Avocado Leaf and Soil Tests Interpretation

1. Avocado Leaf and Soil Tests Interpretation By Lindsay Heard Brenmark Horticultural Consultants

2. Avocado Leaf and Soil Tests • Nutrient status - Nutrient corrections -Trends • Soil Texture Light Soils – Ash Pumice • Nutrient Leaching – High in light soils • High Cropload Trees; Nitrogen, Potassium, Boron • Nutrient deficiencies – Limiting Production • Phytophthora Control • Healthy Roots – Good nutrient uptake • Irrigation or Mulch – Increased root growth

3. Soil pH (Potential Hydrogen) • Reference to Acidity or Alkalinity • Soil pH 5.0 is 10 times acidic as pH 6.0 • Soil pH below 7.0 pH - Acidic • Soil pH above 7.0pH - Alkaline • Soil pH range Avocados 6.2-6.5pH • Lime Calcium Carbonate – Increase soil pH • Lime slow to increase soil pH • Fine particle size – increase soil pH quickly • Gypsum (Calcium Sulphate) - Neutral - Will not increase pH

4. Nitrogen Leaf – Shoot growth Chlorophyll (leaf greening) Role for synthesis of plant hormones Target Leaf Levels Autumn N 2.6-3.0% 2011 Autumn Leaf N Higher compared to 2010: N 2.7-3.0% Avoid excess N – high tree vigor – decreased fruiting – especially young avocados 4-6Yrs

5. Available Nitrogen N Soil Tests Snap shot of Nitrogen soil level Subject to soil moisture – plant growth rates High Available N level over dry summer Low soil moisture - low bacteria - microbe activity - Increased Available N soil level Good soil moisture - High grass growth - soil bacteria will use Available N in soil Long grass – low available N used – Available N increases over low rainfall summer months NZ Organic Matter soil levels 5 -10% High composting at soil surface

6. Available Nitrogen N Soil Tests Organic Apples – Hawkesbay Observation: Long grass in late summer resulted in Nitrogen Spike - High Vegetative - Shoot growth Organic Matter soil levels – high composting – Soil Bacteria using Available N Lowest available N levels BOP – Irrigated Avocados Good soil moisture – Available N used by bacteria and absorbed by roots Available N used by soil bacteria to breakdown bark (high carbon) and organic matter NZ Organic Matter soil levels 5 -10%

7. Cation Exchange Capacity CEC Number of sites in soil for cations to attach;- Potassium (K), Calcium (Ca), Magnesium (Mg), Sodium (Na) Organic Matter increases CEC levels Low CEC soils (8-15 CEC) Pumice Vocanic Ash – South of Te Puke Low CEC soils apply fertilisers on little and often basis – high leaching factor High CEC (20-30 CEC) – Volcanic Loam - Clay – Peat soils High capacity for nutrients to be applied and retained

8. Volume Weight (Vol/Wgt)- Bulk Density Is weight of a known volume of air-dried and ground soil. Provides indication of physical characteristics Low Vol/Wgt soils (0.6-0.7) Pumice Ash Soils – South of Te Puke Low Vol/Wght soils - apply fertilisers on little and often basis - high leaching factor High Vol/Wght (0.7-1.0): Clay - Silt Loam - Sandy Soils soils Clay – Silt Loams Vol/Wgt: High capacity for nutrients to be applied and retained

9. Boron • Pollen vigor – pollen viability • Monitor Leaf and Soil Boron trends • Apply Boron in February - Start of high root growth period • Apply Boron onto leaf or bark mulch • Boron subject to leaching in high rainfall climates • Solubor 21% B - Granubor (Borax Pentahydrate) 14.5%B • Granular Boron - Calcium Oxide Boron 10-14.0% B • Boron Foliar Applications – Apply if leaf B 35ppm or below. • Low Boron uptake by Zutano rootstock • Dusa Rootstock - Good Boron uptake - caution for Boron rates

10. Boron Leaf Levels

11. Boron Soil Levels

16. Thank You • Questions • Lindsay Heard Brenmark Horticultural Consultants