HOW SOIL CONDITIONS AFFECT MICRONUTRIENT ABSORPTION
Macronutrient fertilisers (NPK-fertilisers) are commonly given to plants as soil-added granules. The granules slowly break down in the soil, and the nutrients are absorbed through the plant’s roots.
With micronutrients, such as zinc and manganese, application through the soil can be affected by various soil conditions. The most effective method of increasing micronutrient content of plants is the combined application of nutrients through foliar fertilisation and soil fertilisation. However, in some cases soil conditions can bind the micronutrients into an unusable form. Some of these conditions are presented in this white paper.
SOIL TYPE, PH AND TEMPERATURE
If the soil composition is very light (e.g. sand), the micronutrients are easily washed away from the soil by rain. Denser clay-rich soils can retain micronutrients better, but they can also bind some of the nutrients with the minerals in the clay.
Soil pH is an important factor. If the soil pH is very alkaline, zinc and manganese are bound as hydroxides. On the other hand, a too acidic pH is harmful for plants, so pH adjustments of the soil must be done carefully.
If the soil is very wet and/or its temperature is very low, the micronutrients may change to a form that is less available for the plant because of their decreased solubility. Very wet conditions and oxygen-rich soil can also cause micronutrients to form insoluble minerals with each other, like zinc and iron do with oxygen, forming ZnFe2O4.
CHEMICAL BINDING TO THE SOIL
Carbonates are often used to adjust the pH, they lower the acidity of the soil. However, the pH should be monitored so that the increased pH and excessive carbonate ions will not bind the micronutrients into the soil.
Soils with a high organic matter content contain humic and fulvic acids which have a tendency to chelate micronutrients into their structure, leaving the micronutrients partially unavailable for the plant.
NPK fertilisers contain phosphorus, which dissolves into the soil. When the dissolved phosphorous is combined with dissolved micronutrients in alkaline conditions, they can form insoluble phosphates in the soil.
Some macronutrients like Ca and Mg can compete for space with micronutrients within the plant. This means that if excessive amounts of macronutrients are first absorbed by the plant, it cannot take in the added micronutrients as the plant structure is already saturated with nutrients.
BEST MICRONUTRIENT ABSORPTION RESULTS WITH FOLIAR FERTILISATION
Foliar fertilisation is often preferred for micronutrient fertilisation and is the single most efficient method of micronutrient fertilisation. However, tissue tests have shown that the most effective way of increasing nutrient content of zinc and manganese in plants is combined fertilisation through soil and foliar fertilisation.
When the micronutrients are sprayed onto the leaves, they absorb more efficiently into the plants, because there is no contact with the soil that could bind them. When ZM-Grow is sprayed on the leaves, the micronutrients go through the leaf structure in ion form. There they are utilized by the plant’s metabolism, providing the plant with the amount of micronutrients that it requires.
Best micronutrient absorption results with foliar fertilisation
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