Greenhouse Fertilizer Injector Calibration

In this video we will cover two methods
of how to calibrate your fertilizer injector. The first method is the E.C. method. This method uses a properly calibrated
electrical conductivity, or E.C. meter, a small amount of full strength
fertilizer, and a small amount of clear water from your tap. To get the full strength fertilizer
solution, start by filling a bucket with fertilizer solution from
the end of the hose. Be sure to allow at least one gallon
of full strength fertilizer to fill the bucket. Then using a small plastic cup, dip some
of the full strength fertilizer solution out of the large bucket. Use your E.C. meter to check
the E.C. of the full strength fertilizer solution. In this case, it is 1.74 millisiemens
per centimeter. Be sure to wash off the probe
with distilled water. We now need to refer to the label
of the fertilizer we are using. In this case, it is a 15-4-15. When we take a look closer at the
label, we see a table that gives directions for mixing, but also
the E.C. values for different concentrations of fertilizer. We have mixed our fertilizer and set our
injector to give us 200 parts per million nitrogen. So if we look at the last row on the
table labeled 200 parts per million and follow it over to the E.C. value
column, we see that we should get a value of 1.52 millimhos, or millisiemens
per centimeter. But we found the E.C. to be 1.74. We didn’t account for the
E.C. of the tap water. The E.C. of the tap water is found to
be 0.25 millisiemens per centimeter. Therefore, we subtract 0.25 from 1.74
to give us 1.49 millisiemens. This is pretty close to the 1.52
millisiemens that we’re looking for. In most cases, being within 200 to
300ths of a millisiemen is sufficient. Our second method is the flow method. At the core of the flow method
is this equation– diluted volume divided by stock
volume equals injector ratio. We start with filling a graduated
cylinder to a known volume with the concentrated stock solution. In this case, the cylinder
is filled with 200 milliliters of stock solution. Then we place the lead from the injector
into the graduated cylinder. Next, fill a bucket with fertilizer
solution from the end of the hose to a known volume. I’ve marked this bucket so I know
when I’ve filled it with 16 liters of water. The larger volume of water that
you will use will give you more accurate results. But in most cases, using between four
and five gallons of water works well. Once the bucket is filled to 16 liters,
the water is turned off. And the lead from the injector is
removed from the graduated cylinder. We now look at how much concentrate
is left in the graduated cylinder. There are 118 milliliters left, which
means to fill our bucket to 16 liters, we used 82 milliliters of concentrate. Now I need to use our calculator. The calculation has to be
done in milliliters. So we need to convert 16 liters into
milliliters by multiplying by 1,000 to get 16,000 milliliters, then divide
16,000 by 82, the number of milliliters of concentrate it took
to get 16 liters of solution. To show this again, we divided 16,000
by 82 to give us a little over 195. We anticipated our injector
to be set at 1 to 200. This tells us that it is actually
set at 1 to 195. For most cases, if we were within
1% to 2%, we are OK. And in this instance, we’re
within that range. If our injector’s off by too much using
either method, we will have to adjust the ratio. Injectors made by different
manufacturers will be adjusted differently. But with our injector shown here, we
simply twist this portion of the injector one way or the other to
adjust the ratio up or down. Thanks for watching this video on
calibrating your fertilizer injector. If you’d like written directions for
this, please visit our website at and look
under the Plant Nutrition tab.

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