Crop rotation research draws profitability map
A series of surprise trial findings with implications for crop-sequencing strategies have surfaced from a major new research project that aims to lift the productivity and profitability of northern farming systems.
Driving the project is analysis indicating about two-thirds of crop sequences in the northern grains region are falling short of their potential water use efficiency.
Now working to overturn this, and some of the misconceptions contributing to under-performance in farm systems management, is the GRDC-funded Northern Farming Systems Initiative.
Large in scale and scope, the five-year project is examining tactics, such as crop sequencing, to improve farm business performance through modifying and fine-tuning existing farming systems.
Here, Ground Cover explores the first year of research findings at the core trial site, comparing 38 systems on southern Queensland grower Lyn Brazil’s 3000-hectare property at Brookstead, with CSIRO farming systems scientist Dr Lindsay Bell.
Project leader Dr Bell says the preliminary findings of the trials with a focus on the 2015 winter grains season showed that early sowing wheat lifted yields in the cereal crop by about half a tonne per hectare.
However, he added that the increased risk of frost damage where the LongReach Gauntlet wheat variety was planted two weeks before the variety’s conventional sowing window could undermine this yield benefit.
Slightly reduced grain protein was another side effect of early sowing, but the negligible decline in quality did not downgrade the crop’s wheat classification, Dr Bell says.
In addition to the yield advantage observed in early-sown LongReach Gauntlet wheat, the research indicated that planting the cereal on 14 May instead of 2 June improved its water use efficiency (WUE).
“Our research showed a yield and water use efficiency benefit for an early-sown wheat, which is consistent with research findings further south, but frost risk and rainfall can be influential factors in achieving these outcomes,” Dr Bell says.
Compared with other winter crops – specifically canola, chickpeas, faba beans and field peas – studied in the first year of the long-term research, early-sown wheat had the highest yield and WUE, respectively measured at 6.1t/ha and 20.4 kilograms of grain per millimetre of water used.
This top WUE ranking was rivalled by the later-sown LongReach Gauntlet wheat at 18.5 kilograms of grain per millimetre of water used, PBA Warda faba beans at 17.3kg/mm, PBA HatTrick chickpeas and the Clearfield® canola variety 45Y82CL, both at 12.6kg/mm, and PBA Percy fieldpeas at just 8.9kg/mm.
Dr Bell says the project is also examining the economic value of WUE for different crops and crop sequences to determine their effects on subsequent fallow efficiency and conversion of rainfall into profit.
Putting a dollar value on returns per millimetre of rain for the WUE of each crop, Dr Bell says wheat’s performance was in the middle of the pack.
This is because returns from winter-crop WUE for the following crop in rotation were calculated based on two main factors – grain commodity prices averaged over 10 years and measurements of water uptake from the start of the preceding fallow period (on 1 May 2014) until after the subsequent summer fallow period (6 April 2016).
Dr Bell says that based on rain received before wheat was planted and soil water accumulated after it was harvested, the cereal returned a gross margin of $0.94 for every millimetre of rain per hectare.
Of the other winter crops investigated, WUE in faba beans provided the highest gross margin return at $1.35 for every millimetre of rain per hectare ($/ha/mm) in the following fallow period, suggesting it was the most profitable option in a crop sequencing strategy.
These high gross margins where faba beans were grown in rotation stem from the crop’s winning combination of high long-term average commodity prices and the lowest rate of water uptake from the soil profile, which was linked to relatively high WUE.
Chickpeas were also found to be a profitable sequencing option largely due to high commodity prices, but they were not as profitable as faba beans because they extracted an extra 20mm of water from the soil profile, leading to lower WUE. Chickpeas returned $1.29 for every millimetre of rain per hectare.
Counter to the popular idea that chickpeas conserve more soil moisture for the following summer crop than other winter cereal or oilseed crops, the research found the pulse’s uptake of water matched that of wheat and canola.
“Growers often report that chickpeas leave more water in the soil profile than other winter crops, but our study showed the legume can extract just as much water as wheat,” Dr Bell says.
He says a further unexpected finding with implications for crop sequencing strategies was that other legumes – faba beans and field peas – extracted the least water from the soil profile, reserving more moisture for subsequent crops in rotation.
“Despite high stubble loads after the high-yielding pulses, we also found they were less efficient at accumulating soil water for the subsequent fallow period compared with wheat,” Dr Bell says.
Nutrient give and take
Another surprise finding in the trials was that faba beans and chickpeas exported more nitrogen, sulfur and potassium than other winter crops, such as wheat and canola, over the winter grains season.
For example, faba beans and chickpeas respectively removed 160 kilograms of nitrogen per hectare and 125kg N/ha from the soil, while wheat, canola and field peas removed between 80 and 110kg N/ha.
As a consequence of this high rate of nutrient removal, soil nitrogen was 40 to 55kg/ha lower when faba beans and chickpeas were harvested compared with other winter crops. And despite high rates of mineralisation in the soil, nitrogen reserves were still 30kg N/ha lower than the other winter crops examined after the summer fallow period in April.
Dr Bell says the higher rates of nutrient removal observed in faba beans and chickpeas, in part, resulted from the high yields achieved in PBA Warda faba beans and PBA HatTrick chickpeas in the 2015 winter growing season.
Complementing the core trial site on the Brazil family’s property on the Darling Downs, the research project is now continuing to explore different approaches to farm systems management at another six regional sites across Queensland and New South Wales.
More information:Dr Lindsay Bell,
GRDC Project Code CSA00050