Micronutrients What should you be doing? Rob Norton Regional Director IPNI ANZ

Transcription

1 Micronutrients What should you be doing? Rob Norton Regional Director IPNI ANZ

2 Micronutrients ARE NOT miracle workers Follow the season Mg/Micros Assess N (& S) Look at P (& K) Get the soil right Clearly establish if the micros are limi1ng factors. Start at the bottom and work up

3 Micronutrients Required in low amounts by plants. Essen7al for healthy growth. Difficult to pick up in soil tests due to low quan77es in soil: Eg Zinc <0.5 mg/kg may be a cri7cal level Chemically difficult to measure Low therapeu7c index (low value close to normal or Boron (B) toxic eg Boron (HWS B <2mg/kg def, >5 mg/kg tox) Varia7on in crop suscep7bility Molybdenum (Mo) OTen by associa7on: Soil ph Waterlogging Soil type (geology) Copper (Cu) Iron (Fe) Manganese (Mn) Zinc (Zn) Chloride Nickel Silicon

4 Micronutrient Contents in Soils and Crop Removal Nutrient Soil Levels mg/kg Amoun t in Soil (/ha) Wheat Grain mg/kg Removal 4 t/ha (g/ha) Canola Grain mg/kg Removal 2.5 t/ha (g/ha) Boron kg 2 8 g g Copper kg 5 20 g 4 10 g Iron 10, t g g 200,000 Manganese t g g 10,000 Molybdenum kg <0.8 <0.8 Zinc kg g g Wheat values from NVT Grain assessment, Canola from Incitec Pivot long term site, kg Zn >5 years, 2 kg Cu > 10 years

5 Amount versus Availability Plants compete for nutrients with the soil it s a chemical jungle out there! Metallic ca7ons (Cu 2+, Fe 2+, Zn 2+, Mn 2+ ) immobile Soil chemistry changes the availability of metal ions. Soil ph is a big driver of these reac7ons. Change in ca7on valence (eg Cu +, Fe 3+ and Mn 3+ ) have quite different proper7es. As ph rises Fe 2+ Fe 3+ (insoluble) Same for Mn 2+ Mn 3+ as ph rises Mn 2+ increases *100 / ph unit. For Zn 2+ insoluble hydroxides and phosphates can form (Zn(OH) 2 ) Zn availability changes 100 fold for each ph unit change.

6 Soil Test Results DTPA Critical Values? ZINC <0.5 (ph, Clay, OM, P) COPPER <0.3 (OM, N, Clay, ph) MANGANESE <10? (ph)

7 Availability of micronutrients assess the situadon Factors influencing availability of micronutrients in soils Cu Fe Mn Zn B Mo ph > ** ++ ph < water-logged soil drought high humus content high P-content sand compaction low availability high +++

8 Soil types and micronutrient risk Soil Order Boron Copper Manganese Molybdenum Zinc Calcarosol Low Mod High + Low High Sodosol Mod Mod Low Low Mod Vertosol Low Uncertain High + Low High

9 Diagnosis of micronutrient deficiency Situa7ons (soil & season & crop) probably most reliable Soil tests for the reasons above soil tests tend to be unreliable Use DTPA (chela7ng agent) and the assayed eg DTPA Zn, cri7cal value crop dependant (around 0.5 mg/kg) No soil test for Fe or Mo. Use an ASPAC lab PLEASE!!!! Plant 7ssue tests Visual symptoms

10 Demand and uptake by plants Varia7on in responses to micronutrients Micronutrient Boron Copper Iron Manganese Molybdenum Zinc Susceptible Crops Legumes, Brassicas Oats, Sunflower, Lucerne. Canola tolerant Some Legumes, Cereals tolerant Oats, Legumes. Brassicas, Legumes. Cereals, Canola tolerant. Also aware of large intraspeficic varia7on in response Root growth paoerns, phytosiderophore expression (root exudates). Chickpea 50% more efficient than wheat in accessing Zn (Brennan et al. 2001, JPN) Liole informa7on on varia7on among out present wheat cv s. Gladius 21 mg/kg Zn, Yitpi 25 mg/kg Zn

11 Care in sampling for youngest mature leaf mid- Dllering B <2 mg/kg Cu <1.5 mg/kg Fe no cri7cal values established Mn <12 mg/kg Mo <0.1 mg/kg Zn <8 mg/kg Highly dependant on 7ssue and 7ming sampled some cri7cal levels are developed based on whole plants What 1ssue and 1me is the cri1cal value based on?

12 Tissue Test Results Tissue Timing Condi7ons

13 So where does that leave us? Diagnosis firstly by region and year and crop Copper/Zinc cereals, Boron canola. Suggest with deficiency symptoms Confirm with 7ssue tests Consider grain nutrient assessment Post- harvest but input for future planning (no data to support this approach!) If you decide to spray leave a strip out! How will you know if it worked or not? No supplement, plus supplement Soil test and maybe 7ssue test Get some grain analysed.