with Brett Petersen
Kiwi Fertiliser & Golden Bay Dolomite
When I am asked to do soil sampling on orchards and gardens, I often find extreme variations in soil conditions. With avocados, the pH can often be over 7. When I test blueberry soil, the pH is mostly around 5. This is usually a target. Why do we have these extreme variations?
Well, pH should never be the cause of your fertility programme. It must be result of it. When the soil fertility is balanced, the pH will be correct. Do not aim at any figure. Aim to balance the soil with proper nutrients. Here is a partial example of local avocado soil analyses, from Perry Agricultural Laboratories in Missouri. These nutrients supply the most important readings relevant to pH. TEC 23, pH 7.1, OM 7.1, sulphate 70, calcium 90% (of base saturation) (+2,000 kg/ha), magnesium 4.4% (-400 kg/ha), potassium 1.0% (-1,100 kg/ha). The + or – figures are elemental, not product. What has caused the elevated pH? In this case it is extreme excess calcium that has driven down magnesium and potassium which are both extremely deficient.
Are the trees heathy and do they produce well? No. It is obvious that gypsum has been over applied. All nutrients need to be balanced for superior results. A very good sulphate reading will not achieve that on its own. Gypsum is fine if the circumstances suit, but you must know when to stop. It should only be applied when the soil measurements allow it. This is where we at Kiwi Fertiliser have the knowledge, technical training and subscribe to the right laboratory to provide the correct figures to calculate superior recommendations on.
Blueberries suffer at the other end of the pH scale. TEC 36, pH 5, OM 10.2, Sulphate 75, calcium 37% (-4450 kg/ha), magnesium 4.7% (-650 kg/ha), potassium 1.7% (-1550 kg/ha). In this case calcium and magnesium are extremely deficient and potassium is very deficient. Are the bushes healthy and produce well? No.
Do you as growers believe that the plants, whether avocados or blueberries like deficient/excess calcium, magnesium and potassium, to satisfy a man-made goal called pH? pH is the negative logarithm of the hydrogen ion. Does hydrogen supply nutrition? No. With the avocado, the exchangeable hydrogen is zero. The blueberries have more than 40 per cent. Avocados and blueberries respond to the same soil conditions. Please think about these things carefully. Don’t allow yourselves to be led by the nose. These figures are insane. They are costing you big money.