Ground Cover Supplement : GC Supplement - More profit from crop nutrition II
Micronutrients 19 EARLY DIAGNOSIS IMPORTANT TO CORRECT LOW COPPER Research in the west is homing in on micronutrients and the message is: act early as deficiencies such as copper must be corrected before flowering By Ross Brennan MICRONUTRIENTS MAY ONLY be required in small amounts, but they are important for crop growth and resilience so growers need to monitor for deficiencies and be prepared for early interventions before the damage is done. Many Australian soils are deficient in micronutrients, which can reduce grain yield, expose plants to environmental stressors such as frost, and undermine fertiliser decisions. For example, nitrogen fertiliser can be wasted if the levels of other macronutrients and micronutrients, such as potassium, phosphorus, copper, sulfur, zinc, manganese and molybdenum, are not adequate. GRDC-supported research by the Department of Agriculture and Food, Western Australia (DAFWA), through the GRDC's More Profit from Crop Nutrition II project is developing tools to diagnose and manage micronutrient deficiencies in WA's grain- growing regions. The research also has trial sites in southern Australia, co-supervised by Dr Nigel Wilhelm from the South Australian Research and Development Institute. TISSUE TESTING The WA project highlights the importance of tissue testing to monitor crop growth and performance, as grain yield losses can occur if micronutrient deficiencies go undiagnosed. Part of the project is looking at the calibration of soil copper levels to plant tissue levels, drawing on current research and historic micronutrient experiments. Previously, soil testing for all micronutrients, including copper, was considered unreliable, so this project is testing and evaluating past relationships between the soil test and grain yield. The project is in its third cropping cycle and is scheduled to run until mid-2017. The early seasons of trials showed that foliar sprays and solid and liquid micronutrient fertilisers were very effective at correcting copper deficiency. Copper deficiency is not as prevalent todayinWAasitwas20or30yearsago -- thanks to changing land management practices and previous repeat applications -- but when it does appear, it shows up around flowering or at head maturity. A diagnosis at this stage is too late for treatment as the damage to the crop is done and grain yield is drastically reduced, so the project is developing strategies for early intervention. EARLY DIAGNOSIS Copper deficiency shows up at head emergence as areas of pale, wilted plants with dying new leaves in an otherwise healthy, green crop but by this stage it is too late to treat the crop. Symptoms are often worse on sandy or gravelly soils, where root-pruning herbicides have been applied and sometimes in recently limed paddocks (lime-induced copper deficiency is not common in WA). Soil tests can provide a rough guide to soil copper status, but there is no guarantee a crop will be able to access these elements during key times of the growing season as this will depend on rainfall patterns, soil moisture profile and subsoil constraints. The most effective assessment is by using tissue analysis or a youngest emerged blade (YEB). YEB concentration levels below 1.5 milligrams per kilogram indicate copper deficiency. If you suspect a copper problem at the boot stage, take 25 to 50 flag leaves and have them analysed for copper or micronutrients in general. This allows enough time for results to come back and a copper foliar spray to be applied before flowering if a deficiency is found. Tissue tests at other times during the growing season may not allow deficiencies to be completely rectified during the same season, but plant testing remains an invaluable tool to guide micronutrient applications the following year. TREATMENT If an early tissue test indicates a copper deficiency, it can be applied at the same time as a liquid nitrogen application (for a single pass) or as a separate foliar spray. A foliar spray is the best way to fix a copper deficiency at booting stage (GS43 to GS49) -- copper is required for pollen formation so must be applied before flowering. While there is a range of products that can be used as a foliar spray to apply copper (including sulfates, chelates and copper oxychloride), the important factor is to ensure the correct amount of the micronutrient is applied. From an economic perspective, look for products that are the least expensive source per unit of micronutrient. Copper applied at 150 to 250 grams/ha of copper (not copper compound) in 50 to 100 litres of water as a foliar spray can effectively correct the deficiency. Copper should be sprayed in cool, cloudy conditions as bright sun and warm days can increase leaf burn, particularly if copper sulfate is the compound used. Although foliar sprays and liquid micronutrients are highly effective during the growing season to correct any micronutrient deficiencies, 10 per cent yield losses can still occur even when foliar sprays are used in-season after tissue tests have indicated deficient levels in plants. Foliar sprays correct copper deficiency in the current crop but will not rectify soil deficiency, so copper must be applied to the soil for long-term correction. Copper is immobile so topdressing will only make copper available to the plant when the topsoil is wet. Instead, mix it through the topsoil or drill it down with soil fertiliser to increase the chances of roots accessing the copper. The project is also examining application of micronutrients via seed dressing and a range of granular fertilisers, and has developed tools to diagnose and treat micronutrient deficiencies. See the MyCrop website (www.agric.wa.gov.au/mycrop). □ G RDC Research Code DAW00239 More information: Ross Brennan, DAFWA, 08 9892 8474, firstname.lastname@example.org A fact sheet on micronutrients and trace elements is available at: www.grdc.com.au/ GRDC-FS-CropNutrition-Micronutrients GROWER TIP If you suspect a copper problem at the booting stage, take 25 to 50 fag leaves and have them analysed for copper or micronutrients in general.
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