Micronutrient management

Sulphate and compost amendment
Sulphate and compost amendment

In calcareous soils with high pH and carbonates levels it is very likely that some deficiencies appear. Availability of B, Fe, Cu, Zn or Mn is low at pH above 8. High levels of Calcium can have antagonist effects making Magnesium less available to the plant. The problem is that it is not possible to lower pH in a durable way in these soils and nutrients added in fertilizers are blocked in the soil. However, there are cheap and easy means to provide the plant with their requirements.

The strategy consists of creating a temporary micronutrient-rich and moderate pH localised area where the roots can extract the sufficient amounts to prevent any defficiency. This can be done in a yearly basis at a low cost by appling a mixture of compost and ferrous sulphate. I have done this at fall this year for third leaf trees. I bury a mixture of 1 liter of compost and 300 g of ferrous suphate with Mg and Mn. I did so, 20 cm deep half a meter away from the tree. It costs around 0,1 € per tree. The compost has significant amounts of N, K and Zn, which complements the fertilization of the orchard. You can see the composition of both the ingredients as shown in their respective labels.

Compost composition
Compost composition
Sulphate composition
Sulphate composition

There is a quicker way to correct defficiencies when they appear during the growing season. In the orchard that I planted in 2013, almost 10% of almond trees showed chlorosis symptoms, with yellow and small leaves, especially in the youngest part of the shots. The soil has a pH of 8.4 with 28% carbonates. I tried sprays with foliar fertilizers that contained mainly Fe and also Mn, Cu and Mg, but they did not work. I did not do anything else in first and second leaf trees. When growth was severely disrupted for some third leaf trees I decided to try a more aggressive strategy: soil application.

15 Augost. 1 month after soil treatment.
15 Augost. 2 weeks after soil treatment.

I prepared a mixture of compost with a fertilizer based on ferrous sulphate. I tried different rates from 0:1 to 10:1, and added water until saturation. I dug around the trunk of the young trees until the roots appeared. Then I poured one or two liters of this mixture, left it rinse and covered the trunk with soil again. The effect was the same for the 13 trees that I treated, regardless the rate of sulphate. After a week, acute toxicity appeared, leaves dried out and the tree became naked. However, the stem remained healthy and the terminal shots became green instead of yellow. New and healthy leaves developed. The trees progressively recovered and became as green as the healthy ones. The recipe is cheap: 10 liters of compost and 1 kg of ferrous sulphate with micronutrients. That is enough to treat 5 trees.

Tree treated 1 month before.
Tree treated 1 month before.

The mixture creates a localized micronutrient rich environment with lower pH. Micronutrient availability booms and shocks the plant temporarily. That shock is easily overcome and deficiencies are solved. No single tree has experienced detrimental effects after this treatment. I recommend this only for individual trees that do not respond to foliar applications.

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