photo: Matthew Witney Different crop species have different species have different crop Different and this can requirements micronutrient in grain be seen in the amount present 1, page 2). (Table Even though the overall amount in the soil may be of micronutrients depends high, uptake and their removal on the amount available, which in turn depends on the soil properties. Traditionally, cultivation distributed these Traditionally, the topsoil but the through micronutrients of no-till and one-pass seeding introduction limited equipment has led to more physical distribution. demand and uptake Crop s stern region e This zinc trial shows the plot on the left with zinc compared to no zinc on the right. Zinc This zinc trial shows the plot on the left with zinc compared between the veins of new leaves, producing deficiency appears as a lesion and a chlorosis severity of become stunted with increasing a banding appearance. Leaf and plant growth the plant. fall off and leaves eventually die and the deficiency, (B), copper (Cu), manganese (Mn), molybdenum (Mo) and zinc (Zn). (Fe) can be important, especially on Iron alkaline soils. Other micronutrients strongly also important for particular plants in are particular situations. study undertaken by the InternationalA recent Plant Nutrition Institute (IPNI) on behalf of the GRDC found that zinc deficiency is a major cropping all three risk on soil types across (northern,regions southern and western). Copper deficiency is also a concern, as possible although not as widespread Copper and zinc are zinc deficiency. immobile in the soil, so must be in the as possible roots pathway of as many crop to be accessed by the plant.
When applying fertiliser to treat When applying fertiliser to treat leave a a suspected deficiency, Either a visual strip untreated. or tissue testing can response allow you to confirm whether the was limiting. micronutrient The difference between deficient and between The difference adequate (or toxic) levels of some can be very small. micronutrients When tissue testing, sample the tissues at the right time. appropriate Plant nutrient status varies according age, variety and to the plant’s weather conditions. Tissue to testing is the best way accurately diagnose a suspected deficiency. micronutrient Soil type is useful in deducing the deficiencies. risk of micronutrient Micronutrient deficiencies are best deficiencies are Micronutrient determined by looking at the overall soil type, season, situation: region, past fertiliser management. and crop
orthern, Southern and W KEY POINTS
Australian cropping systems are boron boron systems are Australian cropping The most likely limiting micronutrients to The most likely limiting micronutrients quantities. Even so, they can limit production. | W www.grdc.com.au [email protected] Barton ACT 2600 | PO Box 5367, Kingston ACT 2604 | T +61 2 6166 4500 | F +61 2 6166 4599 | E House | 40 Blackall Street, Level 1, Tourism (K) micronutrients are only needed in small are (K) micronutrients (N), phosphorus (P), sulphur (S) and potassium nlike the macronutrients such as nitrogen such as nitrogen Unlike the macronutrients your risk level. identification of deficiencies and knowing plant growth. The key challenge is accurate plant growth. Micronutrients are essential for healthy are Micronutrients Introduction management is possible. requirements and the season, and supporting this knowledge with diagnostic tools and strategies, effective knowledge with diagnostic tools and strategies, effective and the season, and supporting this requirements Micronutrient deficiencies can be tricky to diagnose and treat. By knowing your soil type, considering crop crop By knowing your soil type, considering treat. can be tricky to diagnose and deficiencies Micronutrient trients Micronu N Fact Sheet Fact
n Nutritio Crop November 2013 November Page 2
For example, even though there may be making some crops more susceptible to higher grain zinc content (25 milligrams/kg) 130 kilograms per hectare of zinc in the deficiencies than others (Table 2). Copper is than GladiusA (21mg/kg). soil, much of it may be unavailable and a good example: canola is far more efficient so is unable to meet the modest plant at accessing this nutrient than wheat. Diagnosis of deficiencies requirement of 0.1kg/ha in a wheat crop. Micronutrient concentration can also vary The overall situation – soil type + season + The differing requirements of various crops between cultivars. For example, when crop – is the most reliable indicator of the are often due to differences in root systems, grown on the same sites, YitpiA wheat had possibility of the deficiency. While soil tests
Micronutrients Table 1 Micronutrient concentration and crop removal in a 4t/ha wheat crop, a 2.5 t/ha canola crop and a 2.0t/ha lupin crop. For tissue testing in cereals take the youngest emerged leaf blade at mid- Wheat grain Removal Canola grain Removal Lupin content Removal Nutrient mg/kg 4t/ha (g/ha) mg/kg 2.5t/ha (g/ha) (mg/kg) 2.0t/ha (g/ha) tillering. (Copper can be sampled at the flag leaf stage). Boron 2 8 13 33 20 40 Copper 5 20 4 10 5 10 For canola, sample the youngest Manganese 44 176 49 125 40 800 fully emerged leaf. Molybdenum 0.2 0.8 0.3 0.8 2 4 Boron (B) Zinc 25 100 34 85 30 60 Tissue test results below 2 to 4mg/kg Source: Rob Norton, IPNI are marginal, values greater than 5 to Adequate supply under acidic and On very acidic soils, soil-applied 10mg/kg indicate B adequacy. wet, compacted heavy soils. Mo may not supply a wheat crop Critical level for hot water soluble Not readily leached. for the entire season. (HWS) B soil test: <0.5mg/kg. Long to very long residual availability Very small window between Zinc (Zn) of applied Cu (>15 years). deficiency and toxicity (0.5mg/kg A tissue test result of <10mg/kg to 5mg/kg) Manganese (Mn) indicates Zn deficiency. Deficiency most likely on acidic, A tissue test resulting in an Mn value Critical level for DTPA Zn soil test: sandy soil with low organic matter of <20mg/kg indicates a possible <0.2 to at least 0.4mg/kg, or even (OM), low pH and low water-holding deficiency, less than 10mg/kg is higher on alkaline clay soils. Critical capacity (WHC). almost certainly deficient. values vary with pH, clay content Deficiency can also appear and OM content. Critical levels for DTPA Mn soil test: after liming. <5mg/kg (but this is an unreliable Deficiency most likely on alkaline Very mobile and subject to leaching, test). sands with a high P concentration has limited residual availability. (high pH, low WHC). Deficiency most likely on well- Adequate supply is likely on alkaline, drained, alkaline and dry soils (high Deficiency can first appear as low OM soils. pH, low WHC). stunted, irregular growth and two-toning of leaves, followed by a Adequate supply most likely on acidic, Copper (Cu) lesion developing in the middle of waterlogged soils with high OM. Copper can be tested at the flag leaf the leaf. Leaf may ‘kink’ over. Can leach as Mn2+ or MnO2+. stage in cereals. A tissue test result Adequate supply most likely on of 1.3 to 1.6mg/kg indicates a mild Shorter residual availability than Cu. heavy, acidic, high OM soils. deficiency. <1.3mg/kg is moderately Molybdenum (Mo) Residual availability of applied zinc to severely deficient. is moderate (three to five years) on Critical level for DTPA Cu soil test: A tissue test result of <0.03mg/kg alkaline soils. indicates Mo deficiency. <0.2 to 0.4mg/kg Residual availability of applied zinc Critical level for CaCl Mo soil test: Deficiency most likely on alkaline 2 is >15 years on acid, low OM, and sandy soils in the south and <0.1mg/kg although like Mn, soil sandy soils. tests for Mo are unreliable. west, and soils with a high OM Zn stimulates root systems so concentration (high pH, low WHC, Deficiency most likely on acid sandy healthy levels can assist in fighting high OM). soils with poor P history (low pH, low diseases such as rhizoctonia. WHC). High sulfur supplies can also Early season Cu deficiency is If group B herbicides have been induce deficiencies. evidenced by ‘pig tailing’ (curling) used Zn strategy may need to be but may be temporary, due to dry Adequate supply on alkaline revisited. Some group Bs can lower conditions or large N applications. If heavy soils. levels of Zn uptake in the plant. deficiency is prolonged, heads may Frequently adequate where acid soils On soils with high levels of free go dark at the end of the season with have been limed to pH >4.8. Ca lime, more than one application grains missing from the head. Declines to around 50 per cent after may be needed. two years, depending on soil pH. Page 3
work best for macronutrients, tissue tests are the most robust method of identifying a micronutrient deficiency. A major challenge is that we simply do not have adequate critical interpretation criteria for tissue testing for many micronutrients.
Tissue testing Plant tissue testing is a more reliable method than soil testing for diagnosing and monitoring micronutrient status. It is essential to collect a proper sample photo: international P lant N utrition I n s titute photo: international for tissue testing. The distribution of micronutrients can be different in leaves, stems or whole plants. Boron is essential for growth and development of new cells. It is immobile in the plant, Plant nutrient status may also vary so deficiency symptoms will appear as abnormal growth on the youngest leaves. Boron- according to the age of the plant, the deficient canola can appear as deformed, curled and rough-skinned leaves with torn variety and the weather conditions. margins and yellow to brown spots in the interveinal area of the leaves. Tissue test samples can become contaminated if they come into contact and handle the samples very carefully to production in Western Australia in some with any other surface, such as skin, soil, ensure their integrity. seasons and adequate in others. The soil cars, etc. Always wear disposable gloves test values also change with soil types. For cereals, take the youngest emerged Table 2 Susceptibility of leaf blade at mid-tillering. Copper can be Note: there are no reliable soil tests for iron, different crops to micronutrient sampled for at the flag leaf stage, and if it manganese or molybdenum. deficiencies. is marginal in the youngest tissue it can be If you plan to use soil testing, choose a Micronutrient Susceptible crops applied as a foliar spray before flowering. laboratory accredited by the Australasian Soil Boron Legumes, brassicas For canola, sample the youngest fully and Plant Analysis Council (ASPAC). ASPAC Wheat, barley, sunflower, lucerne emerged leaf for diagnostic tissue testing. accreditation provides assurance that the lab Copper (canola tolerant) is proficient in the particular test you require. Detailed sampling procedures for each Iron Some legumes (cereals tolerant) You will find a list of certified labs on the crop, related to the optimum growth ASPAC website (see Useful Resources). Manganese Oats, legumes stage, can be obtained from fertiliser Molybdenum Brassicas, legumes companies, agribusiness personnel or Visual symptoms Zinc Oats, wheat, barley (canola tolerant) agricultural consultants. Visual symptoms can also be a guide, but Source: Rob Norton, IPNI be aware some symptoms may mimic Soil testing other unrelated problems. They may also In general, soil tests have a low reliability be temporary or transient due to cold in predicting micronutrient deficiencies weather, drought or slow root growth. because the elements are present in such For example, a copper deficiency in cereals low quantities. can resemble frost, take-all or drought, Analytical laboratories use a range of and even a molybdenum deficiency can chemicals to extract the micronutrients produce white heads. in soil to assess what is available to the plant. For example, DTPA is a common SoilMapp extractant and the critical value for DTPA CSIRO has developed an excellent app for extractable zinc can be as low as 0.2mg/kg iPads called SoilMapp, an Australian or less, depending on soil type. Obtaining soil database that allows users to learn reliable analytical results with such low about the likely soil types on their property soil concentrations requires careful soil or anywhere else in the country (see sampling and handling. photo: Matthew W itney photo: Matthew Useful Resources). Copper is a key element of In addition, a low soil test value may The app’s location service can be used to chlorophyll and plays a central role in be close to either a normal or toxic place you on the soil map so your particular soil photosynthesis, and deficiencies are value for that nutrient. For example, type can be identified. Once known, the risk of often associated with high organic hot water soluble (HWS) boron at less micronutrient deficiency can be assessed. matter soils. Early season deficiency is than 0.5mg/kg is considered a deficiency, evidenced by ‘pig tailing’. If deficiency while more than 5.0mg/kg is toxic. Effects of soil type is prolonged heads may go dark with Similarly, a DTPA manganese soil test value In the northern region, the main issue grains missing. of 3 to 4mg/kg may be deficient for lupin appears to be zinc on Kandosols, Vertosols Page 4 and Sodosols. There is uncertainty about have seen good results with fluid or liquid copper generally. in-furrow micronutrients.
In the south, Calcarosols, Sodosols and It is best to apply immobile nutrients to the Vertosols have high risk of zinc deficiency, most responsive crop; cereals respond while manganese deficiency is likely to be a better than oilseeds to zinc and copper significant risk on these soils if they contain application. Depending on the soil type, more than 60 per cent free calcium carbonate. annual applications may not be needed. In the western region Sodosols are the For nutrients with a lower residual activity major soil order and low zinc is seen on or where soils are likely to strongly these soils. However Kandosols and bind micronutrients, annual or tactical Tenosols are also more prevalent in the applications may be best. These can be west than in eastern states. in-furrow or in-crop foliar applications. nternational P lant N utrition I n s titute photo: I nternational Acidic soil types, such as the more strongly If a spray application of foliar fertiliser is to acidic Tenosols, are likely to be at risk be undertaken, leave a strip untreated. This of molybdenum deficiency. Manganese will allow you to determine whether it was deficiency is also moderately likely in the micronutrient that was limiting. Manganese is part of the plant’s enzyme Kandosols and Tenosols. For foliar applications to be effective, a systems. Deficiencies often occur on large plant leaf area is required to absorb high organic matter soils with neutral to Treatment the product. If applying to seedlings, alkaline pH and on those soils that are With immobile nutrients such as copper multiple applications may be necessary. naturally low in manganese. Manganese and zinc, physical distribution through the Post-harvest, grain nutrient testing can is immobile in the plant, so its deficiency appears as reduced or stunted growth soil is important to ensure roots interact be considered. This will not provide a with visual interveinal chlorosis on with placed fertiliser. conclusive guide to the risk of micronutrient younger leaves. Cereals can develop Smaller granules of fertiliser, more of them deficiency, but in conjunction with gray spots on their lower leaves, and and better placement, will be more effective information from the overall situation (crop, legumes can develop necrotic areas on than a fertiliser with larger granules, even season, soil type) it can be used to inform their cotyledons. if it is more concentrated. Some growers potential management decisions.
Useful Resources Further information project Codes
ASPAC Ross Brennan CSA00021, DAN00165, IPN00001 www.aspac-australasia.com DAFWA 08 9892 8474 Find a laboratory with comprehensive [email protected] ASPAC certification: www.aspac-australasia.com/index.php/ Robert Norton component/labproficiency IPNI 03 5381 2673 Better fertiliser decisions for [email protected] cropping systems in Australia www.bfdc.com.au Simon Speirs NSW DPI Fertcare® accreditation 0428 647 787 www.fertilizer.org.au [email protected] IPNI micronutrients presentation anz.ipni.net/article/ANZ-3181 Nigel Wilhelm SARDI SoilMapp 0407 185 501 www.csiro.au/soilmapp. [email protected]
Acknowledgements: Andy Bates, Bates Agricultural Consulting; Ross Brennan, DAFWA; Robert Norton, IPNI; Simon Speirs, NSW DPI; Mike Bell, QAAFI; Nigel Wilhelm, SARDI; Matthew Witney, Dodgshun Medlin.
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