Legumes lift dry management
GroundCover™ Issue: 138 January - February 2019 | Author: Clarisa Collis
Legumes are changing the face of the cropping landscape in low-rainfall farming systems across north-west Victoria. In the state’s Mallee region many bare, long-fallow paddocks have given way to a leafy mix of legume crops, such as vetch or field peas, which are mostly desiccated just after flowering for brown manure or cut for hay in early spring.
Driving this sequencing-shift are the strategic benefits of growing a legume break crop in rotation: fixed soil nitrogen, reduced disease pressure and improved control of grass and herbicide-resistant weeds.
Measuring these legume benefits against traditional crop rotations in the Victorian Mallee – specifically wheat/fallow or wheat/barley/fallow – are the findings of a three-year GRDC-invested study led by Jarrod Brown from AGRIvision Consultants.
“By showing growers how to implement a cost-effective pulse crop in rotation there is potential to save money on nitrogen fertiliser inputs and help manage seasonal risk,” Mr Brown says.
The consultant, based in Swan Hill, Victoria, says Mallee growers generally apply 40 kilograms of nitrogen per hectare, priced at $1.20/kg or $48/ha, to cereals on at least 70 per cent of their cropping country.
To help reduce this expenditure with legume-fixed soil nitrogen and determine the overall cost–benefits of legume break crops, the project examined the impacts of growing vetch, field peas and faba beans as part of a three-year crop rotation from 2015 to 2017.
The trials at Ouyen, Victoria, also looked at the rotational impacts of managing these legume break crops for different end uses: grain, hay and green and brown manure.
More specifically, the first year of the study in 2015 saw trial plots sown to field peas, vetch and faba beans, which were grown and managed for green manure, brown manure and grain. The first year also included a fallow treatment. Adjoining areas of the same trial site were also sown to wheat that year. The second year of the study in 2016 saw all the trial plots sown to wheat. And in the third year of the study in 2017 all the trial plots were sown to barley.
This series of different treatments allowed researchers to compare the effects of the different pulse crops grown and different approaches to their management on the following crops grown in rotation.
The first year of the trials in 2015 showed vetch and field peas managed for hay production were the most profitable rotation options for that growing season, with gross margin returns of $227/ha and $223/ha respectively.
Helping to achieve this profitability, vetch and field peas cut for hay were also the most productive crop enterprises in the 2015 season, yielding 2.2 and 3.3 tonnes per hectare respectively. The trials showed total expenditure on implementing vetch and field pea hay was about $216/ha and $273/ha respectively, which covered the costs of sowing, seed, herbicide, cutting and baling, fallow spraying and additional summer spraying.
But a slightly different picture of legume break crop profitability emerged when researchers examined the gross margin returns accumulated over three years of a rotation.
Looking at the cost–benefits over two seasons where legume/wheat, wheat/wheat and fallow/wheat were grown in rotation, the study showed the most profitable sequence was where legumes were cut for hay in 2015, followed by wheat in 2016. For example, a vetch hay/wheat rotation and a field pea hay/wheat rotation returned a cumulative gross margin of $869/ha and $825/ha respectively.
Wheat/wheat and fallow/wheat sequences were less lucrative, providing cumulative gross margins of $715/ha and $700/ha respectively.
Examining the cost–benefits of a three-year rotation, however, researchers found it was more profitable to grow three consecutive cereals (wheat/wheat/barley) compared with a legume followed by two cereals (legume/wheat/barley).
On average, growing three cereals in sequence returned a cumulative gross margin of $1050/ha, but adding a legume to this three-year rotation returned about $915/ha.
“A cereal-only rotation was more profitable than a rotation including a legume even though a quarter of the legumes performed better than cereals over three seasons.”
This is because the high total cost of managing a legume for grain, hay or manure saw a negative return on investment by the third year of the crop rotation.
Mr Brown says the trials further showed there was no significant difference in terms of soil nitrogen (nitrate NO3-N), soil moisture, disease pressure and weed pressure between the different rotations and crop management regimes. However, soil nitrogen and moisture, and disease and weed pressure are generally important considerations as part of an overarching farm systems approach to legume management.
Jarrod Brown, 0427 921 666
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