Better efficiency for pasture inputs

Jack England presenting to livestock producers at Donnybrook in March

Cropping and horticulture industries are familiar with precision agriculture (PA), but is there a case for it in the livestock sector?

South Australian livestock producer Jack England certainly thinks so. Jack was awarded a Nuffield Scholarship in 2016 to investigate how variable rate fertiliser use can be applied to livestock businesses. Producers from the South West got to hear about Jack’s experiences this year when he was invited to livestock forums held by the WA Livestock Research Council (WALRC).

Jack believes that livestock producers are over-fertilising less productive areas and under-fertilising better areas. The problem is that stock tend to concentrate grazing in certain areas, taking up or harvesting more nutrients from these areas compared to under-grazed areas. One reason for variation in grazing intensity is pasture quality, which can be affected by weed and species composition and growth stage.

“You need to know these areas because they aren’t getting the same harvest as preferred pastures, so don’t need replacement fertiliser,” Jack said.

This variation in pasture harvest can also play out at a paddock-scale.

“If one paddock has a higher carrying capacity compared to another and is getting more grazing days, preferentially feed it because you are removing more phosphorus,” Jack said.

Preferential grazing leading to higher variation in nutrient harvest is more common in set-stocking systems where grazing pressure is typically lower compared to rotational grazing.

But it’s not just about harvest. Stock, particularly sheep, tend to set up camps where they excrete and concentrate higher levels of nutrients.

“The bigger the paddock, the more time stock have to set up camps. The more you can increase grazing pressure in a rotation you don’t see the effect as much.”

Soil sampling procedures are designed to avoid stock camps, which are considered unrepresentative of the rest of the paddock. But the problem is that fertiliser may still be applied to these areas. Jack sees this as not only a waste of money, but also poor management of a finite resource and the surrounding environment.

“These camps don’t need fertilizer for ten years. Put it in productive areas and grow more grass. Less input costs and make more money.”

One of the best ways to identify areas of preferential grazing and areas of concentrated excrement is to track animals with a few GPS collars and then check to confirm that they are eating pasture in those areas.

“GPS collars show that sheep move phosphorus from valleys where they graze up to camps. Collars cost about $100. Find your stock camps and tell your contractor not to spread there.”

It is also important to recognize the difference in nutrient assimilation between different classes of stock.

“If stock are young and growing they will assimilate more phosphorus compared to mature stock which tend to relocate it within the paddock. So if you wean in the same paddock year after year, soil test that paddock to see what has been removed. Otherwise you might be penalizing your production,” Jack explained.

Jack has taken his system to the next extreme, targeting paddocks with deeper soils and distinct variation in pasture growth with grid-based soil testing in two-hectare sections every five years.  But he believes most famers already know a lot of the variation in their paddocks and can start to map zones of grazing intensity and nutrient excrement. This will help to plan smaller scale soil or plant-tissue sampling to calculate zonal rates, rather than relying on a single paddock test.

“My original soil transect went across two zones, one with Colwell P at 35 (mg/kg) and one at 15. My target Colwell phosphorus was 33, so by only applying to the low site I grew more grass. In other zones I might give 20% less or 20% more. I have reduced phosphorus by 30% in some areas,” Jack added.

To increase his confidence in soil test results and prescriptions, Jack uses nutrient rich strips on very small areas to see whether higher rates would increase yield.

For Jack, applying fertiliser in a more efficient manner will not only help realise agronomic potential and reduce fertiliser costs, but also conserve resources and minimise environmental impacts.

“Growing more with less is an obvious progression and evolution for farmers,” he concluded.

You can access Jack’s Nuffield Scholarship report by clicking here.


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