Stubble grazing calculator predicts nutritional value for livestock

The nutritional value of crop stubble for grazing sheep has been reassessed for the first time in 25 years
Tanya Kilminster runs a mixed enterprise farm with Merino sheep with her husband Dean Butler in Bruce Rock, Western Australia

No more guess work as a new Stubble Grazing Calculator from the CSIRO can predict liveweight gain or loss in sheep based on their size, condition and reproductive status. The tool will help farmers review their practices to get the most benefit.

In a good season mixed enterprise farms earn their largest profits during a high-yielding harvest. However, running a livestock operation – typically sheep – provides an important hedge for farm finances.

By selling wool or sheep, they can help to spread business risk during inevitable drought years by providing an ongoing income stream when crops fail.

For a grain and Merino sheep farmer like Tanya Kilminster, located at Bruce Rock 250km east of Perth WA, effectively managing the feedbase of their livestock is an integral part of any mixed enterprise farmer’s job – one that’s complicated by decreasing rainfall.

“We know that the climate has changed – we can see it in our rainfall distribution, particularly our winter rainfall is decreasing.

“We understand that we are in a very variable climate and it’s about trying to capture opportunities and not have too many losses in the system,” Ms Kilminster said.

“Whilst I truly believe mixed enterprise farms can succeed in a low rainfall or variable climate, you still have to manage your stock really well and you cannot afford to not have enough feed on hand or over-graze paddocks.”

However, as a fourth-generation farmer operating a 4,600-hectare property, her family has seen massive changes in how they’ve operated over the past century.

Crop stubble (or crop residue) was once seen as on-farm waste – recycled back into the soil at best or burned at worst.

However, over the past few decades industry-wide attitudes towards the biomass that remains above ground following harvest have dramatically shifted.

Growers now see it as a valuable resource to maintain groundcover. It can prevent erosion of their valuable topsoil and trap soil moisture for future crops for longer.

While some 40 million tonnes of grain are typically harvested annually in Australia – with 51.5 million tonnes from this current season – a similar amount of crop stubble biomass is left in paddocks.

Crop stubble is a valuable on-farm resource, particularly for mixed enterprise farmers

The value to mixed enterprise farmers who both grow crops and raise livestock is twofold.

A farmer like Ms Kilminster – who grows wheat, barley, lupins and canola – also needs to consider the needs of the 2,000-3,500 sheep on her farm.

Knowing how to properly manage crop stubble, where sheep typically spend 20% of their time, can make or break the ability to maintain groundcover to support future crops, while also acting as a feed source for livestock.

“It’s such a fine balance in the 12-month cycle of running a sheep operation in terms of their nutritional requirements and trying to manage pastures and then crop residues, while at the same time trying to look after our soils for crops,” Tanya said.

However, the last large-scale assessment of crop stubble nutrients occurred almost 25 years ago.

Since then, farming practices, machinery and crops have changed. Climate change also threatens to increase the severity of droughts, putting economic pressure on farmers to maximise their on-farm resources.

Changing nutritional availability for livestock

New research funded by Meat & Livestock Australia and Australian Wool Innovation sought to address the changed circumstances of mixed enterprise farmers.

Lead by Dr Dean Thomas from CSIRO Agriculture and Food, a two-year project worked to quantify the value of modern crop stubbles in the face of the summer-autumn feed gap when they are a critical source of feed for sheep in the mixed farming regions.

“The recent drought highlighted the need for mixed enterprise farmers across Australia’s southern grain belt to both protect their natural capital and utilise it effectively,” Dr Thomas said.

“Maximising the efficient use of on-farm resources like crop stubble can protect their soil and pastures during droughts and help them bounce back quicker when droughts break.”

The research team found that on average around 20% of the seasonable feed-base comes from crop stubble.

While around 60% comes from green and dry pastures, and the remainder comes from forage crops, dual-purpose crops, perennial forage species, or supplementary feeding.

Crop stubbles therefore make up a large enough proportion of an animal’s energy intake, while providing an important opportunity for farmers to keep stock off their more fragile pasture paddocks over summer.

Yet farm machinery has significantly improved over the last few decades, and improvements in setting design and monitoring means that headers generally leave behind less grain at harvest.

The crops themselves have also changed, with canola becoming a much greater part of the national crop rotation.

“While improved machinery has increased harvest values, there is evidence of a negative impact in the nutritional value of what’s available for livestock to graze,” Dr Thomas explained.

“For instance, there has been a broad reduction in protein content of chaff, which now needs to be taken into account when managing diets and livestock performance.”

Furthermore, nitrogen content in cereal stubbles was found to have decreased by about 25% compared with previously reported values. Consequently, there may be an increased need for protein supplementation compared to historic requirements.

There is some good news for canola growers, though.

It’s estimated that on average around 20% of the seasonable feed-base comes from crop stubble

The increased use of chaff lines and chaff carts means that any unharvested canola seed, high in protein and energy, will be easier to find and more likely eaten.

However, large variability between crops types, flock and paddock sizes, and animal factors such ewe weight, condition score and stage of pregnancy have left farmers needing to guestimate the value of their crop stubble for their livestock.

Consequently, as part of their research the team have been developing a decision support tool called the Stubble Grazing Calculator for farmers to use when calculating the needs for their flocks.

Recalculating crop stubble inputs

CSIRO has actively worked towards developing a new technology called, the Stubble Grazing Calculator.

It is able to predict liveweight gain or loss in adult ewes based on their size, condition and reproductive status, the type and condition of crop stubble (wheat, barley or canola), and the provision of supplementary feed.

Dr Thomas said the calculator is fundamentally a scenario testing tool and is designed to assist farmers estimate the number of grazing days available to stock on stubbles based on conditions in their paddocks and guide their next steps.

“Maximising the efficient use of on-farm resources like crop stubble can protect their soil and pastures during droughts, which should help them recover quicker with greater productivity when droughts break,” Dr Thomas said.

This means farmers will be able to make better-informed sequential grazing strategies, resulting in better animal welfare and production outcomes.

“It’s all about making the sheep enterprise more profitable and smoothing out the lean times to minimise economic impacts on farm budgets,” he said.

For a mixed enterprise farmer like Tanya Kilminster, the development of the crop stubble calculator is welcome help.

“Farmers have basically been guessing on how long sheep should be grazing stubbles.

“Now the stubble calculator gives me that understanding of when crop stubbles no longer provide the nutritional value required and when to start feeding,” she said.

“You can better manage risks by having all of the information in front of you to make decisions before it becomes an emotive decision – that’s when it becomes really difficult.”

Further testing of the Stubble Grazing Calculator is now being planned to ensure that it is very shortly ready for widescale use by the industry.


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