March / April 2023 Certification and Education

George Brenn’s IAH Study Guide

George Brenn, Four Seasons Landscaping Nursery, created this study guide to help teach the material covered in the IAH Manual. His intentionw as to assist those trying to master the subjects within the manual.

I. pH, Acidity and Alkalinity

• pH is a measure of the acidity or alkalinity of a substance, represented on a logarithmic scale ranging from 0 to 1

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• Soil pH is a characteristic that affects nutrient uptake based on each ion's tendency to dissolve in water.

• Soil pH can be modified over time by the addition of sulfur or lime, which respectively decrease or increase alkalinity and affect pH.

• pH affects nutrient availability in the soil.

• One of the most common nutrient deficiencies we observe in our area is Iron deficiency, and is referred to as Iron Chlorosis. It is common because most of our soils were derived from limestone (= Calcium Carbonate) which would have a naturally elevated pH. Per the chart to the left, you can see that as the pH increases beyond 7, the availability of Iron decreases dramatically. Since Iron’s role in plant metabolism is in Chlorophyll synthesis and the “light reaction” in photosynthesis, the symptoms of an Iron deficiency are yellowing of the leaf margin. This is especially pronounced in Ericaceous plants, as well as Pin Oak, Birches, Oxydendron and Nyssa, plus others.

II. Soil Testing

• Soil testing is the only certain way to know the status of nutrients in the soil.

• Sample collection is critical, and it is necessary to consider "logical areas" to gather samples.

• Soil test results show existing levels of P, K, Ca & Mg, plus pH, CEC, and O.M.

• Nitrogen is not tested because it is readily leached, and recommendations are based on crop requirements.

• CEC values are important to note and provide indication of the soil's texture.

• Soil testing for container media (potting mixes) is different from ordinary soil testing.