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Using the PourThru Technique to Monitor Nutrition by Paul Pilon

May 25, 2010

Maintaining proper nutrient levels is essential to producing healthy and high quality crops. It is recommended for growers to conduct media testing using in-house methods on a weekly basis and to periodically send samples to a commercial or university laboratory for nutritional analysis.

The two most important and practical measurements that growers can collect at their facilities are the pH and EC (electrical conductivity or soluble salts) of the growing medium. The pH of the growing medium determines how available certain nutrients are (particularly the micronutrients) and the soluble salts reading (EC value) measures the total soluble salts in a solution (not the individual nutrients).

PourThru Extraction Method

The PourThru extraction method has become one of the most popular methods growers use to monitor the fertility levels of their crops. This in-house testing procedure is a quick and simple method growers can use to determine the pH and ECs of their crops. Each individual test provides an image of the nutritional status (nutrients available) of the crop at that given time. A series of tests provides an indication of where the crop has been and where it is likely to go (trend) if the current practices are kept in place.

There are several advantages of using the PourThru method over other testing procedures. The results obtained closely resemble the actual soil solution that plant roots are growing in, providing a clearer picture of the availability of plant nutrients. The PourThru method requires less time to conduct, and does not require sophisticated equipment to provide accurate results. It is a nondestructive testing procedure that does not disturb the root systems of healthy plant materials. PourThru extracts can still be sent to laboratories for thorough nutrient analysis. 

As with all testing procedures, it is important to standardize the testing procedures so they are conducted the same way every time. The PourThru method of nutrient extraction involves pouring distilled water onto the surface of the media and collecting the extract, often called leachate, from the bottom of the container. The leachate collected results from the displacement of soil solution by the distilled water poured onto the media surface. 

Using water sources besides distilled water to conduct PourThru testing is acceptable. The pH of the leachate collected may be altered slightly, especially if the alkalinity of the alternative water applied is over 150 ppm. If your water source has an alkalinity of over 150 ppm, it is best to use distilled water to conduct this test. 

It is important to water the pots to be tested thoroughly, using the same water source, or fertilizer solution, that is normally applied, one to two hours before conducting this test. Failure to water the pots thoroughly before testing causes an improper displacement of the existing media solution. If this occurs, it is possible for the leachate collected to closely resemble the EC and pH of the water you poured on the pots, instead of the pH and EC of the growing medium being tested.

Conduct PourThru tests on at least 5 pots from any crop. Each pot should be tested individually, but the results of the 5 pots should be averaged (not mixed together) to determine the nutritional status of the crop, and if any fertility adjustments must be made. The sample pots should originate from the center of the block, samples taken from the outside rows are usually not reflective of the true nutritional status of the crop, as they dry out faster, and may have been irrigated differently. To obtain the most representative results, pick sample plants randomly, do not select the best or the worst looking plants. 

Regardless of the size of the pot being produced, apply enough water to the top of the growing medium to collect 2.0 ounces of leachate. Note only the first two ounces of leachate should be collected, collecting more than 2.0 ounces will result in diluted results. It is best to apply the least amount of water to the top of the pot as possible to collect the 2.0 ounce sample. The pH and EC are measured from the solution collected.

EC Sufficiency Ranges and Comparative Values 

PourThru
Extraction Method

2 Water : 1 Media
Extraction Method

Saturated Media
Extract (SME)

Indication

0 to 1.0

0 to 0.25

0 to 0.8

Very Low

1.0 to 2.5

0.25 to 0.75

0.8 to 2.0

Low

2.5 to 4.6

0.75 to 1.25

2.0 to 3.5

Normal

4.6 to 6.5

1.25 to 1.75

3.5 to 5.0

High

6.5 to 7.8

1.75 to 2.25

5.0 to 6.0

Very High

>7.8

> 2.25

> 6

Extreme

Target ranges (Normal) are simply where plant growth can be maximized, ideally nutrition should be maintained between the maximum and minimum target ranges. When the test results rise above or fall below the targeted (acceptable) levels, a change in the current practices should occur to bring the nutritional levels back to the desired levels. If these adjustments are not made then undesirable results such as nutrient deficiencies or injury to the roots from excessive salt levels are likely to occur. 

Nutritional monitoring using the PourThru method helps growers to track nutrition, diagnose nutritional shortfalls or overages, and to correct any minor problems before they develop into big ones, which could lead to potential crop losses or unsalable product. Routine testing allows growers to make informed decisions regarding crop fertility over time.

Paul Pilon
Perennial Solutions Consulting
paul@perennial-solutions.com

 

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