Effect of cycle size on EC refreshment and EC stability

To avoid common fruit quality issues such as BER in tomato and pepper it is important to have EC under control in time and stable between days.

Using the GroSens look at how the EC develops over time, especially in relation to radiation, it should be stable from day to day. In this respect it is also very important to have EC refreshed in time during the day. Look critically to the recorded time of first drain on the computer and compare this to the time EC decreased in the slab indicated by the WCM, they should match. But in many circumstances drain will be recorded but EC will not be controlled (Figure 1). If left unchecked this can have devastating consequences for the crop.

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Figure 1

Unstable EC: Time of first drain recorded by the climate computer is about 09:30 hrs dark blue EC is not controlled until 12:00 hrs. The result EC rises over two days. If left unchecked this can result in serious quality issues such as BER. The issue, in this case, was that cycle length was reduced to early.

Figure 2 illustrates another example of how cycle length can affect the EC refreshment of the slab. Here the cycle length in too small resulting in drain too late

Figure 2

Unstable EC: Start time is OK, time of 1st drain and EC reduction this time in line but drain occurs too late because of small cycle length. The result EC is unstable and rising – here the reaction was to give a night session however the correct course of action would have been to increase cycle length. If left unchecked this could have resulted in aborted fruit.

The time of first drain is therefore very important in respect to EC refreshment. Within the irrigation strategy focus on the start time and the volume of irrigation that is given, to account for the decrease in WC and water uptake by the plant this can easily be 4,0-6,0 ml/J for the first 4-5 irrigation cycles (Figure 3), for more information see the 6 Phase email advice for your chosen slab type.

Figure 3

Drain and EC refreshment on time (10:00 hrs or 600W/m2)is achieved by applying large volumes in the morning 4,0-6,0 ml/J. Thereafter smaller more frequent irrigations in the relation 3,0-3,3ml/J keep EC controlled during the peak solar hrs and limit stress on the crop so that production and fruit quality is maximized.

Monitoring the EC in the slab

Monitoring EC in the slab is an essential part of weekly nutritional monitoring and should be undertaken on a daily basis. Sampling should take place in a number of representative slabs in order for a meaningful and accurate assessment to be made. Sampling is easy, simply push a syringe into the slab and extract a small quantity of nutrient solution (100 ml) and place this into the cup of the EC meter for a direct reading. Calculate the value for delta EC and plot this on a graph this will make it easier to identify trends. Alternatively the slab EC can be monitored directly over the course of the day and the results graphed automatically using GroSens. GroSens also measures and produces a graphical output of the slab water content and slab temperature. GroSens makes EC management easier.

Tips for accurate EC measuring using a portable meter

Calibrate the EC meter regularly using standard solutions.
Check the battery status, low batteries in portable EC meters are often a cause of error.
Always take measurements at the same time each day this will allow easier interpretation of the result.
Store the meter in a cool dry place.

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Learn more about EC management

By Anna Woronowicz

e-Gro

EC – important parameter for irrigation strategy

The electrical conductivity (EC) unit is commonly employed for analyzing fertilizer component concentrations in hydroponic growth’s nutrient solution or root zone. This involves measuring the electrical conductivity of a solution to determine the cumulative ions necessary for plants (e.g., NO3-, Fe3+) and ballast components (e.g., Na+). The EC value is usually expressed in either millisimens (mS/cm) or microsimens (µS/cm).