Plant Tissue Test Instructions
From Pike Agri-Lab Supplies, Inc.

Introduction:

This method of plant sap analysis is relatively new. Sap is squeezed from the fresh plant tissue and analyzed for Brix, pH and EC. Data collected can be used as a tool in fertility management. Please note that the information contained here is preliminary.

Although research continues in the area of plant sap analysis, little interpretation data is available. Over a period of time, it is recommended that a grower establish his own data, based on analysis results, fertilizer applications and crop response.

Recommended tools:

* ATC-1e Refractometer
* Cardy Twin pH Tester
* Cardy Twin EC Tester
* Infra-Red Heat Gun
* Plant Juice Extractor (modified vise grips)
* Carrying Case & Instructions

OVERVIEW OF CROP MANAGEMENT
USING PLANT TISSUE TESTS

The following outline shows how you may be able to make improvements, based on the teachings of Carey Reams:

* At the end of a growing season, lightly incorporate that year’s organic matter into the top layers of the soil along with a complete nutrient and microbe package.
* Perform a soil test that evaluates the availability of major plant nutrients.
* Add nutrients in order to balance the major nutrients during fall or spring.
* Make sure that the soil contains proper levels of air, water, and organic matter, so that the microbes can build humus to satisfy the needs of the plants.
* Test the plant sap as soon as leaves are large enough to squeeze several drops of juice for testing. Perform the following tests to determine the needs of plants at any time during the season or at any growth-stage:

* Total dissolved solids (or Brix), measured with the ATC-1e Refractometer. This number indicates the level of balance of nutrient uptake and complexing into sugars or proteins in the photosynthesis factory – the leaf. If Brix is low, even after several hours of sunshine, some element(s) are missing in the photosynthesis factory. Ions, if present, have not been "complexed" into sugars or proteins.
* pH, measured with the Cardy pH Twin Meter, indicates elements, which may be out of balance. For pH<6.4, consider if there is a need for Ca, Mg, K, or Na. For pH>6.4, consider possible need for phosphates or sulfates. If the proper elements are selected and applied, the Brix reading will increase and the pH will go to the desired area of approximately 6.4.
* EC, measured with the Cardy Twin EC Meter, indicates the level of simple ion uptake into the plant sap. With low Brix crop, if sap EC is too low, elements are not being made available to the plant. Look at the EC of soil/water extract (or ERGS) and take appropriate steps to correct the condition. If sap EC is too high, elements or ions are not being "complexed" and ions such as nitrate nitrogen may be at excessive levels.

* In addition to the plant sap tests above, the following tests can be useful in monitoring the health of your crops:

* I.R. Stress, measured with an InfraRed Sensor. The more elevated the foliage temperature is above ambient air temperature, the more stress the plant is exhibiting. This is especially useful for identifying "hot spots" in your fields.
* Chlorophyll, measured with a chlorophyll meter. The chlorophyll reading can be especially useful in confirming suspicions of low nitrogen.
* Soil penetration resistance, measured with a penetrometer.

* Consider the test factors above when formulating foliar sprays to help create better and more balanced nutrient uptake into the plants. Every foliar spray should be a complete NPK and trace nutrient mix. By controlling the pH of the foliar spray, you can promote plant growth (foliage) early in the season, and then fruit (or root) production later in the season. The table that follows may be useful in putting together foliar sprays.


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Brix (>12) E.C. (2,000 – 12,000µS) pH
(6.4) Interpretation –
Remember: If things are not as they should be, look at factors such as compaction and/or weed growth to help determine what your soil is lacking.
High NA NA Good balanced microbial activity. Consider selling crop at a premium.
Low Low Low Ions are missing. May be due to a lack of microbial activity in the soil. Elements that act as carriers in the soil, such as nitrogen and phosphorus may be lacking. May also be lacking potassium or sodium. Look for soil compaction indicating that calcium to magnesium ratio is out of balance.
Low Low High Ions are missing. May be due to a lack of microbial activity in the soil. Elements that act as carriers in the soil, such as nitrogen or phosphorus may be lacking. May be lacking phosphates, sulfates, acetates, or humic acids.
Low High Low Ions are not complexed. May be due to a lack of microbial activity in the soil. Acid producing elements or ions are at excessive levels and not being "complexed". May be lacking calcium, magnesium, potassium, or sodium. High salt fertilizers may have been applied.
Low High High Ions are not complexed. May be due to a lack of microbial activity in the soil. Elements or ions such as nitrate nitrogen are at excessive levels and not being "complexed". May be lacking phosphate or sulfates or magnesium.

* Apply the foliar spray to a test plot. After a minimum of two hours of sunshine, test the Brix of the treated plants as well as some of the untreated plants. If the test area is at least 2 Brix higher than the control area, the spray was effective and can be applied to the whole field.

General Information

Please read the instructions included with each of the meters prior to calibrating, using, or storing them. Familiarize yourself with the do’s & don’ts involved in the handling for long term service, calibration, battery replacement, & other notes. Frequent calibration will increase confidence in the accuracy of the instruments.

It is very important that the testing surfaces of the plant sap testers (refractometer, pH, & EC meters) be thoroughly rinsed after each use. A final rinse in distilled water is suggested. Before testing samples, be sure to check the calibration of the meters, using standard solution(s). Follow the calibration instructions included with the meters.

Important Precautions

These instruments should not be dropped or handled roughly. Take extra care with the non-waterproof meters, but even the waterproof testers should not be completely immersed. Please check the information provided with each meter to determine whether it is waterproof, & also to familiarize yourself with any special care requirements. For example:

* Do not splash water on the body of the refractometer. Do not scratch the surface of the prism.
* Be very careful when cleaning the sensors of the Cardy testers. The thin glass membranes can be easily broken or scratched. Do not press on the sensors. Gently blot dry with a soft tissue.

PLANT SAP EXTRACTION

Sampling:

Select young leaves that are exposed to sunlight. Try to find leaves that represent the field area to be evaluated. Try to minimize the amount of stems and veins in the sample material.

Samples may be taken from several different plants, making sure that sufficient material is collected for chemical analysis. Leaves or parts of plants selected should be of the same age and relative position on the plants. You should establish sampling procedures for every plant type and then strictly adhere to those procedures.

Do not sample plants that show obvious signs of nutrient deficiency or damage from disease, insects, or chemicals unless this is the subject of the study. Plants that have been under stress for a period of time may not give a true picture of the nutrient status of the field.

Extraction & Testing Procedure:

1. Use a plant sap press (modified vise grips or hydraulic press system) to squeeze sap from the leaves. Place a portion of plant material in the press. For vise grips, leave a portion of a leaf extending beyond the jaws. (Allow the sap to follow the leaf so that it can be easily transferred.)
2. Transfer several drops onto each of the three sap testers: refractometer, pH tester, & EC meter.
3. Close the lid of the refractometer and take the reading. Record.
4. Switch on the pH meter and wait for reading to stabilize. Record.
5. Switch on the EC meter and wait for reading to stabilize. Record.
6. Carefully clean the instruments with distilled water.
7. Repeat the procedure for other samples if desired.

REFRACTOMETER

Refractometers are simple optical instruments for measuring the dissolved solids content of fruits, grasses, & vegetables during all stages of growth. The solids (sugars, proteins, amino acids, etc.) that are dissolved in the juice of plant tissues will bend light rays in proportion to: the quantity of all the atoms, the atomic weight of the elements, & the number of covalent bonds in the combinations of atoms such as sugars. Refractometers measure in weight % sucrose in water (Brix°) and can be calibrated with distilled water and/or sugar standard solution. Note: the ATC-1e automatically removes errors (up to 2 Brix°) due to changes in temperature (50-86°F).

The Brix indicates the level of balance of nutrient uptake and complexing into sugars or proteins in the photosynthesis factory – the leaf. If Brix is low, some element(s) are missing. Ions, if present, have not been "complexed" into sugars or proteins. If soil nutrients are in the best balance and are made available (by microbes) upon demand by plants, Brix will be higher.

Taking the Brix reading

Place 2 to 3 drops of liquid sample on the prism surface, close the cover & point toward any light source. Focus the eyepiece by turning the ring to the right or left. Locate the point on the graduated scale where the light & dark fields meet. Read the % sucrose (solids content) on the scale.

For reference, pure (distilled) water reads 0 °Brix.

Other Useful Brix Tests

Test the juice of fruits, vegetables, or grasses and compare them to the enclosed chart of Refractive Indexes (Brix readings). Within a given species of plant, the crop with the higher refractive index will have a higher sugar content, higher mineral content, higher protein content and a greater specific gravity or density. This adds up to a sweeter tasting, more minerally nutritious food (maximum nutritional value) with lower nitrate and water content and better storage attributes.

Crops with higher Brix will produce more alcohol from fermented sugars and be more resistant to insects, thus resulting in decreased insecticide usage. For insect resistance, maintain a Brix of 12 or higher in the juice of the leaves of most plants. Crops with a higher solids content will have a lower freezing point & therefore be less prone to frost damage.

E.C. METER

The Cardy Twin Cond meter measures electrical conductivity of plant sap, water, soil, compost, foliar sprays, etc. It has Auto Temperature Compensation (removes errors caused by temperature variance) and Auto-ranging (displays reading automatically in mS or µS, according to sample’s concentration).

EC indicates the level of simple ion uptake into the plant sap. With low Brix crop, if sap EC is too low, elements are not being made available to the plant. Look at the EC of soil/water extract (or ERGS) and take appropriate steps to correct the condition. If sap EC is too high, elements or ions are not being "complexed" and ions such as nitrate nitrogen may be at excessive levels.

Conductivity Cross Reference

1 milliSiemen (mS) is equal to 1000 microSiemen (µS). A mho is another name for a Siemen, so that a micro mho (µmho) is equal to a micro Siemen (µS). Conductivity is the reciprocal of resistivity (ohm).

Other Useful Conductivity Tests

Testing the conductivity (mobile ion concentration) of water or spray solutions:

Place several drops of the water or spray solution to be tested onto sensor of the calibrated EC meter (alternately, immerse the sensor end of the meter into the liquid, being careful not to immerse beyond the level indicated). Turn on the meter and wait for the reading to stabilize. Good quality spring or tap water should be < 100 µS; distilled water should be < 10 µS.

Testing soil "ERGS" or conductivity of soil/water mixture:

ERGS (as defined by Reams, is Energy Released per Gram of Soil). A desired level would be 100-200 µS.

1. Use a small beaker or cup to measure out a fixed volume of soil. Do not pack soil into cup, but fill any voids of > 1/4" diameter. Fill cup to brim & remove excess with a clean straight edge.
2. Pour into a larger jar or cup with a lid.
3. Measure an equal volume of low conductivity (i.e., less than 5µS) distilled water. Pour into jar or cup.
4. Cover the jar. Gently shake contents back and forth 5 - 7 times to partially put into solution the ions that are loosely bonded to soil particles or humus molecules. Allow soil to settle to bottom of cup. The goal is to extract those ions that would be most readily available to the plant rootlets.
5. Place a few drops of the filtrate onto the sensor of the calibrated EC meter (alternately, immerse the sensor end of the meter into the liquid, being careful not to immerse beyond the level indicated). Turn on the meter and wait for the reading to stabilize.
6. Rinse the sensor with flowing stream of tap water. Spray rinse with distilled water. Several rinses may be required in order to obtain reading of < 1 µS with good distilled water.

Plants grow from the interaction of simple ions. During the major growth phase of the plant, ERGS should not be <100 µS. Values of 200 – 400 µS are very good when ions derived are from good balanced plant nutrients. The ERGS should not be allowed to go to a level of < 100 µS during the growth phase of a plant, if a reasonable yield is expected. If soil ERGS is > 1200 µS, most plants won’t survive. Corn will do well at higher ERGS levels during plant production phase.

Low ERGS, (50 µS or less), indicate that soil nutrients have become insoluble or complexed. This means they are not readily available to the plant and results in poor growth potential.

Establish baseline conductivity levels in early spring before rising temperatures activate soil life. Salt residues and latent plant nutrients in soil should form a baseline of 25-600 µS.

High conductivity in soils is an indication of possible nematode susceptibility.

Testing electrical conductivity (E.C.) of compost:

1. Gather a fresh compost sample in a plastic bag, taking care not to touch sample with hands.
2. For compost, a 50% by weight moisture level is desired for the sample prior to testing.
3. Follow steps outlined for soil ERGS testing (above).

Compost in early stages may have an EC of <10,000 µS. At the peak of the breakdown stage, it may have an EC of >100,000 µS. Highest quality, water-stable, nutrient-rich (unleached) finished compost should be approximately 1,500 µS.

PH METER

The Cardy Twin pH meter tests hydrogen ion activity. This meter has Automatic Temperature Compensation (ATC) which removes errors caused by temperature variance. The acid/alkalinity reading determines balance of soil microbes and can be used to make decisions on balancing soil additives. Foliage (plant tissue) pH is indicative of nutrient uptake and potential of pressure from insects and disease.

pH indicates elements, which may be out of balance. For pH<6.4, consider if there is a need for Ca, Mg, K, or Na. For pH>6.4, consider possible need for phosphates or sulfates. If the proper elements are selected and applied, the Brix will increase and pH will go to the desired area of ~ 6.4.

Other Useful pH Tests

Testing the pH (Hydrogen ion activity) of water or spray solutions:

Place several drops of the water or spray solution to be tested onto sensor of the calibrated pH meter (alternately, immerse the sensor end of the meter into the liquid, being careful not to immerse beyond the level indicated). Turn on the meter and wait for the reading to stabilize.

Testing pH of soil/water mixture:

1. Use a small beaker or cup to measure out a fixed volume of soil. Do not pack soil into cup, but fill any voids of > 1/4" diameter. Fill cup to brim & remove excess with a clean straight edge.
2. Pour into a larger jar or cup with a lid.
3. Measure an equal volume of distilled water. Pour into jar or cup.
4. Cover the jar. Gently shake contents back and forth 5 - 7 times to partially put into solution the ions that are loosely bonded to soil particles or humus molecules. Allow soil to settle to bottom of cup. The goal is to extract those ions that would be most readily available to the plant rootlets.
5. Place a few drops of the filtrate onto the sensor of the calibrated pH meter (alternately, immerse the sensor end of the meter into the liquid, being careful not to immerse beyond the level indicated). Turn on the meter and wait for the pH reading to stabilize.
6. Rinse sensor with flowing stream of tap water. Rinse with distilled water. Several rinses may be needed.

Soil pH of 6.5 is generally ideal. Plant nutrient availability is dependent on soil pH.

Testing pH of compost:

1. Gather a fresh compost sample in a plastic bag, taking care not to touch sample with hands.
2. For compost, a 50% by weight moisture level is desired for the sample prior to testing.
3. Follow steps outlined for testing pH of soil/water mixture (above).

The pH should be between 7.0 & 8.0.

Measure the microbial activity level of Soil or Compost:

1. Add 1/4 ml of Soil Stripper Solution (available from Pike Agri-Lab Supplies) for every 10ml of original water volume to the sample mixture (for example, use 1.5 ml of Soil Stripper Solution for 60ml of water), replace the cap and mix for 30 seconds. Let settle for 1 minute.
2. Use the pH meter and read the new pH value. Record this value as "KCL pH". Note the magnitude of decrease (or increase, under some conditions) in pH from initial reading and this number is referred to as "pH differential" or "? pH".

The "pH differential" decrease from the "actual pH" (with water) should be no more than 0.5 for soil and 0.3 pH units for compost. This change is caused by the KCL in the Soil Stripper Solution knocking hydrogen ions off the clay colloids. A small drop in pH indicates a good buffering capacity, which is a sign of biological life.

Observations about pH

1. Certain nitrogen-fixing microbes won't live if pH is < 5.8
2. Pesticide usage may be reduced if water mixture pH is < 6.8
3. Herbicide usage can be reduced by correcting spray pH
4. Soil pH profiles can be indicative of soil compaction
5. Early growth plants will respond to alkaline sprays, i.e. pH 7. - 7.4. Later in the season, fruit, root, or seed producing foliars require acid pH (6.4 or lower).
6. Rainwater in equilibrium with carbon dioxide will have a pH of 5.6. Acid rain has been recorded as low as pH of 3.0
7. Drying a soil at a temperature above field conditions will increase soil acidity. During later part of season, organic acids produced by microbes will be at a higher concentration.

To raise soil pH: Use the following alkaline substances diluted in water: KOH, Ca(OH)2, Baking soda, NH4OH, CaCO3.To lower soil pH: Use the following acidifying substances diluted in water: vinegar (acetic acid), citric acid, ascorbic acid, phosphoric acid, sulfuric acid.

INFRA-RED SENSOR GUN

Note: The USDA has researched the stress level in plants as a function of temperature rise above ambient air temperature. The IR gun provides a simple, fast and accurate means of testing the differential temperature (D T).

Conditions required for testing:

1. Plant leaf surface must be dry.
2. Use only when wind is blowing at less than 10 mph.
3. Keep the sunlight at your back.
4. Use a sheet of plain white paper for determining ambient air temperature.
5. Take I.R. readings from foliage only during the peak sunlit hours of the day, when stress is most likely to occur. Therefore, take readings from 11 AM to 4 PM during the summer and from 1 PM to 3 PM during the winter.
6. If air temperature is much cooler than normal, then I.R. plant stress will not be measurable with this instrument.
7. You must have at least 2 minutes of sunlight immediately following an interruption by clouds.

Directions for taking differential temperature readings between ambient air and plant leaf surfaces:

Note: The sensor has 8 to 1 optics. This means that the beam diameter is 1/8th of the distance from the sensor to the object at the center of the beam. The beam will be oval, (similar to a flashlight beam) when you shine the gun at an angle to the foliage.

1. Determine ambient air temperature. Point gun at center of 8.5" wide sheet of white paper. If you hold the sheet 24" from the IR gun, then the 3" diameter region will be providing the ambient temperature reading.
2. Hold the sensor so that the beam will not see the sky or dirt.
3. Take readings while in the field, not while in a pickup truck.
4. View only the vegetation.

5. Notes on Corn: After the 5th leaf stage, aim at individual plants or down the rows. Once there is a full canopy, readings may be made from an elevated platform. For readout of foliage temperature, take multiple samples, average the readings. Generally, the larger the area, the more samples you should take.
6. Record the differential temperature between ambient air and average foliage temperature. The magnitude of this temperature difference is a measure of the stress level of the plants.

Factors affecting readings:

1. Tree crops will transpire water slowly.
2. Row crops transpire a greater amount.
3. Overcast skies, clouds, and cold fronts cause I.R. plant stress to decrease.
4. Early in the season, with small leaf area and shallow roots, stress will rise rapidly. Later in the season, large leaves and deeper roots will stabilize the stress factor.
5. Stress may increase immediately after irrigation or soaking rain, especially in heavy soils. The lack of oxygen to the roots inhibits the ability of the plant to absorb water from the soil.

I.R. Stress Reading related to crops:

1. In general, a differential temperature of +1or 2 degrees Celsius is very good. If the foliage is 10 ° C warmer than ambient air, the plant is seriously stressed and cause of problem needs to be determined.
2. Overall, the cooler a particular crop stays, the higher the yield and the better the quality of the crop.
3. In order to produce maximum yield on seeds, the plant stress should follow a sawtooth pattern over the course of the growing season. Start the season with low stress to promote plant growth. Then create stress in order to stimulate seed production. Thereafter, maintain the vigor of the crop in order to complete the production of seeds.

General notes:

Leaf Temperature varies directly with:

Ambient air temperature

Sunlight level

Relative humidity

Leaf Temperature varies indirectly with:

Water

Oxygen

Plant stomata will open if potassium is high.

Plants evaporate water if stomata are open.

As drying power increases, plant temperature goes down (evaporative cooling).

If air is saturated with moisture, i.e., relative humidity is high, leaves will evaporate less.

Late in season, as leaves dry, stress index will gradually increase to moderate levels.

A leaf with closed stomata will be hotter.

Stomata will close if:

Water levels are low

Disease or insects are present

Response may be slow due to:

Slow water penetration into soil

Delay of re-growth of new roots

Call us to see how we can help you grow better:

Pike Agri-Lab Supplies, Inc.

RR 2 Box 710

Strong, Maine 04983

Phone (207) 684-5131 · Fax -5133

e-mail: info@pikeagri.com




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