The case for two-year breaks
Comparing yield performance of different broadleaf crop and pasture options as breaks in an intensive cereal phase is the focus of the crop-sequencing project on upper Eyre Peninsula, South Australia.
The trial is part of a GRDC-funded project, Profitable Crop Sequencing in Low-rainfall Areas of South-Eastern Australia, which also includes Mallee Sustainable Farming (see above story), Upper North Farming Systems, BCG and Central West Farming Systems.
The trial involved growing cereals and different break options in 2011 and 2012 (options listed in Table 1) then on 14 May 2013, wheat was sown across all treatments at 55 kilograms per hectare with 65kg/ha diammonium phosphate (DAP).
Plots sown with wheat or oats in 2012 were sown to Clearfield® variety Kord CL Plus in 2013 to address grass weed issues. Other plots were sown to Mace.
Minnipa Agricultural Centre research officer Suzie Holbery says the value of break phases in the rotation has been clearly observed in the trial.
Yield trends included:
- wheat yields that averaged 1.7 tonnes/ha (Kord CL Plus) after continuous cereals but went up to 2.9t/ha (Mace) following a two-year fallow;
- wheat in 2013 that, following a one-year legume in 2011, still yielded higher than a continuous cereal rotation, highlighting the continued yield benefit two years after a single break;
- wheat following canola in 2012 that averaged 0.28t/ha less than if the break had been medic, field peas or oats, regardless of the crop in 2011;
- canola yields after oats that were lower than canola after field peas or medic, due to a higher grass weed burden; and
- cutting canola for hay in 2012 instead of harvesting for grain increased the following wheat crop yields by up to 0.7t/ha.
“Despite very strong wheat yields in the first two years of the trial, disease and grassy weeds started to reduce performance of continuous wheat,” Ms Holbery says.
“However, wheat crops following two-year breaks produced gross margins several hundreds of dollars per hectare better than continuous wheat. One-year breaks have improved the following wheat performance, but weeds and root disease are still an issue.”
An economic analysis over the three years found continuous cereal cropping was the most profitable through 2011 and 2012 but in the third year (2013), the positive effects of break options gave much higher wheat yields than other combinations and caught or even passed the gross margin of continuous cereals.
Wheat following two years of fallow was the highest grossing option in 2013 at $558/ha compared with $152/ha for continuous wheat.
A two-year break of canola cut for hay following field peas for grain was the second-highest grossing at $550/ha.
The most profitable one-year break option was a field pea and canola mixture in 2011, which was grazed. It grossed $840/ha over the past three years.
Over the three-year period, three rotations grossed between $900/ha and $1006/ha including:
- canola (graze and grain) followed by oats, hay;
- oats, hay followed by medic (graze); and
- canola (grain) followed by oats (graze).
Each gross margin assumed the hay and grazing could be fully used.
In 2014, plots have been sown again to wheat, which will complete the four-year rotation for each of the 20 treatments. Any ongoing benefits of break treatment options in 2011 and 2012 will continue to be measured.
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Full trial results are available at:
GRDC Project Code DAS00119