What are Nutrients?

There are many chemical elements, both in the soil and applied as fertilizer, but what are nutrients and what are not? The answer to this question is not quite as straightforward as you may expect, but it is important to understand, so you can use the right fertilizer and achieve the best growth. So what are nutrients in fertilizer and how do we use this information?

There are three aspects to this topic:

• The essential and non-essential nutrients
• The concept of plant availability and
• Nutrient balance

What are nutrients – essential or otherwise?

Plants can take up many elements, but only 16 are known to be essential for healthy growth:

Nutrients from the soil:

If any of these are in short supply, growth will suffer and nutrient deficiency symptoms may develop.

There are also a few other elements (such as Sodium and Silicon) that are non-essential in that they may be needed by some plants but not others, or they can play a nutritional role, but they tend to substitute for something else, so their absence causes no harm to growth. Of course there are also Toxic elements like Aluminium.

What are nutrients – available or not?

Nutrients in the soil can be present in a number of ‘forms’ including:

• Soluble
• Exchangeable
• Organic (as part of the dead organic matter)
• Biological (as part of living organisms)
• Mineral

While soluble nutrients are the easiest for plants to obtain, they may not be able to use Mineral forms at all, so the ‘availability’ of these various forms is different, with the Soluble and Exchangeable forms making up the bulk of what we call ‘available’. The aim of a soil test, then, is to discern only the amount of any nutrient present that is available for plants to take up through their roots and use.

Not only does the availability of nutrients vary between the different forms in the soil, but there are also nutrient cycles to consider.

What is nutrient balance?

Every plant variety has its own set of nutrient requirements and these will change somewhat through each of main growth stages – germination or bud burst, vegetative growth, flowering, fruit development, etc. Ensuring that the plant can access the right amount of each nutrient, as it is required throughout the season is the aim of balanced plant nutrition.

Of course this process is complicated a little by interactions between some nutrients.