would be La Nina persistence into next season, he said.

“If La Nina recurs, what might I do differently to get a good buffer of feed to carry through?”

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