Express Testing of Substrate pH and EC: Essential Tips for Efficient Monitoring

Understanding the Virginia Tech Extraction Method: A Legacy in EC and pH Testing for Substrate Culture

What if I told you that there is a non-destructive method that rapidly tests the EC and pH of the substrate medium in under 5 minutes without specialized tools?

Fortunately, we got the Virginia Tech Extraction Method or the Pour Through Extraction Method.

For over 40 years, The Pour-Through method has proven itself as a robust yet simple method for testing substrate chemical properties (Yeager et al., 1983).

The Art of Balancing EC and pH: Keys to Optimal Plant Nutrient Management

Monitoring container media EC and pH could be a useful tool for two reasons. First, by measuring EC we identify if plants have enough mineral nutrition. For example, leachate pH drops when Ca and Mg levels are low. Conversely, leachate pH tends to increase with higher Ca levels (Altland, 2021). Second, when measuring pH we determine if the plants can easily access mineral nutrients present in the media. Refer to Optimal pH in Hydroponics to learn more about pH in hydroponics.

Step-by-Step Guide: Performing the Pour-Through Extraction

To measure container pH and EC properties with the Pour-Through method, substrate solution should be extracted from the container medium.

To perform the Pour-Through extraction you would need the following:

• Calibrated Electrical conductivity (EC) meter

• Calibrated pH pen or meter

• Tray or saucer for leachate collection

• Small tall vial that holds 50ml (1.7 oz.) of leachate

• Coffee filter or paper towel to filtrate leachate before measuring (optional)

Key Considerations for Accurate pH and EC Readings

To ensure more accurate pH and EC readings, substrate saturation, water source, timing of application and leachate volume should be considered as part of your substrate extraction procedure.

Water Quality in Testing

The main function of poured water is to push the nutrient solution present in the substrate for collection without mixing or adding minerals to leachate extract. Hence, distilled or deionized water is commonly used. However, Studies by Yao and collaborators (2008) reported no effect on pH and EC of Pour-Through leachates when using water with EC in the range from 0.001 to 0.93 dS/m. It's also useful to consider the aspects of water quality, as outlined in Irrigation Water Quality Matters, for better insights into substrate testing.

Recognizing Substrate Saturation: Key Indicators for Accurate Testing

Before the Pour-Through method procedure, the substrate should be saturated with irrigation water to ensure consistent moisture content in the substrate, a crucial part of container substrate chemical properties monitoring. It is important to ensure that the moisture level of the container medium is at or near the maximum water-holding capacity. Once the substrate solution's chemical properties are stabilized and physical movement through the container pore spaces is complete the substrate solution reaches equilibrium. A simple indicator of the substrate reaching water-holding capacity is the glistering of the substrate surface. Another indicator is drainage. Wait until drainage is complete (30-60 minutes), but do not wait too long, since evapotranspiration 120-240 minutes following the irrigation event may result in reduced leachate extract volumes. Any volume of displacement solution applied to the container surface should displace the same volume of substrate solution from the bottom of the container if the substrate medium is fully saturated.

Timing Your Nutrient Solution Extraction: Best Practices for Accurate Results

Timing of extraction could affect the volume of collected leachate, pH and EC readings. In studies by Cavins et al. (2005) and Cavins et al. (2008) application of displacement solution 120 minutes after irrigation did not affect pH and EC readings but resulted in a collection of a reduced volume of leachate. Studies by Compton and Nelson (1997) did not see an effect on pH and EC 60 minutes and 120 minutes following leachate collection. Later studies by Yao et al. (2008) did not observe pH and EC changes of collected leachate between 20 and 120 minutes following irrigation. Therefore, displacement of leachate solution could be performed between 60 to 120 minutes following the irrigation event to ensure consistent pH, EC and collection of adequate substrate solution volume for analysis, as part of your pH and EC monitoring strategy.

The Right Amount: How Much Leachate is Needed for Accurate Analysis?

The goal is to collect at least 50 ml of leachate for testing. Excessive application of distilled or deionized water may dilute the substrate solution. For best results refer to Table 1 adapted from Dr. Neil Mattson from Horticulture Department at Cornell University. This step is vital in the substrate nutrient solution extraction process.

A Straightforward Method for Nutrient Solution Extraction: Key Steps

The process of nutrient solution extraction is simple:

1. After pouring the deionized or distilled water wait for approximately 5 minutes for the leachate to drain into the collection vessel.

2. Then, filter the collected solution through a paper towel or coffee filter.

3. Congratulations, you are now ready for pH and EC analysis!

Collect the leachate from more plants for a better understanding of EC and pH uniformity.

Insight into Pour Through Extract: Adjusting EC Readings for Accuracy

We should always remember that Pour-Through extract is undiluted and EC values are typically 1.5 times higher than values obtained with Saturated Medium Extract (SME) used in commercial laboratories. To convert from Pour Through to SME method simply multiply EC reading by 0.75 (Evans, 2014).

Measuring EC and pH in container substrate leachates provides an effective way to understand the combined effects of nutrients, irrigation water quality, and irrigation efficiency on plant growth. For a comprehensive approach to optimizing these measurements, the article Optimizing EC and pH in Substrate: Essential Strategies offers valuable insights and techniques.

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Express Testing of Substrate pH and EC: Essential Tips for Efficient Monitoring

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