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Importance of Soil and Leaf Testing for Optimal Avocado Growth in NZ Regions

Soil and leaf testing are crucial for enhancing avocado growth in New Zealand, as soil types and fertility vary across regions. In Bay of Plenty, fertile ash soils with high organic matter contrast with the lighter soils of the Far North. Testing assists in identifying soil fertility, pH, and nutrient deficiencies, enabling corrective measures. For optimal avocado health, specific nutrient levels should be maintained, supported by leaf testing to validate nutritional programs. Regular monitoring ensures sustainable crop loading and tree health throughout the growing season.

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Importance of Soil and Leaf Testing for Optimal Avocado Growth in NZ Regions

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  1. Soil and Leaf Testing – WHY? NZ Soils • Soil types and behaviour varies widely between regions • BOP: Fertile ash soils with higher OM (15-20%) CEC >25 • Mid-North, South Auckland: Higher clay content soils, a varied OM (10-20%) CEC 20-25 • Far North and EBOP: Lighter, less fertile soils with lower OM (5-10%) CEC <20 as low as 5

  2. Soil and Leaf Testing – WHY? Soil test • Greatest value is in : • An important starting point • Lifting soil fertility on new blocks • the opportunity to correcting downward trends on mature blocks • Primarily pH, Base fertility, and phosphate • But also detection of gross deficiency (or excess)

  3. Soil and Leaf Testing – WHY? Soil test • Optimal soil levels are useful as a point of reference, • But, avocados produce well under a range of soil types and fertility • Provide “snapshot value” only for the more soluble nutrients eg K

  4. Optimal Levels Soil • pH 5.8-6.4 • Phosphate OlsenP(mg/L) >50 • CEC (me/100g) 20+ • Total BS % 70-90 • K BS % 6-10 • Ca BS % 55-65 • Mg BS % 12-15 • Zinc (Mehlich 3) mg/L 5-15 • Boron (Mehlich 3) mg/L 2-6

  5. Some Soil Test Specifics Cation Exchange Capacity and Base Saturation • CEC: the capacity of the (negatively charged) soil particles to retain nutrient cations and exchange them in the soil solution • Key Cations are Ca, Mg, K (also consider Ammonium, Boron) • Base Saturation: The extent to which we have utilised those exchange sites

  6. Typical Response to Base Application: Productive, young Orchard on Maniatutu Rd (EBOP coastal hills ie. light, low CEC, pumice soils) 2010: K: 2.7% Ca: 44% , Mg:6.3% pH: 5.9 Applied in the winter 2010: 2000kg/ha aglime 250kg/ha MgO, 250kg/ha Gypsum 2011: K: 3.2% Ca: 50% , Mg:12.0% pH: 6.1 Total Base saturation went from 53% to 66% Missed opportunity: No P applied and Olsen P dropped from 47mg/L to 39mg/L

  7. Calcium and Phytophthora Calcium is a key component of the fight against P.c. for 2 reasons • Root cell wall structure/strength • A natural fungicide as limits sporangial production and size

  8. Soil and Leaf Testing – WHY? Leaf Test • Our most valuable validation tool • Has our nutritional program succeeded in achieving optimal leaf nutrient levels? • Optimum levels are essential to the advisor as a point of reference • Weakness : At a given point with no emphasis on maintenance

  9. Optimal Levels Leaf % • Nitrogen2.7-2.9 • Phosphorous 0.16-0.19 • Potassium 1.1-1.2 • Calcium 1.5+ • Magnesium 0.4-0.8 • Iron 50-200 • Manganese (ppm) 150-300 • Zinc (ppm) 35-50 • Boron (ppm) 50-60

  10. Leaf Test Specifics • Mg: Magnesium oxide (x1) or Kieserite (x2) is sufficient in meeting magnesium requirement • Mn: Deficiency common in the FN and starting to appear from Auckland South. Easily visually identified and rectified using Manganese sulphate as a soil application along with a buffered foliar product such as Wuxal Manganese or Mantrac both at 1-2 l/ha applied 2-3x during the growing season • Zn: Zinc trunk drench of zinc sulphate heptahydrate or banded ZS monohydrate

  11. Winter Fertilisation • N and K are the key nutrients to be applying over the winter • Nitrate (vs Ammonium) is most available to the plant in low soil temperature but also easily leached , so • Little and Often is best • Also recommend a program of monthly foliar boron starting now (Solubor at 80g per 100litres) especially if autumn leaf boron is <30 • And a reputable proprietary foliar seaweed

  12. Other Factors • Crop Loading • Tree Health • Pruning

  13. Morton Rd Soil 2010 Morton Rd 2010

  14. Morton Rd Leaf 2010

  15. Morton Rd Soil 2011 Morton Rd 2010 Morton Rd Soil 2011

  16. Morton Rd Leaf 2011

  17. Morton Rd 2010 Omokoroa Soil 2011

  18. Omokoroa Leaf 2011

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