November 2013 CROP NUTRITION FACT SHEET NORTHERN, SOUTHERN AND WESTERN REGIONS MICRONUTRIENTS Micronutrient deficiencies can be tricky to diagnose and treat. By knowing your soil type, considering crop requirements and the season, and supporting this knowledge with diagnostic tools and strategies, effective management is possible. PHOTO: MATTHEW PHOTO: MATTHEW KEY POINTS Micronutrient deficiencies are best determined by looking at the overall W situation: region, soil type, season, ITNEY crop and past fertiliser management. Soil type is useful in deducing the risk of micronutrient deficiencies. Tissue testing is the best way to accurately diagnose a suspected micronutrient deficiency. When tissue testing, sample the appropriate tissues at the right time. Plant nutrient status varies according to the plant’s age, variety and weather conditions. The difference between deficient and This zinc trial shows the plot on the left with zinc compared to no zinc on the right. Zinc adequate (or toxic) levels of some deficiency appears as a lesion and a chlorosis between the veins of new leaves, producing micronutrients can be very small. a banding appearance. Leaf and plant growth become stunted with increasing severity of When applying fertiliser to treat the deficiency, and leaves eventually die and fall off the plant. a suspected deficiency, leave a strip untreated. Either a visual (B), copper (Cu), manganese (Mn), Traditionally, cultivation distributed these response or tissue testing can molybdenum (Mo) and zinc (Zn). micronutrients through the topsoil but the allow you to confirm whether the Iron (Fe) can be important, especially on introduction of no-till and one-pass seeding micronutrient was limiting. strongly alkaline soils. Other micronutrients equipment has led to more limited are also important for particular plants in physical distribution. particular situations. Introduction A recent study undertaken by the International Crop demand and uptake Micronutrients are essential for healthy Plant Nutrition Institute (IPNI) on behalf of the plant growth. The key challenge is accurate Different crop species have different GRDC found that zinc deficiency is a major identification of deficiencies and knowing micronutrient requirements and this can risk on soil types across all three cropping your risk level. be seen in the amount present in grain regions (northern, southern and western). (Table 1, page 2). Unlike the macronutrients such as nitrogen Copper deficiency is also a concern, (N), phosphorus (P), sulphur (S) and potassium although not as widespread as possible Even though the overall amount (K) micronutrients are only needed in small zinc deficiency. Copper and zinc are of micronutrients in the soil may be quantities. Even so, they can limit production. immobile in the soil, so must be in the high, uptake and their removal depends The most likely limiting micronutrients to pathway of as many crop roots as possible on the amount available, which in turn Australian cropping systems are boron to be accessed by the plant. depends on the soil properties. Level 1, Tourism House | 40 Blackall Street, Barton ACT 2600 | PO Box 5367, Kingston ACT 2604 | T +61 2 6166 4500 | F +61 2 6166 4599 | E [email protected] | W www.grdc.com.au 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 A tissue test result of <0.03mg/kg Critical level for DTPA Cu soil test: alkaline soils. <0.2 to 0.4mg/kg indicates Mo deficiency. 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. west, and soils with a high OM tests for Mo are unreliable. 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 TITUTE S N micronutrient deficiency. I A major challenge is that we simply do not UTRITION have adequate critical interpretation criteria N for tissue testing for many micronutrients. LANT P 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 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.