What level of electrical conductivity should I have in my bedding crop?

What is EC and what is it measuring? 

• EC is the ability of a solution to conduct an electrical current.
• Water than contains salts like the ones in fertiliser can hold an electrical current.
• This current can be measured using a simple handheld EC meter.
• EC is usually measured in microseimens (µS/cm²) or millisiemens (mS/cm²).
• The more salts or fertiliser the water contains the higher the number will be from the EC reading.

Why is it important to know the level of EC?

Irrigation water from different sources will have different levels of EC.

The EC from one source will not be the same all the time, not even if it is mains water supply.

Taking regular measurements of EC can show where there is a decrease or increase of nutrient levels through a growing season.

Low levels of EC can be adjusted with increased feed to provide enough nutrition and avoid deficiencies.

Excessive EC levels of feed can be reduced to avoid nutrient toxicities, and damage to roots which can allow pathogens into the plant.

How often should EC readings be taken?

It is important to take readings every week, a constant mains water supply can change by 100 microsiemens (µS/cm²) from week to week.

If the water supply is switched because of low stored water to a blend with mains water, taking more regular readings is good practice as EC is likely to increase.

In recirculated water systems the EC of the recovered water will vary with the season and with weather events.

In lower temperatures EC is likely to be lower and stay lower. In warmer weather and during periods of rainfall the EC will vary a lot.

Testing the EC of recirculated water should be done to reflect the amount of variation that is likely to be seen.

Does everything need the same level of EC?

No, a high EC can damage young delicate roots, so a lower EC is better suited for germinating seeds and seedlings. Aim to add an additional 300-400 µS/cm² of a balanced feed.

As plants mature the EC should increase to provide the nutrients required for healthy growth. Aim for an additional 600-800  µS/cm² of a balanced feed.

Not all crops are the same, some crops such as Salvia are intolerant to high EC. It is important to add feed slowly, a little and often approach is better than large doses sporadically.

Will the EC tell me what nutrients are deficient in my irrigation?

No, an EC meter can measure total salts, but cannot measure the concentration of individual nutrients.

If you need to know the detail of what is in your irrigation water, you will need a laboratory analysis carried out.