Substrate pH

Substrate pH

substrate pH

pH determines micronutrient solubility in the root substrate:

•             low pH = very soluble

•             high pH = less soluble    


Plant takes up soluble nutrients through roots                   

►           Nutrients transported into leaves and growing points:

•             Excess = toxicity

•             Adequate = healthy

•             Insufficient = deficiency

►           Toxicity or Deficiency results in stunted growth, poor plant appearance, and un-saleable plants


. Why is pH important?

The most common nutritional problems occur in greenhouse container-grown crops when pH of the root substrate (also called potting mix or growing substrate) is outside the acceptable range. Substrate- pH measures acidity (low pH = acid) or basicity (high pH = basic, also called alkaline) of a root substrate, which affects a chain of events that ultimately affects plant health.

Plants take up dissolved nutrients through their roots. Substrate-pH drives chemical reactions that determine whether nutrients are either available for root uptake (i.e. soluble and dissolved) or unavailable for uptake (i.e. insoluble and solid). The most important nutrient affected by substrate- pH is iron (Figure 1). Iron, phosphorus and the micronutrients manganese, copper, zinc, and boron also decrease in solubility at high pH. Molybdenum increases in solubility at high pH.

The acceptable range for most crops growing in a soilless substrate is 5.6 to 6.4, because in this range micronutrients are soluble enough to satisfy plant needs without becoming toxic.

Recognizing the problem

Iron is required by plants to produce chlorophyll (the pigment in leaves which gives plants their green color). At high substrate-pH, iron (as well as most other micronutrients) becomes less soluble in the root substrate, resulting in lower uptake by the plant

(Figure 1). Because iron is not mobile within the plant, deficiencies induced by high pH tend to show chlorosis (yellowing caused by lack of chlorophyll) in the growing

tip. Sometimes, the chlorosis is over the entire leaf, but it can also be interveinal (leaf veins are green, but remaining tissue is yellow) as shown with the picture above of petunias grown at high pH. As the deficiency becomes more severe, plants lose vigor and the color of the chlorosis changes from yellow to almost completely white with necrotic (dead) areas forming at the growing points.

At low substrate-pH,

iron and manganese are highly soluble in the root substrate. Excess micronutrients can accumulate in plant tissue and cause chlorosis and necrosis (dead tissue) on leaf margins and as leaf spots, as shown in these geranium and marigold leaves. The damage tends to occur in older leaves because the longer a leaf grows on the plant, the more time it has to accumulate excess micronutrients.

Why do Substrate-pH problems arise?

Reasons that substrate-pH can be too high or low include:

3A. Poor buffering of soilless substrate. The move away from use of soil in greenhouse container substrate has many benefits (uniformity, consistency, aeration, sterility) but results in less buffering (chemical resistance to pH change) than soil.

A pH unit change within one week can sometimes occur with soilless substrate. Substrate-pH can drift up or down depending on the balance of factors including water alkalinity, lime activity, acidification of the substrate by plant roots, and use of an acid or basic reaction fertilizer. As a result, it is important not just to blame problems on the substrate or

fertilizer, but rather to also understand how grower management can cause pH to change over time.

3B. Limestone. Limestone is mixed into substrate to raise pH to around 6.0 because both peat and bark are acidic. Limestone sources differ in their composition, particle size, and hardness, which causes them to vary in their reactivity (i.e. how many pounds per cubic yard are required to raise pH at the start of the crop), and also in how long they continue to react during crop growth.

If the incorrect type or quantity of lime is used during mixing of the substrate, pH can either be out of range at the start of the crop, or it can drift over time. If mixing your own substrate, (a) consult a fertilizer or substrate company to obtain a suitable type of lime, (b) run small batch tests to check how much lime is needed to bring pH up to the target level, and (c) if you change the source of lime, peat, bark, or vermiculite you will need to re-test your recipe.

If you consistently run into problems with high or low substrate-pH, and you have correctly matched the fertilizer type with water alkalinity, consider changing the lime type or rate.

3C. Wide range in crops. Species differ in their nutritional needs, and can be separated into three nutritional groups based on their efficiency at taking up iron from the root substrate.

  • Petunia group: Also known   as                                             iron- inefficient      species, prone     to                                                               iron deficiency                    at                                 high substrate-pH, especially                                               when combined with low fertilizer concentration.                Grow at a lower substrate-

pH range of 5.4-6.2 to maximize iron solubility. This group is often misdiagnosed as a “high feed” or “high iron” group. They do not necessarily require higher

rates of fertilizer or iron, but are especially sensitive to high pH and the need for adequate iron. Examples include bacopa, basil, blueberry, calibrachoa, diascia, nemesia, pansy, petunia, snapdragon, vinca.

  • General group: Not prone to pH related problems. Grow at a moderate pH range of 5.8-6.4. Examples include chrysanthemum, impatiens, ivy geranium, poinsettia, tomato.
  • Geranium group: Also known as iron-efficient species, prone to iron/ manganese toxicity at low pH, especially when combined with high fertilizer concentration. Grow at a higher substrate-pH range of 6.0-6.6 to limit the

solubility of iron and manganese. Examples include marigold, seed and zonal geranium, New Guinea impatiens, and lisianthus.

Figure 1. The effect of growing petunia at different substrate-pH levels on

(A) soluble iron content in the soil solution, (B) iron content in the leaf tissue, and (C) leaf chlorophyll content. As pH increased there was decreased iron uptake. At the highest pH, substrate and tissue iron levels were the lowest, and the plants showed classic iron deficiency symptoms (chlorosis due to the lack of chlorophyll, see photo above right on this page). Research by Brandon Smith and Paul Fisher, Univ. of New Hampshire, and William Argo, Blackmore Co.

petunia pH effects
iron deficiency leaves

. Fertilizer type.

You cannot measure

the acid or basic reaction of a water-soluble fertilizer by measuring the pH of the stock tank or the solution coming out of the end of the hose. Rather, it is the tendency of a water-soluble fertilizer to change substrate-pH over time after the fertilizer interacts with plants or microbes.

The label on a fertilizer bag usually provides information on the acid or basic reaction of a water- soluble fertilizer expressed as an acidic or basic “calcium carbonate equivalency” (CCE). The CCE is a relative measure of the tendency of the fertilizer to raise or low lower substrate-pH (Table 1).

More importantly, the label tells the type and percentage of the different forms of nitrogen

(ammonium, nitrate, or urea), as well as the percentage of the other nutrients contained in the fertilizer.

In general, ammoniacal and urea nitrogen are acidic, and tend to drive the substrate-pH down, whereas nitrate nitrogen is weakly basic and tends to drive the substrate-pH up.

Several factors are important when using fertilizers to raise or lower substrate-pH:

  • Nitrate only increases substrate-pH when the fertilizer is taken up by plant roots. Therefore, if plants are small, or are stressed and not growing, nitrate has little influence on substrate-pH.
    • Ammonium can cause the substrate-pH to go down even if the plant is small or is not growing, because soil bacteria acidify the substrate through a process termed nitrification.
    • Ammonium is less effective at lowering substrate-pH in cool, saturated soil because nitrification is inhibited. In addition, ammonium toxicity in plants can occur in cool, wet conditions because plants are more likely to take up excess ammonium.
    • Sometimes ammonium will not drop substrate-pH at all because other factors (especially excessive lime rates in the substrate or high water alkalinity) can have a stronger effect on pH than the fertilizer, counteracting the pH effects of the fertilizer.

Table 1. Calcium carbonate equivalency (CCE), and the percent of acidic nitrogen1 contained in several commercially available water-soluble fertilizers. 1% acidic nitrogen is calculated as the sum of ammoniacal and urea nitrogen divided by the total nitrogen contained in the formula 2Units for CCE are pounds acidity or basicity per ton of fertilizer.

table calcium carbonate in substrate pH treatment

Irrigation water alkalinity.

Irrigation water pH affects chemical solubility of solutions, but has little effect on substrate-pH.

Instead, substrate-pH is affected by water alkalinity, which is a measure of the basic ions, mainly bicarbonates and carbonates, dissolved in the water. Alkalinity can be thought of as the “liming content” of the water, and irrigating with a high alkalinity water (above 150 ppm CaCO3 of alkalinity) can cause substrate-pH to increase over time.

Options for alkalinity management are:

Alkalinity can be reduced by injecting strong mineral acids (like sulfuric or phosphoric acid) into the irrigation water.

It may be feasible to change or blend water sources. Rain water collected in cisterns or ponds and water purified using reverse- osmosis contain little if any alkalinity.

Matching the alkalinity of the water to the reaction produced by the fertilizer is the most important decision growers can make to maintain a stable pH. For example, a low- alkalinity water should be balanced with a “basic fertilizer” (Table 1, containing low levels of ammoniacal nitrogen). A high- alkalinity water can be balanced with an “acidic fertilizer” (one high in ammoniacal nitrogen). Problems can occur when using ammonium-based fertilizers in cold weather (see 3D above).

1.   Substrate-pH and electroconductivity (EC) are the most important soil measurements. This article also mentions pH and EC test options for hydroponics.

If you can maintain substrate-pH and substrate-EC within acceptable limits and select an appropriate growing substrate and fertilizer, you will avoid 95% of nutritional problems.

  • Substrate-pH affects how soluble fertilizer nutrients will be in the growing substrate, especially micronutrients such as iron, and soluble nutrients are the only ones available for uptake by roots.
  • Substrate-EC measures how much nutrients are in the growing substrate. Substrate-EC is also increased by non-fertilizer ions such as sodium and chloride (table salt) that do not help plant growth.

You could send samples into a lab for pH and EC testing, but unless you have a very small greenhouse it is better to purchase a pH and EC meter and use the laboratory for more detailed analysis of water quality and specific nutrient levels.

The advantages of in-house testing of pH and EC are the low cost and the ability to quickly take a lot of samples on a regular basis.

The goal is to keep the pH and nutritional levels within an acceptable range and to spot problem trends early on. This is a far better strategy than

having to take dramatic steps to rescue stressed crops.

You can therefore use substrate-pH and substrate- EC results to make fertilizer decisions in a simple, systematic way. If pH is too low (acidic), then basic fertilizers are needed. If the pH is too high (basic), then acidic fertilizers can be applied. If the EC is too low (deficient in nutrients) then fertilizer concentration can be increased. If the EC is too high, then apply less fertilizer and perhaps remove fertilizer from the pot by leaching.

[H EC Testing of Substrates

In general, there is no one “best” method for measuring substrate-pH or EC in the greenhouse. Consider how much experience you have with a particular method as well as how much help and advice you can get from other people that are close by such as other growers, extension agents, universities, or soil testing laboratories. The chart above, and descriptions of each method may also help you in choosing between methods.

In container substrates:

  1. Pour-through: Distilled water is poured into the top of the pot displacing a small amount of the soil solution. The solution is then collected at the base of the pot. This method is good for rapid, non- destructive measurement in the greenhouse, and is especially good for large pots or pots that contain slow-release fertilizer prills which can break open and give false readings with the 1:2 or Saturated Paste.
  • 1 part soil:2 parts water dilution (“1:2”): Soil is removed from the pot, mixed with twice the volume of water, and pH and EC of this solution are

measured. This method is good for running many samples, and guidelines are well established. In Europe and some other countries, a similar method is used but with more or less water meaning that the EC guidelines differ because of dilution.

  • Saturated Paste Extract (“SPE”): A small sample of soil is removed from the pot and enough water is added to the soil sample to saturate air spaces. This is generally the most consistent method but also takes slightly more time to prepare. This method is used by commercial labs, and is also known as the saturated media extract (SME) method.
  • Plug squeeze method: An hour after irrigation, or when a plug is still close to saturation from misting, the soil solution is squeezed out of the plug and collected. This method is used for plugs where samples are difficult to handle with the above methods.
  • Direct measurement: Sensors with fine tips are placed directly into the substrate. This method is used mainly with plugs or saturated hydroponic substrates such as rockwool or coconut coir, using sensors that can measure directly into the growing substrate. This method is faster but more variable (especially for pH) than other methods.

In hydroponic culture:

  • Drip and drain: When growing in enclosed bags or a highly porous substrate such as volcanic rock, test the pH, EC and volumes of both the applied (drip) solution and the leachate (drain) solution and compare trends over time. Many growers have a target leaching fraction (drain volume/drip volume) that is measured and maintained to manage EC level.

pH and EC targets for the drip solution related to the input from the fertilizer injector (typically EC 1 to 2.5 mS/cm depending on crop and pH 5.8 to 6.2). Acceptable pH target for the drain is typically around 6.0 and is managed with acid or base injection of the drip solution. A crop-specific upper EC limit is defined (typically

between 2.5 and 3.5 mS/cm) and is managed using both the drip EC and leaching fraction.

  • Reservoir: In liquid hydroponic culture such as nutrient film technique (NFT) or deep water culture there is very little substrate. Therefore, the reservoir itself is sampled, often with continuous inline monitoring.

The pH is adjusted using acid or base injection and a low EC is corrected by adding stock solution. When EC is excessively high, a portion of the nutrient solution is usually discharged and the reservoir is diluted from fresh water. Typical pH target is 5.8 to 6.2 for all crops, and EC 1.5 to 2.5 mS/cm depending on the crop.

Consistency is the key

In order to make decisions, you need good data. This means purchasing a good quality pH and EC meter and calibrating the meter before each use (see our article on this topic). Consistency starts with having a single, trained person performing the test. Choose one method and stick with it. Follow the detailed sampling steps described in our other articles.

Interpreting your results

After you measure the sample, use the correct standards to check whether pH and EC are in the optimum range.

Each method can give different results, especially for EC, because methods vary in how much the soil solution is diluted. For example, diluting a sample by half with distilled water will result in half the EC level. pH is less sensitive to the testing method, but can still vary by ±0.5 pH units between testing methods. This means that you need to use the correct tables to interpret results and be consistent.

For example, less water is added in the SME method than with the 1:2 (i.e. the 1:2 results in a

more dilute solution). EC levels are therefore lower from a 1:2 soil test compared with an SME soil test.

The optimum substrate-pH (Table 1) varies depending on the tendency of a crop species to have problems at low pH (micronutrient toxicity, for example marigold) or at high pH (micronutrient deficiency, for example petunia). The optimum pH is designed to make nutrients soluble enough for healthy uptake without the risk of excess and toxicity.

Substrate-EC is a measure of the total salt concentration in the extracted solution. The EC measurement does not indicate the concentration of any individual plant nutrient. The only way to determine exactly what ions make up the EC is to use a more detailed commercial laboratory analysis. Caution is needed in interpreting an “optimum EC” when deciding whether plants have received sufficient or excess fertilizer. A low substrate-EC, compared with Table 2, does not necessarily indicate a problem. This is because vigorously- growing plants can rapidly (within hours) take up fertilizer nutrients into the tissue, especially in small containers such as plugs.

Observing the overall appearance of the plant, checking the fertilizer level being applied, and using your grower experience are equally important. Also check for trends from one week to the next. If EC is tending to increase over time this indicates excess fertilizer application. If EC is stable, plant uptake and applied fertilizer are probably in balance. If EC is decreasing then the plant is taking up more nutrients than the fertilizer level currently being applied.

Table 1. Interpretation of substrate pH levels for container grown crops. Values are the same for all substrate testing methods.

 Acceptable rangeExamples
Iron-inefficient or “Petunia” Group  5.4 to 6.2Arugula, azalea, bacopa, basil, blueberry, calibrachoa, dianthus, nemesia, pansy, petunia, rhododendron, snapdragon, verbena, vinca, and any other crop that is prone to micronutrient deficiency (particularly iron) when grown at high substrate pH.
  General Group  5.8 to 6.4Chrysanthemum, cucumber, impatiens, ivy geranium, lettuce, osteospermum, pepper, poinsettia, tomato, and any other crop that is not generally affected by either micronutrient deficiencies or toxicities.
Iron-efficient or “geranium” group  6.0 to 6.6Lisianthus, marigolds, New Guinea impatiens, seed geraniums, zonal geraniums, and any other crop that is prone to micronutrient toxicity (particularly iron and manganese) when grown at low substrate pH

Table 2. Interpretation of substrate electrical conductivity (EC) or soluble salt levels.

 1:2 MethodSaturated Paste Extract methodPour-through methodPlug squeeze method
Low fertility0 to 0.50 to 1.00 to 2.40 to 2.4
Acceptable range0.6 to 1.51.1 to 3.02.5 to 5.02.5 to 4.0
High fertility>1.5>3.0>5.0>4.0

Values are reported in milliSiemens per centimeter (mS/cm). The units of measure for EC can be mMho/cm, dS/m, mS/cm, µM/cm or mMho x 10-5/cm. The relationship is 1 mMho/cm=1 dS/m=1 mS/cm=1000 µS/cm=100 mMho x 10-5/cm.

video-alkalinity of irrigation water ( dissolved Lime CaCO3)

mg/L or ppm bicarbonates

Week 1: Introduction 
Week 2-1: Light Intensity and quality 1 
Week 2-2: Light intensity and quality 2 
Week 3-2: CO2 
Week 3-1: Photoperiod 
Week 4-1: Wind 
Week 4-2: Temperature 
Week 5-1: Humidity 
Week 5-2: Energy balance 1 
Week 6-1: Canopy environment 1 
Week 5-3: Energy balance 2 
Week 6-2: Canopy environment 2 
Week 7-1: Plant nutrition 
Week 7-2: Substrate 
Week 8-1: Water relation 
Week 8-3: Sink source 2 (cont.) 
Week 8-2: Sink source 1 
Week 9-1: GH environment 1 
Week 9-2: GH environment 2 


UF Institute of Food and Agricultural Sciences Training

substrate nutrition

video-Visualizing Soil Properties: Water Infiltration

OSU Extension – Containers and Media for the Nursery

Growing Media for Container Production in a Greenhouse or Nursery

Media Chemical Properties

Table 1. Typical ranges based on a saturated media extract (SME) analysis.
ParameterTypical Range
EC. .500-3,000 umho/cm
NO3–N. .40- 00 ppm
P. .5-50 ppm
K. .50- 00 ppm
Ca. .30-1 0 ppm
Mg . . . . . . . . . . . . . . .0-75 ppm
Na. .4-80 ppm

Media pH is a critical issue because it plays a major role in determining the availability of many nutrients A common problem occurs in organic-based mixes when the pH falls below 5 0 Below this pH, the availability of Zn and Mn increases dramatically and often results in foliar toxicities from these elements While aluminum toxicity is recognized as a common concern in mineral soils at a low pH, this is usually not a problem in organic-based mixes

Cation Exchange Capacity (CEC)

CEC can vary widely depending on the type of component For example, perlite (1 5 meq/100 gm) and sand have very low CEC values relative to peat and vermiculite (125 meq/100 gm) components Some growers have started to use small volumes (2 to 15 percent) of clay-type amendments (e g , zeolites) in their soilless media These clay amendments may increase a medium’s nutrient retention and improve its physical properties It is important to understand which components have a higher CEC to help develop fertility programs and troubleshoot certain nutrient disorders

Soluble Salts

Similar to media pH, the level of soluble salts that may be tolerated is crop specific The extent of injury will be determined by the plant type, stage in production, longevity of exposure, concentration of salt and irriga- tion practices In general terms, fresh media without fertilizers should have a pour-through EC of less than 750 umho/cm The addition of fertilizer may mean this value is much higher and normal for a particular crop at a specific stage of production

Adjusting Media pH

Raising Media pH

In most cases, nursery and greenhouse growers need to be concerned about raising the media pH since most of the organic media components are acidic The most commonly used material is either calcitic (CaCO3) or dolomitic limestone (mixture of CaCO3 and MgCO3) The amount of lime required will depend on the starting pH, the desired pH, the particle size of the limestone (i e , small particles faster acting than large ones), the type of media and the alkalinity of irrigation water used In general, lime rates generally fall in a range between 5 and

15 lbs/yd3 with rates below 8 pounds most common Calcitic or dolomitic limestone is most reactive when incorporated into the media prior to planting Note that many of the pelletized granular limestone materials are actually fine powders that have been glued together with a binder When these granules or prills are exposed to water, they fall apart into a fine powder These fine powders are faster acting than coarser prills but may also wash out of the bottom

of the pot if the media is coarse textured It is absolutely critical that growers know the starting pH of their mix and then monitor the pH over time to see how their fertilizer and irrigation water influence media pH

Other liming materials include calcium oxide (CaO; quick or burned lime, which is very reactive, caustic and more expensive), hydrated lime [Ca(OH)2; also fast acting, caustic and more expensive], marl, egg or oyster shells and wood ash

Greenhouse growers may wish to try one of the following if the pH needs to be raised once the plants are in production The first option is to apply a flow- able limestone drench Start with a 1 quart per

100 gallons rate Avoid getting this mixture on the foliage if possible The second option involves injecting potassium bicarbonate into the irrigation water Continued use of this method may require a grower to switch to a lower potassium source fertilizer

If you are using liquid fertilization (fertigation), you can increase your media pH by switching from an acid-based fertilizer (high percentage of nitrogen in the ammoniacal form) to basic fertilizers that are based on a higher percentage of the nitrogen in the nitrate form

Lowering Media pH

Only rarely do growers using organic mixes express interest in lowering the media pH Generally, the problem develops from using an irrigation water source that has high alkalinity (>100 ppm CaCO3) In those cases, growers typically choose to install an acid injector Others methods are selected if individual blocks of plants require a lower media pH

Materials such as elemental sulfur, ammonium sulfate and ferrous sulfate have all been used Caution must be used when considering using ammo- nium sulfate and ferrous sulfate as you need to account for the nitrogen and iron that accompanies these materials Aluminum sulfate is also an option but is used only for reducing pH around floristhydrangeas (Hydrangea macrophylla) Growers can also affect media pH by selecting specific forms of nitrogen The use of high ammoniacal-nitrogen based fertilizers can lower the media pH over time

Rate recommendations take into consideration the change in pH and type of media and may be obtained from grower manuals or your Cooperative Extension Service

Managing Substrate EC

Electrical conductivity (EC) is a good estimate for the total soluble salts in a media EC does not provide details on the type or amount of individual salts present High ECs can contribute to poor shoot and root growth The first objective is to determine the source for the elevated salts Typically, this will be from the irrigation water source or from the amount or type of fertilizer used Once the source has been identified, you will want to determine if you can reduce or eliminate that source Media salt concentra- tions are directly impacted by what is called the leaching fraction This value represents the percentage of water that leaves a container relative to what is applied High salt conditions can be effec- tively managed by keeping the leaching fraction high (20 to 30 percent) and not allowing pots to dry out The danger in keeping pots wet is that it can contribute to secondary problems with root rot organ- isms (Consult FSA 0 1, Irrigation Water for Greenhouses and Nurseries, for more information on irrigation water quality )

Disinfecting Media

Three methods are primarily considered for sterilization of media Sterilized media is common in plant propagation and greenhouse operations but is not usually considered in an outdoor nursery simply based on the volume of media required and the bene- fits derived Remember that certain amendments

(e g , perlite, vermiculite) are sterile and, therefore, do not require sterilization Composted pine bark and peat contain populations of suppressive microbes that might be eliminated by sterilization techniques

Steam Pasteurization

Steam pasteurization is commonly found in greenhouse or ground bed production The general recommendation is the exposure to steam (212°F) for 30 to 45 minutes The piles should be small enough so all sections reach at least 180°F Piles too big may take too long to achieve uniform heating You must have an appropriate thermometer handy to effectively monitor the temperature at various places in the pile or bed Over-steaming is possible and should be avoided since this kills beneficial organisms and may cause the release of toxic substances, especially when organic components are involved

An alternative pasteurization process, aerated steam, involves blowing a mixture of steam and air through the media Aerated steam (140° to 175°F) uses less energy and fewer beneficial organisms are likely to be harmed  Steam pasteurization SHOULD NOT be used on media that has had slow-release fertilizer blended into it!

Chemical Fumigation

Chemical fumigation is usually limited to ground beds in cut flower production The primary chemicals used were methyl bromide and vapam Methyl bromide uses were phased out in 2005 Consult your Cooperative Extension Service for current recommendations


Solarization is rarely used because the process may take up to one month even under summer condi- tions requiring tremendous planning for future media needs Solarization is accomplished by spreading moist media to a depth of 6 to 10 inches on a clean surface The pile or row is then covered with clear plastic sheets with the edges sealed to the surface to prevent the loss of heat and moisture

Media Physical Properties

Media physical properties may be determined using simple laboratory methods Media samples can be analyzed by commercial laboratories, or you can make the physical measurements yourself using simple tools Procedures for determining physical properties of horticultural substrates are available at hortsublab/pdf/porometer_manual.pdf.

4 Ways to Calculate Porosity – wikiHow

Weight (Bulk Density)

Media weight is kind of a double-edged sword Ideally growers would like a heavy mix when containers are on the ground in an outdoor nursery to minimize blow-over, but during plant movement and shipping, a lightweight mix is desired Weight or bulk density is usually expressed as lbs/ft3 and reported on a dry basis For outdoor container nurseries, dry bulk density of media might range between 12 to 24 lbs/ft3 (wet bulk density of 70 and 90 lbs/ft3) A nursery media that uses a significant percentage of mineral soil will have a dry bulk density of 40 to 50 ft3 For a greenhouse media, the dry bulk density will be lower and in the range of 8 to 18 lbs/ft3 Air-Filled Porosity

When we fill a container with media, the total volume of space in that container is filled with two things: the solid media components and the spaces or voids between all of the solids (Figure 1) Ideally the total volume of empty pores should be in the range of 50 to 70 percent This is referred to as total porosity The remaining container volume would be filled with the solid growing media (i e , 30 to 50 percent) The total porosity of a media is further composed of two parts: air and water Both components are critical for good plant growth, but not enough of either can limit growth

substrates spaces

Figure 1. The container is filled with the solid media components and the spaces or voids between all of the solids.

For one quart and larger containers the air-filled porosity (percentage of pores filled with air) typically ranges from 10 to 20 percent by volume For a 280- plug tray, an acceptable range in air-filled porosity may fall in the range of 3 to 6 percent by volume Obviously, the container volume influences the inter- pretation of the acceptable values The higher the percentage of air-filled porosity, the more frequently watering will be required Propagation media where aeration and drainage are critical may have an air- filled porosity in the range of 15 to 25 percent

 lumetric Moisture Content (sometimes referred to as Water-Holding Capacity)

As described above, the bulk volume of a container will be filled with either solids or pores These pores or voids are then either filled with water or air A typical range in values for the volumetric moisture content (percentage of the pores filled with water after allowing for free drainage) will be between 45 and 65 percent by volume Volumetric moisture content (VMC) gives a grower some indica- tion of how wet or how dry a media will be Sphagnum peat moss that retains water quite well typically has a VMC of 60 percent, while coarse sand, which does not hold water, might have a VMC of

25 percent As was the case with air-filled porosity, the actual values for VMC need to be interpreted relative to the height of the growing container For example, an acceptable VMC for a 6-inch container might be 45 percent, while for a plug tray 68 percent would be a more typical value The effect of media height on the saturated zone is illustrated in

Substrate Containers contain the same media. Notice, saturated zone (textured area at bottom of each container) is the same regardless of the container height.

Figure . Containers contain the same media. Notice, saturated zone (textured area at bottom of each container) is the same regardless of the container height.

All of these physical parameters can be determined in-house with the aid of a scale or balance The measurements can also be determined by an outside commercial laboratory or with the help of the Cooperative Extension Service

EC by substrate

Graph-Electrical conductivity for various soil substrates

Containers and Media for the Nursery

Porosity: Measuring Pore Space

Pore space is expressed in terms of porosity, which is the percentage of pore space volume for a given substrate volume. You can determine the porosity, air space, and water space in your substrate by following the five steps below.

  1. Determine the volume of the pot used to grow plants. You can usually obtain this from the manufacturer.
  2. Add a water-tight liner (such as a polyethylene wrap) to the outer bottom of the pot. Tape the liner to the pot to prevent any material from draining through the holes.
  3. Pour the substrate to the top of the pot. Make sure to compact the substrate as you would normally do during production. At this point, the substrate volume is equal to the volume of pot.
  4. Add water to the top of the substrate, and carefully monitor how much you add. You want to add water until you completely saturate the substrate — that is, when you start to see a shiny layer of water over the substrate. Cover the pot with a lid and keep it aside for an hour. After one hour, check if you need to add a little more water to saturate the substrate. The total volume of water that you added to saturate the substrate

is equivalent to the total pore space volume.

Use this equation to determine porosity:

Porosity (%) = 100 x Volume of water added to fill Pot with substrate / Volume of Pot

Next, place the pot in a water-tight container and make holes at the bottom of the liner you added in step one. Your goal is to drain the water and collect it in the container. Let the pot drain for 10 to 15 minutes so the water can completely drain out. Then, measure the drained volume of water. This volume is equivalent to the air space volume in the substrate.

Use this equation to determine air space:

Air space = 100 x Volume of water drained / Volume of Pot

The water that is left in the substrate after it drains is the water space (also called maximum water-

holding capacity or container capacity). Once you’ve determined air space, you can determine water space with this equation:

Water space (%) = 100 – Air space(%)

Table 1. The following table provides information about the fractional volume of pore space, air space, and water space in two soilless substrates:

Note AFP has different definitions- some have air + water + solid -100

  ComponentPeat + Bark + Perlite + Vermiculite (P-B-P-V)  Peat + Perlite (P-P)
Solids (%)40.938.6
Porosity (%)59.161.4
Water space (as % total pore space)  72  62
Air space (as % total pore space)  28  38
Note AFP has different definitions- some have air + water + solid -100

Soil Electrical Conductivity

Soil electrical conductivity (EC) measures the ability of soil water to carry electrical current. Electrical conductivity is an electrolytic process that takes place principally through water-filled pores. Cations (Ca2+, Mg2+, K+, Na+, and NH +) and anions (SO 2-, Cl-, NO -, and HCO -) from have higher EC than sandy outwash or alluvial deposits. Saline (ECe ≥ 4 dS/m) and sodic (sodium absorption ratio ≥ 13) soils are characterized by high EC. Scientific literature reported a relationship between EC values measured with commercial sensors and depths to claypan, bedrock, and fragipan. Microtopographic depressions in agricultural fields typically are wetter and accumulate  salts dissolved in soil water carry electrical charges and conduct the electrical current. Consequently, the concentration of ions determines the EC of soils. In agriculture, EC has been used principally as a measure of soil salinity (table 1); however, in non-saline soils, EC can be an estimate of other soil properties, such as soil moisture and soil depth. EC is expressed in deciSiemens per meter (dS/m).

Factors Affecting

Inherent – Factors influencing the electrical conductivity of soils include the amount and type of soluble salts in solution, porosity, soil texture (especially clay content and mineralogy), soil moisture, and soil temperature. High levels of precipitation can flush soluble salts out of the soil and reduce EC. Conversely, in arid soils (with low levels of precipitation), soluble salts are more likely to accumulate in soil profiles resulting in high EC. Electrical conductivity decreases sharply when the temperature of soil water is below the freezing point (EC decreases about 2.2% per degree centigrade due to increased viscosity of water and decreased mobility of ions). In general, EC increases as clay content increases. Soils with clay dominated by high cation-exchange capacity (CEC) clay minerals (e.g., smectite) have higher EC than those with clay dominated by low CEC clay minerals (e.g., kaolinite). Arid soils with high content of soluble salt and exchangeable sodium generally exhibit extremely high EC. In soils where the water table is high and saline, water will rise by capillarity and increase salt concentration and EC in the soil surface layers.

It is generally accepted that the higher the porosity (the higher the soil moisture content), the greater the ability of soil to conduct electrical currents; that is, other properties being similar, the wetter the soil the higher the EC. Soil parent materials contribute to EC variability. Granites have lower EC than marine shales and clayey lacustrine deposits organic matter and nutrients and therefore have higher EC than surrounding higher lying, better drained areas.

Dynamic – Mineral soils enriched in organic matter, or with chemical fertilizers (e.g., NH4OH) have higher CEC than non-enriched soils, because OM improves soil water holding capacity, and synthetic fertilizers augment salt content. Continuous application of municipal wastes on soil can increase soil EC in some cases. Electrical

conductivity has been used to infer the relative concentration, extent, and movement of animal wastes in soils. Because of its sensitivity to soluble salts, EC is an effective measure for assessing the contamination of surface and ground water. Although EC does not provide a direct measurement of specific ions or compounds, it has been correlated with concentrations of potassium, sodium, chloride, sulfate, ammonia, and nitrate in soils. Poor water infiltration can lead to poor drainage, waterlogging, and increased EC.

Relationship to Soil Function

Soil EC does not directly affect plant growth but has been used as an indirect indicator of the amount of nutrients available for plant uptake and salinity levels. EC has been used as a surrogate measure of salt concentration, organic

Table 1. Classes of salinity and EC (1 dS/m = 1 mmhos/cm; adapted from NRCS Soil Survey Handbook)

EC (dS/m)Salinity Class
0 < 2Non-saline
2 < 4Very slightly saline
4 < 8Slightly saline
8 < 16Moderately saline
≥ 16Strongly saline

matter, cation-exchange capacity, soil texture, soil thickness, nutrients (e.g., nitrate), water-holding capacity, and drainage conditions. In site-specific management and high-intensity soil surveys, EC is used to partition units of management, differentiate soil types, and predict soil fertility and crop yields. For example, farmers can use EC maps to apply different management strategies (e.g., N fertilizers) to sections of a field that have different types of soil. In some management units, high EC has been associated with high levels of nitrate and other selected soil nutrients (P, K, Ca, Mg, Mn, Zn, and Cu).

Most microorganisms are sensitive to salt (high EC). Actinomycetes and fungi are less sensitive than bacteria, except for halophyte (salt-tolerant) bacteria. Microbial processes, including respiration and nitrification, decline as EC increases (table 2).

Problems with Poor Soil EC Levels

High EC can serve as an indication of salinity (EC > 4 dS/m) problems, which impede crop growth (inability to absorb water even when present) and microbial activity (tables 2 and 3). Soils with high EC resulting from a high concentration of sodium generally have poor structure and drainage, and sodium becomes toxic to plants.

Improving Soil EC

Effective irrigation practices, which wash soluble salts out of soil and beyond the rooting depth, can decrease EC. Excessive irrigation and waterlogging should be avoided since a rising water table may bring soluble salts into the root zone. In arid climates, plant residue and mulch help soils to remain wetter and thus allow seasonal precipitation and irrigation to be more effective in leaching salts from the surface. To avoid the adverse effects of high EC (salinity) in irrigation water, the leaching requirement must be calculated for each crop. Leaching requirement is the fraction of water needed to flush excessive salt below the root zone, that is, the amount of additional water required to maintain a target salinity level. Adding organic matter,

such as manure and compost, increases EC by adding cations and anions and improving the water-holding capacity. In some cases, a combination of irrigation and drainage is necessary to lower salt concentration and EC. An EC water (ECw) ≤ 0.75 dS/m is considered good for irrigation water. Beyond this value, leaching or a combination of leaching and drainage will be necessary if the water is used.

Measuring Soil EC

The EC pocket meter is used to take measurements in the field. The method is described in the Soil Quality Test Kit Guide. Always calibrate the EC meter before use.

The pocket meter can be augmented by a probe that is placed directly into the soil to measure subsoil EC and NO – and make other estimates. NRCS soil scientists and agronomists use electromagnetic induction meters, not pocket EC meters, to map spatial variability of EC and associated soil properties at field scales. Special sensors are used for EC mapping for precision agriculture.

Table 2. Influence of soil EC on microbial process in soils amended with NaCl or nitrate (adapted from Smith and Doran, 1996)
  Microbial process  Salt addedEC Range (dS/m)Relative Decrease (%)Threshold EC (1:1)
RespirationNaCl0.7 – 2.817 – 470.7
DecompositionNaCl + alfalfa0.7 – 2.92 – 250.7
Nitrificationsoil + alfalfa0.7 – 2.910 – 370.7
DenitrificationNO3-N1 – 1.832 – 881
Table 3. Salt tolerance of crops and yield decrease beyond EC threshold (adapted from Smith and Doran, 1996)
  Crop speciesThreshold EC 1:1 (dS/m)*Percent yield decrease per unit EC beyond threshold EC
Alfalfa1.1 – 1.47.3
Barley4.5 – 5.75.0
Cotton4.3 – 5.55.2
Peanut1.4 – 1.829
Potato1.0 – 1.212
Rice1.7 – 2.112
Soybean2.8 – 3.620
Tomato1.4 – 1.89.9
Wheat3.9 – 5.07.1
* Electrical conductivity of a 1:1 soil/water mixture relative to that of a saturated paste extract
Soil Quality Indicators: Soil Electrical ConductivityUSDA
Soil Electrical ConductivityUSDA
Using Soil Electrical Conductivity (EC) to Delineate Field VariationOhio State University
Pour-through Technique of Measuring Electrical Conductivity of the SubstratePurdue University
Commercial Greenhouse Production: pH and Electrical Conductivity Measurements in Soilless SubstratesPurdue University


A Nursery Friendly Method for Measuring Air Filled Porosity of Container Substrates

Bilderback-NC State

  1. Porometer construction: Measuring air-filled porosity requires an apparatus called a porometer. Therefore, the first step is to construct porometers
  2. Pre-moistening Substrate to Be Tested. Pre-moistening 12–24 h before testing is critical for achieving uniform and consistent results.
  3. Packing Porometers with Substrate: After removing the plastic carton tops, individually weigh each porometer and record the weight. The weight of the plastic carton is subtracted from filled cartons as a “tare” weight to provide an accurate mass of substrate in each porometer. Next, overfill each porometer with potting substrate; tap each porometer firmly 3–5 times on a table or bench to eliminate air pockets and establish a bulk density
  4. Saturate Substrate in Porometers: After packing, porometers are set upright in a vessel large enough for all of the test porometers to stand erect and tall enough to add water to the top of the porometers
  5. Collecting and Measuring Drainage: Saturation of each porometer can be observed when water is seen at the surface of the substrate. Drainage from each porometer must be measured individually. This step may require practice. Fingers are used to prevent leaking from the drainage holes while the porometer is lifted from the saturation vessel and a pan is quickly placed under the drain holes. Porometers can be balanced on supports placed in the bottom of the drainage pan and allowed to fully drain. After draining has stopped, the drained volume is measured and recorded for each porometer
  6. Calculating air filled porosity: The drainage volume is divided by the total volume for each porometer to determine a percent air-filled porosity (Table 1). Air-filled porosity measurements are added and divided by the number of porometers to obtain an average AFP for each test substrate. Changes in air filled porosity during a growing season or over a production cycle can be measured by placing porometers packed with substrate in containers which are set in nursery growing beds. Decomposition shrinkage should be measured and marked from the top of the porometer. The volume of the porometer marked at the surface of the substrate would be used as the new total volume and calculations followed as described above. If the important steps for pre- moistening samples and for packing to match the weight of each replicate sample in porometers are followed, consistent results can be accomplished.

Monitoring electrical conductivity in soils and growing media

What is EC? EC is a measure of the salinity (total salt level) of an aqueous solution. Pure, distilled water is a perfect insulator and it’s only because of dissolved ions that it can conduct electricity at all (Figure 1A). An EC meter measures the electrical charge carried by the ions that are dissolved in a solution— the more concentrated the ions, the higher the reading.

In nurseries, dissolved ions come from two sources (Figure 1B). First, all irrigation water contains some salt ions as rain water trickles through the soil and rocks.

The amount of the “background” salinity is a function of the local geology and climate. Soils and parent material  have a major effect. Soils derived from marine sediments will contain high levels of sodium, chloride and sometimes boron. Water running through calcareous rocks or soils picks up calcium, magnesium and bicarbonate ions. Irrigation water from dry climates will have higher salinity than water from a humid climate. This only makes sense because, when water evaporates, the dissolved salts are left behind and the remaining solution would have a higher EC reading.

The second source of salinity in soils or growing media is from added fertilizers (Figure 1B). The release of salts varies considerably depending on how you are fertilizing. When fertigating, the soluble fertilizer that you inject into the irrigation water can be measured immediately. In fact, the best way to check the accuracy of your injector is to measure the EC of the applied fertigation solution. If you are incorporating controlled-release fertilizers into the soil or growing medium, however, then the salts are released according to fertilizer coating, water levels, and temperature. Most solid organic fertilizers release their nutrients very slowly and are less temperature or moisture dependent. Liquid organics release nutrients more rapidly but still much slower than soluble fertilizers.

EC Units. The physics and politics of this subject are complicated but think of it this way. We’re measuring electrical conductance which is the inverse of resistance. The unit of resistance is an ohm, and just to be cute, they call the unit of conductance a mho (pronounced “mow”), which is ohm spelled backwards. The most commonly used EC units in horticulture are micromhos per centimeter (µhos/cm), and the SI units of microsiemens per centimeter (µS/cm) which are equivalent. Because electron activity is strongly dependent on temperature, all EC measurement must be adjusted to a standard temperature of 77 °F (25 °C

Saturated Media Extract (SME). This technique is the laboratory standard that is used by commercial soil and water testing laboratories. If you are interested in absolute EC values, this is the only choice. The SME method uses saturation as the standard soil or media

The use of controlled-release fertilizers (CRF) has complicated the measurement of EC. Because the prills are very fragile, even collecting a sample or squeezing it can damage them. Broken prills will release all their fertilizer salts at once and artificially elevate the EC reading. Thus, some of the EC monitoring procedures should not be used when incorporating CRF

Pour-Through. This is a relatively new technique for measuring EC in containers, and works for all container types except for miniplugs where their short height stops the media solution from freely draining. It would also be impractical for very large containers which are difficult to move (Table 1). The pour-through process consists of 2 steps (Figure 4). First, medium in a container is progressively irrigated until saturated, and then left to stand for about 2 hours. Or, just do the procedure 2 hours after irrigation. Next, pour a volume of distilled water onto the media surface to produce about 100 ml of leachate. Of course, this depends on container volume and type of growing media. Make sure and apply the water slowly enough that it doesn’t run off and down the insides of the container. The idea is to have the applied water force out the solution surrounding the roots. The pour-through technique is ideal for growing media with controlled-release fertilizers because the prills are not squeezed or otherwise damaged (Table 1). Therefore, this method is ideal for outdoor growing compounds where controlled release fertilizers are the standard.

Figure 4 – The pour-through technique works for all containers except miniplugs and larges sizes, and is ideal when using controlled-release fertilizers

EC pour through technique

video-Pour Through Method for pH and EC

video-Hanna Lab – Set Up and Calibrate the Hanna Instruments pH, EC, TDS Combo Tester HI98129

video-Substrate Water Holding Capacity



Dry Bulk Density:

 ρb = Ms / Vt

Where, ρb = Dry Bulk Density,  Ms = Mass of Soil Vt = Volume

Wet Bulk Density:

 Pt = (Msolid+Mliquid)/Vtotal

Where, Pt = Wet Bulk Density Msolid = Mass of Solids Mliquid = Mass of Liquid Vtotal = Total Volume

Moisture Content :

w = (Mw / Ms) * 100

Where, w = Moisture Content Mw = Mass of Water in Soil Ms = Dry Mass of Soil

Soil void ratio (e) is the ratio of the volume of voids to the volume of solids:

e = (V_v) / (V_s)

Where V_v is the volume of the voids (empty or filled with fluid), and V_s is the volume of solids.

soil porosity (n)  is defined as the ratio of the volume of voids to the total volume of the soil. The posoity and the void ratio are inter-related as follows:

e = n /(1-n) ,  and n = e / (1+e)

The value of void ratio depends on the consistence and packing of the soil. It is directly affacted by compaction. Some typical values of void ratio for different soils are given below:

DescriptionUSCSVoid ratio [-]Reference
min maxSpecific value
Well graded gravel, sandy gravel, with little or no finesGW0.260.46 [1],
Poorly graded gravel, sandy gravel, with little or no finesGP0.260.46 [1],
Silty gravels, silty sandy gravelsGM0.180.28 [1],
Gravel(GW-GP)0.300.60 [2], 
Clayey gravels, clayey sandy gravelsGC0.210.37 [1], 
Glatial till, very mixed grained(GC)0.25[4 cited in 5]
Well graded sands, gravelly sands, with little or no finesSW0.290.74 [1], [2], 
Coarse sand(SW)0.350.75 [2], 
Fine sand(SW)0.400.85 [2], 
Poorly graded sands, gravelly sands, with little or no finesSP0.300.75 [1], [2], 
Silty sandsSM0.330.98 [1], [2], 
Clayey sandsSC0.170.59 [1], 
Inorganic silts, silty or clayey fine sands, with slight plasticityML0.261.28 [1], 
Uniform inorganic silt(ML)0.401.10 [3], 
Inorganic clays, silty clays, sandy clays of low plasticity CL0.410.69 [1], 
Organic silts and organic silty clays of low plasticityOL0.742.26 [1], [3], 
Silty or sandy clay (CL-OL)0.251.80 [3], 
Inorganic silts of high plasticity MH1.142.10 [1], 
Inorganic clays of high plasticity CH0.631.45 [1], 
Soft glacial clay1.20[4 cited in 5]
Stiff glacial clay0.60[4 cited in 5]
Organic clays of high plasticity OH1.063.34 [1], [3], 
Soft slightly organic clay(OH-OL)1.90[4] cited in [5]
Peat and other highly organic soilsPt [4 cited in 5]
soft very organic clay(Pt)3.00[4] cited in [5]


Factors Affecting Porosity of Soil:

Wide difference in the total pore space of various soils occurs depending upon the following several factors:

(i) Soil Structure:

A soil having granular and crumb structure contains more pore spaces than that of prismatic and platy soil structure. So well aggregated soil structure has greater pore space as compared to structure less or single grain soil.

(ii) Soil Texture:

In sandy soils the total pore space is small whereas in fine textured clay and clayey loam soils total pore space is high and there is a possibility of more granulation in clay soils.

(iii) Arrangement of Soil Particles:

When the sphere like particles is arrangement in columnar form (i.e. one after another on the surface forming column like shape) it gives the most open packing system resulting very low amount of pore spaces. When such particles are arranged in the pyramidal form it gives the most close packing system resulting high amount of pore spaces.

(iv) Organic Matter:

Soil containing high organic matter possesses high porosity because of well aggregate formation.

(v) Macro-Organisms:

Macro-organisms like earthworm, rodents, and insects etc. increase macro-pores in the soil.

(vi) Depth of Soil:

With the increase in depth of soil, the porosity will decrease because of compactness in the sub-soil.

(vii) Cropping:

Intensive crop cultivation tends to lower the porosity of soil as compared to fallow soils. The decrease in porosity may be due to reduction in organic matter content.

(viii) Puddling:

Due to puddling under sufficient soil moisture, the soil surface layer is made dense and compact. Eventually, the porosity of this surface soil is reduced by the infiltration of muddy surface materials.


Although it may seem counter-intuitive, the small pore spaces of clay add up to more total void space than the fewer number of large pore spaces in sand. Consequently, in light rain or slow snowmelt, clay may be able to hold more water than sand.

pore space

However, water drains from clay soil more slowly than from sandy soils. So in successive rain events, clay soils may remain saturated between storms and therefore produce more runoff in the later rain events.

infiltration, percolation
High permeability. Low permeability.

More References

CuttingsNutrient supply during cutting propagation.pdf
Hydroponic Nutrients
hydro-Hochmuth Hydroponic Tomato Fertilizer.pdf
Nutrients-recirculating solutions.pdf
planting substrates

plant fertilizer calculation videos 4

See Fertilizer Chemistry

Example Fertilizer Calculation N, P2o5, K20

Maxibloom Fertilizer Label

bove is an example of a nutrient labels guaranteed analysis.
It tells us how much of each element is in the bag at percentage weight by volume (%w/v).
This provides us with enough information to establish a reasonably accurate ppm.

Note that analyzing the ppm from fertilizer labels won’t provide 100% accurate ppms.
Fertilizers sold worldwide are often only required to be listed accurately to within 0.4%.

Regulations around the world require that NPK.. values be presented somewhat ambiguously.
Therefore, listings for the same nutrient may appear to vary on a country-by-country basis.
For example, when looking at our labels guaranteed analysis you will find note that it states;

Available Phosphate (P2O5)……….15.0%
Available Potash (K2O)…………..14.0%

This information becomes important when interpreting the guaranteed analysis.

That is, it is important to note that the P and K numbers found on the guaranteed analysis do not always reflect the actual amounts of elemental phosphorous and potassium by %.

With our label, this is the case and P is listed as P2O5 (phosphorous pentoxide) and K is listed as K2O (potassium oxide) percentage.

When phosphorus is listed as P2O5 it is only 43% elemental P and when potassium is listed as K2O it is only 83% elemental K.

Therefore, when this system is in use, a 5-15-14 NPK ratio truly reflects elemental NPK 5-6.45-11.62.

N = 5
P = 15 * 0.43 = 6.45
K = 14 * 0.83 = 11.62

Additionally, other nutrients such as calcium (Ca), magnesium (Mg) and sulfur (S) can be listed in their oxide form (CaO, MgO, SO3) or in elemental form, or both.
To convert other nutrient listings that may appear on some labels use these equations.

CaO to Ca multiply by 0.714
MgO to Mg multiply by 0.6031
SO3 to S multiply by 0.4

Percentage Weight by Volume (%w/v)

A simple way of understanding how to convert a %w/v listing found on the guaranteed analysis into grams per litre is by understanding that 1ml of RO water weighs 1gram.

Percentage weight by volume %w/v refers to the total weight of elements contained within a finished concentrate of a given total volume.

For example, 5% of nitrogen added to 1 litre(1000ml) of RO water would mean that there is 50grams of N in the water.

1000 (ml) * 0.05 (5% nitrogen) = 50 (grams of N)

Converting %w/v to ppm and ppm to %w/v

To establish ppm from %w/v you simply need to multiply by 10000.
5% (nitrogen) * 10000 = 50000 (ppm)
To establish %w/v from ppm you simply need to divide by 10000.
50000 (ppm) / 10000 = 5% (nitrogen)

To establish the concentration of individual elements in the water, the guaranteed analysis (%w/v) should first be converted into ppm, then multiplied by the usage rate (per litre), then divided by 1000 (ml).

For example, if a nutrient lists 5% nitrogen, when it is used at 5grams per 4 litres it will yield 62.5 ppm of nitrogen per litre.

Step 1 : 5% (nitrogen) * 10000 = 50000 (ppm)
Step 2 : 5grams / 4L = 1.25g/litre
Step 3 : (50000 (ppm) * 1.25g/litre) / 1000ml (1 litre) = 62.5ppm of nitrogen per litre (1000ml)

Doing the math

Using what we’ve learned, we’re finally ready to find the ppm of our fertilizer.

5 * 10000 = 50k nitrogen ppm
6.45 * 10000 = 64.5k phosphorus ppm
11.62 * 10000 = 116.2k potassium
5 * 10000 = 50k calcium ppm
3.5 * 10000 = 35k magnesium ppm
4 * 10000 = 40k sulfur ppm
0.1 * 10000 = 1k iron ppm

50k + 64.5k + 116.2k + 50k + 35k + 40k + 1k = 356,7k or 356700 ppm.
(356700ppm * 1.25g/litre) / 1000ml = 445ppm(~0.9EC) per litre.

How Much Phosphorus and Potassium are Really in Your Fertilizer?

Fertilizer Calculations for Greenhouse Crops

Understanding phosphorus fertilizers

Common Fertilizers Table

Table 1: Percentages of water-soluble and available phosphate in several common fertilizer source

P2O5 sourceNTotalAvailableP2O5Water soluble* P2O5
Superphosphate (OSP)0%21%20%85%
Concentrated Superphosphate (CSP)0%45%45%85%
Monoammonium Phosphate (MAP)11%49%48%82%
Diammonium Phosphate (DAP)18%47%46%90%
Ammonium Polyphosphate (APP)10%34%34%100%
Rock Phosphate0%34%38%0%
*Water-soluble data are a percent of the total P2O5.
Source: Ohio Cooperative Extension Service.

More Fertilizer Calculation Examples with Videos

Fertilizer calculation one
% weight15515
desired ppm =  mg/L or mg/kghoal
( 1 liter oof water weighs 1 kg)200mg/L
0.15 mg of N per mg og Fertilizer
 200 / 0.15 =
mg N / L   /   mg N/ mg F = 
 mg F / L ) for desired 200 ppm)
 divide by 1000 to get grans
1.333333333 g per L
for 2000 L solution2000
2666.666667grams F in 2000 L1000
2.666666667kh of F in 2000 L
Fertilizer calculation two
1 gallon = 3.7854 L
5000gallon holding tank
* 3.79
     18,950.00Liters storage tank
Calcium Nitrate0.155
15.5 % Nmh N per Mg Ca Bitrate
desired ppm 100 )mg/L)0.64516129grams
     12,225.81times storage tank


Fertilizer calculation one
Fertilizer calculation two
Fertilizer calculation three
Fertilizer calculation four
Introduction to Plant Growth Regulators Unit 2017
Growth Reg Calc One
Growth Reg Calc Two
Growth Reg Calc Three
Growth Reg Calc Four
Growth Reg Calc Five
Introduction to Lighting Unit 2017
Quantum Flux Density 2017
Quantum flux density and DLI 2017
Introduction to Glazings Learning Unit 2017
Introduction to Atmospheres Learning Unit 2017
Introduction to Cooling Learning Unit 2017
Heating Learning Unit 2017
Mineral Nutrition Unit Intro 2017
Intro to Substrates Learning Unit 2017
Understanding Electrical Conductivity 2017

Other Nutrients


Common nameChemical name (Formula)
Potash fertilizerc.1942 potassium carbonate (K2CO3); c.1950 any one or more of potassium chloride (KCl), potassium sulfate (K2SO4) or potassium nitrate (KNO3).[9][10] Does not contain potassium oxide (K2O), which plants do not take up.[11] However, the amount of potassium is often reported as K2O equivalent (that is, how much it would be if in K2O form), to allow apples-to-apples comparison between different fertilizers using different types of potash.
Nitrate of potash or saltpeterpotassium nitrate (KNO3)
Sulfate of potash (SOP)potassium sulfate (K2SO4)
Permanganate of potashpotassium permanganate (KMnO4)

Potassium oxide (K2O) is an ionic compound of potassium and oxygen. The chemical formula K2O (or simply ‘K’) is used in several industrial contexts: the N-P-K numbers for fertilizers,


Phosphorus pentoxide is a chemical compound with molecular formula P4O10 (with its common name derived from its empirical formula, P2O5).

The phosphate or orthophosphate ion [PO 4]3− is derived from phosphoric acid by the removal of three protons H+


Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil additive made from pulverized limestone or chalk. The primary active component is calcium carbonate.. Calcium oxide (CaO), is commonly known as quicklim.e

Calcareous (/kælˈkɛəriəs/) is an adjective meaning “mostly or partly composed of calcium carbonate“, in other words, containing lime or being chalky.

Calcium carbonate shares the typical properties of other carbonates. Notably it

CaCO3(s) + 2 H+(aq) → Ca2+(aq) + CO2(g) + H2O(l)

Calcium carbonate reacts with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.

CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)

Agriculture and aquaculture

Agricultural lime, powdered chalk or limestone, is used as a cheap method for neutralising acidic soil, making it suitable for planting, also used in aquaculture industry for pH regulation of pond soil before initiating culture.[54]


Ammonia is a compound of nitrogen and hydrogen with the formula NH3.

The ammonium cation is a positively charged polyatomic ion with the chemical formula NH+ 4. It is formed by the protonation of ammonia (NH3).

Urea, also known as carbamide, is an organic compound with chemical formula CO(NH2)2.

soil reactions

plant videos 3 physiology


1BIOPL3420 – Plant Physiology
BIOPL3420 – Plant Physiology – Lecture 01 
BIOPL3420 – Plant Physiology – Lecture 02 
BIOPL3420 – Plant Physiology – Lecture 03 
BIOPL3420 – Plant Physiology – Lecture 04 
BIOPL3420 – Plant Physiology – Lecture 05 
BIOPL3420 – Plant Physiology – Lecture 06 
BIOPL3420 – Plant Physiology – Lecture 07 
BIOPL3420 – Plant Physiology – Lecture 08 
BIOPL3420 – Plant Physiology – Lecture 09 
BIOPL3420 – Plant Physiology – Lecture 10 
BIOPL3420 – Plant Physiology – Lecture 11 
BIOPL3420 – Plant Physiology – Lecture 12 
BIOPL3420 – Plant Physiology – Lecture 13 
BIOPL3420 – Plant Physiology – Lecture 14 
BIOPL3420 – Plant Physiology – Lecture 15 
BIOPL3420 – Plant Physiology – Lecture 16 
BIOPL3420 – Plant Physiology – Lecture 17 
BIOPL3420 – Plant Physiology – Lecture 18 
BIOPL3420 – Plant Physiology – Lecture 20 
BIOPL3420 – Plant Physiology – Lecture 21 
BIOPL3420 – Plant Physiology – Lecture 22 
BIOPL3420 – Plant Physiology – Lecture 23 
BIOPL3420 – Plant Physiology – Lecture 24 
BIOPL3420 – Plant Physiology – Lecture 25 
BIOPL3420 – Plant Physiology – Lecture 26 
BIOPL3420 – Plant Physiology – Lecture 27 
BIOPL3420 – Plant Physiology – Lecture 28 

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UF Daily Light Integral app in

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Photosynthesis | MIT 7.01SC Fundamentals of Biology

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In the Break Room: Starting Strong with Seed Propagation

In the Break Room: Starting Strong with Vegetative Propagation

In the Break Room: Perennial Production Tips & Tricks

Growing a Better Liner: Video 1 – From Box to Bench

Growing a Better Liner: Video 2 – Ensuring a Good Start

Growing a Better Liner: Video 3 – Rooting Stages 1 and 2

Growing a Better Liner: Video 4 – Rooting Stages 3 and 4


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