Growers can give themselves a head start for next season by adhering to some basic practices when it comes to retaining seed from this year’s harvest.
SA Research & Development Institute research leader Dr Nigel Wilhelm, who did his PhD in trace elements and has been involved in numerous GRDC-funded nutrient projects, said larger seeds with high nutrient content supported better growth in young seedlings.
For growers with varying soil types across their farm, he said the seeds they keep for next year need to come from crops that were grown on more fertile soils.
However, not all growers will have soils with high fertility and Dr Wilhelm says one option is to boost the seed nutrient content artificially.
“One option is to buy in seed from different soil types, but the problem with that is the potential to bring in weed seeds and it is expensive,” he said. “Another solution is to boost the nutrient levels of seeds in home-grown crops with a very late application of trace elements to the crop, in particular manganese (Mn) and zinc (Zn).
“If you know or you are worried that you’re only getting low Mn and Zn levels in the grain, that indicates that the soil type it’s growing on is not very good. Boosting Mn and Zn levels will help retained seed to germinate and establish more vigorously next season.”
Generally, seedlings deficient of trace elements are weaker and less vigorous. Specifically, Dr Wilhelm said Mn and Zn play a role in the defence mechanisms of young seedlings against diseases such as rhizoctonia.
“Avoiding deficiencies early can help plants fight off the ravages of rhizoctonia and I think that’s a real benefit of getting seed that’s rich in Mn and Zn,” he said. “Deficiencies of either will also restrict root growth, which is something growers need to avoid.”
Dr Wilhelm said the optimum timing for such an application was during grain fill, or any time from a week after flowering to the milky dough stage.
“For many that’s an awkward time to get onto the crop – they might have clearance issues with boom sprays and are worried about running down the crop,” he said. “One technique could be to use a mister and do laps around the outside of the paddock. That’s a way of getting application out without trampling the crop itself. It is effective and a way of priming the seed for next year’s crop.”
The focus for growers should be on Mn and Zn because there was too great a risk of burning the crop with the application of other trace elements such as copper, Dr Wilhelm said. He said there was not strong evidence that applying phosphorus during grain fill made a difference to nutrient levels.
But Dr Wilhelm said there needed to be adequate green leaf area for there to be sufficient uptake of any applied nutrients. Clearly, this will not be possible for growers who have started harvest or who are experiencing a dry finish to the season. However, growers still had the option of retaining seed from better soils.
Being more stringent at seed grading by adjusting sieves to screen for smaller seeds was also worthwhile, Dr Wilhelm said.
“Another option growers could consider is seed dressing,” he said. “The seed you’re going to use next year can be coated with dressing that supplies the trace elements required to give it a good start. There are quite a lot of dressings around that can give young seedlings access to the required nutrients.
“Dressing is quite an efficient system and does a similar thing to loading seed with nutrients in the prior season.”
The choice growers made in boosting nutrients – either with a late application of trace elements or through seed dressing – came down to growers’ personal preferences and work plans, but both had their own advantages.
“Seed dressing would mean the retained seed would end up with a richer supply of nutrients for germinating seed, but the late spray is something that growers can get out of the way early and not worry about the following year – the seed is treated and can be stored easily,” Dr Wilhelm said. “There can be an issue in storing micro nutrient-dressed seed for too long, but it really comes down to what fits in your work plan.”
Dr Nigel Wilhelm, SARDI, firstname.lastname@example.org