Leading farming systems researcher Dr. Nigel Wilhelm from SARDI recently presented to young farmers from across Western Victoria on trouble shooting crop nutrition.
The BCG and Agriculture Victoria young farming discussions group meetings, better known as ‘GAPP’ (Growth, Adoption, Production and Profitability) were held last week and focused on crop nutrition, in particular the management of trace elements.
Visual symptoms of trace element deficiencies can be hard to spot and are often localised in the paddock due to lack of mobility in the soil and Dr. Wilhelm provided advice on how to inspect crops throughout the growing season, test for accurate diagnosis and treatment strategies.
“When you know what to look for you have an opportunity to manage appropriately,” he said.
“Zinc deficiency produces a very unique symptom in the cereals, in wheat it manifests itself as two pale strips down the young leaves. In barley, the same symptoms can be seen, but it isn’t as clear and may also show up as spots.”
Dr. Wilhelm added that oats, however, have a different symptom where the old leaves will turn purple.
Unlike zinc deficiency, copper can be very hard to detect, as it is always localised and can be seasonal dependent (will show up more in a dry spring). Plants with a copper deficiency can show textbook symptoms: tips withered, curled/twisted and dead. However in the field it is more likely to look like frost damage, with whitened or occasionally gaps in the head, but not in the areas of the crop where it would be expected for frost.
Manganese deficiency can make the crop ‘flop’ and it looks like the crop has been through a drought, even though the soil can be quite wet. Manganese can also produce pale green/yellow leaves and soil compaction can relieve the symptoms a little.
Conversely, iron deficiency symptoms are the opposite of manganese symptoms. Soil compaction exacerbate the problem, and crops will have canary yellow leaves compared to the pale green/yellow leaves with a manganese deficiency.
Because of the difficulty that can result from visual assessment alone, the best method for detecting trace element deficiencies is to use plant tissue testing of leaves, generally at early growth stages.
The advantage of most trace elements is they can stay in the soil for a long time before they are tied up. Dr Wilhelm explained that a soil application of zinc could last up five to seven years while copper could last up to ten years depending on soil type. One exception is iron. If it is applied to the soil, it can get tied up within weeks with the process being exacerbated by calcareous soils.
For maintaining zinc levels in the soil, Dr Wilhelm suggested that a method of applying approximately 0.5kg/ha every year or a bigger application of approximately 1kg/ha every five years.
GAPP participants discussed the pros and cons of the several zinc foliar spray products on the market. The best time to use a zinc foliar spray is early in the crop, around the 3-4 leaf stage. Once the crop starts showing symptoms of zinc deficiency it becomes hard to recover with a foliar spray.
If using a copper foliar spray on the other hand, it’s best to apply at a later stage, within four weeks of flowering. Care must be taken with a foliar spray as it can burn the crops. The use of seed coatings of copper is not recommended as it could be toxic to the seed even at low levels.
Foliar sprays are available for iron, however it may not be as effective due to iron’s lack of movement in the plant.
Throughout the season make sure you get out in the paddock and ask questions if you start seeing anything unusual.
This article was published in the Stock and Land on the 15 June.
Further reading can be found on the GRDC website.
