By GRDC western regional panel deputy chairman Dr Mike Ewing
Monitoring crops for micronutrient levels this month could be a valuable strategy to set up optimal yields in future years, especially where lime has recently been applied.
Research is showing that increased lime use across WA is affecting micronutrient concentrations in crop plants and changing the residual value of these nutrients on acid soils.
To assess the micronutrient status of cereal crops, samples of flag leaves are the best bet for tissue testing analysis.
Researchers Ross Brennan and Craig Scanlan, from the Grains Research and Development Corporation’s (GRDC) More Profit from Crop Nutrition (MPCN) program, say tissue testing will be particularly beneficial where:
- Lime has been applied in recent years on soils that were low or marginal for manganese (Mn) and zinc (Zn)
- Soils have been deficient in micronutrients and no micronutrients have been applied for 15 years or more
- Mn has not been applied on forest gravel areas
Plant requirements for micronutrients are affected by a range of factors, mainly crop species/variety and nitrogen (N) supply.
Previous WA research into the residual effects of copper (Cu), Zn, Mn and molybdenum (Mo) fertilisers, mainly for the cereal phase of the cropping rotation, has recommended relatively long periods between re-application of these micronutrients.
This has increased the probability that concentrations in crop plant tissue (whole shoots or youngest emerged leaves) are not being adequately monitored, potentially leading to situations where levels are low enough to limit grain production.
Dr Brennan, of the Department of Agriculture and Food WA (DAFWA), says the MPCN team is also finding that liming on acid soils reduces Cu, Zn and Mn concentrations but increases Mo in crop plants and can change the residual value of micronutrients.
He says at this stage of the season, and right up to flowering, Cu can be sprayed to improve pollination in an otherwise Cu-deficient cereal crop.
Trials set up through the GRDC-funded ‘WA Micronutrient: West’ project in 2014 showed foliar applications were not as effective as soil-applied Cu, so it is still important to follow-up with a soil application for next year’s crops.
Dr Brennan says it is now too late to use foliar sprays to address Zn and Mn deficiencies for this year’s grain production in WA.
But he stresses that tissue testing the 2015 crop can provide a good indication of micronutrient requirements for next year.
Dr Brennan says, when planning for 2016, growers should note that early season foliar sprays and liquid micronutrients have proved to be highly effective in correcting micronutrient deficiencies.
He says foliar application of micronutrients provides an immediate response where a deficiency has been observed (with visual symptoms) or diagnosed by plant analysis.
If a crop is diagnosed as deficient after seeding, the optimum time to apply foliar sprays depends on the particular micronutrient.
Dr Brennan says, although micronutrient applications to young crops will have some wastage - as a portion of the spray will be applied to the soil rather than the plant leaves, correction of the deficiency is usually required early in plant growth.
This will provide better potential for reaching optimal grain yield than sprays applied later in the crop cycle.
Dr Brennan has recently updated the MyCrop website to assist with diagnosing micronutrient deficiencies.
This information hub also outlines the recommended minimum plant micronutrient levels from tissue sampling for cereal, pulse and canola crops at various growth stages.
Other useful resources outlining micronutrient sampling guidelines and critical levels to help with deficiency diagnosis, analysis and decision-making include:
Dr Ross Brennan, DAFWA
08 9892 8444
Dr Mike Ewing, GRDC western panel
0409 116 750
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code
DAW00239, DAW00222, DAW00223