- A big gap exists between actual and achievable production yields per unit of water for many crops
- Adopting better agronomy can help to narrow the yield gap and boost crop and water productivity
- In some cases, yield gaps reflect a response to environments rather than inefficiencies
- Practices such as timely sowing, adequate plant nutrition, water management and pest and weed control have a big impact on crop yields
Associate Professor Victor Sadras inspects GRDC-
funded stubble and water retention trials in southern
Australia that are contributing to efforts to improve
crop and farm water use efficiency across the globe.
Available water is the biggest limitation to grain yields across the globe and new research shows Australia is not unique in having a significant gap between actual and achievable crop production per unit of water consumption.
For several years, the South Australian Research and Development Institute (SARDI) has led research into the yield gap issue through the GRDC-funded ‘Improving crop and farm water use efficiency in Australia’ project.
It is investigating the roles of plant breeding and agronomy in improving grain yields in low-rainfall environments – or, in other words, finding ways to get ‘more crop per drop’.
Recently this SARDI team, headed by Associate Professor Victor Sadras, collaborated in a global study of the water use efficiency (WUE) of major grain crops. This included five case studies ranging from subsistence to high-tech farm production systems.
The study was part of a United Nations Food and Agriculture Organization (FAO) ‘State of the world’s land and water resources for food and agriculture’ project.
Associate Professor Sadras says the aim was to indentify major regional and crop-specific factors that were constraining the water productivity of grain crops in a range of environments and compare this against benchmarks.
“To address pending water and land scarcity issues across the world, we need to find ways to close the gap between actual and attainable crop yields per unit of water consumption,” he says.
“And we need to be able to increase yields for the water available in any given season in any particular region of the globe.”
In Australia in the 1970s the benchmark WUE for wheat was 20 kilograms per hectare per millimetre of rain (as determined by an influential study by researchers Reg French and Jeff Schultz).
Associate Professor Sadras says on the back of technological and varietal improvements, this benchmark rose to 22kg/ha/mm in the early 2000s and – using the newest varieties – is now about 24kg/ha/mm. But he says many southern Australian cropping systems are up to 50 per cent below that new benchmark, at 10 to 12kg/ha/mm.
Associate Professor Sadras says while this seems quite low, it is relatively high compared to other nations in the FAO report.
The average rainfed wheat WUE in the China case study is 9.8kg/ha/mm, North American rainfed wheat is 8.9kg/ha/mm, rainfed wheat in the Mediterranean Basin is 7.6kg/ha/mm and 5.3kg/ha/mm in the South Central US Great Plains.
The FAO report, Status of water use efficiency for main crops, showed there was an average 56 per cent gap between actual and maximum yield potential in Australian cropping systems, which have an average WUE of 9.9kg/ha/mm. This is the same as the yield gap at the China and northern Great Plains sites in North America, but lower than the southern Great Plains site in North America at 68 per cent and Mediterranean Basin at 63 per cent.
Associate Professor Sadras says the main reason Australian grain producers operate below potential is the risk associated with applying nutrients, especially nitrogen.
“There is potential to close the gap and boost the performance of our crops, but a realistic aim is to target 80 per cent of the benchmark level,” he says.
“Improving WUE and the yield productivity of wheat crops requires adequate plant nutrition, good management, and balancing water use early and late in the season.
“We are finding in our research that water and nitrogen are critical early in the season – between stem elongation and flowering – and a range of crop sowing strategies can promote water retention and early plant growth.”
The FAO water scarcity report said optimising WUE in some farming systems required nitrogen rates that are too costly, risky or environmentally unsound. It said this is particularly important in areas with a high fertiliser-to-grain-price ratio.
Stemming from the FAO report and GRDC research to date, Associate Professor Sadras says it is apparent Australian researchers need to concentrate more closely on the interactions between water and nutrient availability and use.
“Similar to the study of WUE, we need to assess potential and actual nutrient use efficiency per unit of water available to crops,” he says.
On the east coast, trials have started to look at precisely how much nitrogen is needed to capture maximum benefits from summer rainfall.
Associate Professor Sadras says a deficiency of either water or nitrogen means neither will be used efficiently and if there is too much nitrogen, it is wasted. He says part of the solution is to also create closer synergies between crop breeders and agronomists earlier in the process of varietal selection and development.
This is backed by the conclusion of the FAO report, which said genetic improvements for WUE will contribute to higher grain yields but there are potentially bigger gains to be made from management practices that improve the capacity of crops to capture water in many regions.
“There is an obvious need for agronomic solutions to close the common, and often big, gap between actual and attainable yield per unit of water use demonstrated for all five case studies in this report,” the report said.
“Whereas genetic and agronomic solutions are not mutually exclusive, it has been argued that agronomic practices to narrow the gap between attainable and actual yield per unit water use are an effective investment of scarce R&D funds – particularly for smallholder farmers.
“The practices required to close the gap have some elements that seem to be widespread (across the globe) – such as timely sowing, effective control of weeds, arthropod pests and diseases and adequate fertilisation.
“As a rule for winter crops, timing the earliest sowing that is compatible with frost risk would maximize grain yield and water productivity in association with favourable temperature, radiation and humidity.”
Associate Professor Victor Sadras
08 8303 9661
The FAO report is available from the FAO website: Status of water use efficiency of main crops
Water Use Efficiency of grain crops in Australia: principles, benchmarks and management to order your booklet see page 3 of Ground Cover Direct catalogue or visit the GRDC Bookshop
Next: Women championed as agricultural science leaders
GRDC Project Code