Greenhouse Structures.

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A plant cannot complete its life cycle without certain mineral elements to live, grow, and reproduce. Plants need 17 elements: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), which are derived from the CO2, H2O, and N2 in the atmosphere and potassium (K), calcium (Ca), magnesium (Mg), phosphorous (P), sulphur (S), iron (Fe), copper (Cu), manganese (Mn), zinc (Zn), molybdenum (Mo), boron (B), chlorine (Cl), and nickle (Ni) which are found in the soil.

Plants cannot use atmospheric nitrogen. Nitrogen in the soil as nitrate or ammonium is carried there mainly by rain from the atmosphere where it was formed by lightning or ultraviolet radiation (UV) and microbial fixation in the soil. Microbial nitrogen fixation is facilitated by free living bacteria (examples: cyanobacteria, clostridium, azotobacteria) in the soil, by rhizobium in association legume root nodules, and actinomycetes in a symbiotic relationship with actinorhizal plants (about 21 genera of non-legumes with the ability to form root nodules with Frankia, a N2-fixing actinomycete.).

Essential mineral nutrients are divided into the macronutrients (mineral required in larger amounts, 0.5% or more of dry wt.) and the micronutrient or trace elements, required in much smaller quantities (usually a few parts per million). Of the soil derived elements, Fe, Cu, Mn, Zn, Mo, B. Cl, and Ni, are micronutrients; the rest are macronutrients. When an element is missing, plants respond by characteristic visual symptoms including stunted growth; thus, being able to recognize these symptoms is essentially in determining how and when to fertilize crops. The ability to recognize mineral deficiency or toxicity in plants is especially important in the closed, controlled environment of the greenhouse because the plants do not have access to the soil where these minerals occur naturally.

In addition to the essential elements, there are also nonessential, but sometimes beneficial elements - silicon (Si), cobalt (Co), selenium (Se), and sodium (Na). Take a look at this periodic table of elements from the Department of Soil Science at the University of Wisconsin-Madison that highlights the essential and beneficial elements.

When all the essential elements or mineral nutrients are available, no difficulties arise for the plant. However, if an element is missing it can sometimes be obtained from the breakdown of preformed molecules in old plant cells. These mobile elements are transported to the young growing tissues by the phloem (which is made up of different cell types that transport organic compounds, help regulate metabolic activities, provide mechanical strength, and store compounds). This causes the appearance of mineral deficiency symptoms to appear first in the older leaves and speeds their senescence (death). For example, when a young plants' cotyledons and lower leaves turn yellow and die this may be an indication of the mobile mineral N being degraded from amino acids in the older leaves to the young leaves because of the lack of N in the plant's soil media.

Some mineral elements become "fixed" in a plant cell and cannot be removed; they are immobile. Symptoms of deficiency of non-mobile elements show up in the youngest leaves. For example, iron is needed for chlorophyll synthesis; therefore, when it is lacking, the younger leaves become chlorotic (yellowish) because they don't have the green pigment.

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I. Mineral Nutrients

Because they are required in the greatest quantities, N, P, and K are the primary constituents in most complete plant fertilizers. So called organic fertilizers supply these elements from the breakdown of organic matter such as animal manures, etc. Hence, organic fertilizers tend to be slow release compared to inorganic fertilizers, which consist of the pure (non-organic) nutrient elements or inorganic compounds such as NO3, NH4, P2O5, KCL, etc.

• Deficiency/Toxicity Symptoms

  Nutrient deficiency and toxicities among plants are different depending on the species and variety of your plant material. Besides the amount of a particular mineral in the soil media, other factors affect the availability of minerals to plants. For example, The pH (measure of the concentration of hydrogen ions in a
  substance) of the soil media determines to a great extent the chemical forms in which many plant nutrients exist. Some of these forms are more or less soluble, depending on the nutrient. In cases of extreme pH ranges in either direction, some of the micronutrients are unavailable, while others are available in toxic quantities. (WP)

  There are five symptoms to look for when diagnosing plant mineral deficiencies or toxicity:

• Chlorosis - yellowing of leaves.
• Necrosis - dead plant tissue.
• Anthocyanin (pigment responsible for many of the blue, red and purple colors in plants) accumulation
• Lack of new growth
• Stunting

Take a look at geranium plants showing micronutrient toxicities from Ohio State University's Department of Floriculture.

Mineral	Deficiency Symptoms	Toxicity Symptoms	Leachability	Mobility
Primary Macronutrients
Nitrogen (N)	Most common nutrient deficiency; stunted growth; yellowing older leaves; lower leaves dry up. example	Dark green foliage;	Leachable, especially NO3-.	Mobile in plant and soil
Phosphorous (P)	stunted growth; distorted dark green leaves with necrotic spots; purplish leaves due to anthocyanin accumulation. example	Clorosis, may cause iron and maganese deficiencies	Normally not leachable, but may leach from soil high in bark or peat.	Mobile in plant, Immobile in soil
Potassium (K)	Interveinal chlorosis on older leaves with marginal and tip necrotic lesions; curling or crinkling example		Leachable in sandy soils.	Mobile in plant
Secondary Macronutrients
Calcium (Ca)	Growing tips die; hooked leaf tips; small leaves; poor fruit development. example		Normally not leachable.	Moderately limited mobility in plants.
Sulfur (S)	Chlorosis on younger leaves that progresses to older leaves; some anthocyanin accumulation. example		Leachable.	Not mobile in plants.
Magnesium (Mg)	Interveinal chlorosis and bronze coloration on older leaves; thin, brittle leaves; Curling upward of edges and tips of leaves; poor fruit development. example		Leachable.	Mobile
Micronutrients
Iron (Fe)	Interveinal chlorosis in younger leaves; example			Limited mobility
Copper (Cu)	Wilted younger leaves and terminal bud; Necrotic tips on dark green leaves; small leaves; multiple buds formed.
Manganese (Mn)
Zinc (Zn)
Boron (B)
Molybdenum (Mo)
Chlorine (Cl)
Nickel (Ni)
Nonessential, but sometimes beneficial, elements
Sodium (Na)
Silicon (Si)
Selenium (Se)
Cobalt (Co)

Some other elements may become toxic to plants if they are in great enough amounts:

Element	Toxicity Symptoms
Iodine (I)	Necrosis on leaf margins; older leaves exibit chlorosis and fall off.
Bromine
Flourine	Interveinal chlorosis and necrosis on leaf margins
Aluminum	Interferes with phosporous uptake so will see phosporous deficiency symptoms
Chromium	Small necrotic lesions on brownish-red, narrow leaves.
Lead	Replaces calcium, look for calcium deficiency symptoms.
Cadium	Replaces zinc, look for zinc deficiency symptoms.

NUTRIENTS WITH SIMILAR DEFICIENCY SYMPTOMS

Nutrient Management: the key to growing healthy nursery crops in containers
Micronutrient Disorders

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II. The fertilizer bag

It is important to understand what kinds of information you can get off the bag. Lots of valuable information is required by law to be displayed on any brand of fertilizer, similar in importance to the information available on the label of a pesticide. After explaining the fertilizer bag label, we'll follow up by looking at some dry fertilizers. What they feel like, what they smell like, etc. because there are differences, and there are other ways of looking at a fertilizer to determine just exactly what it is. Primarily, you want to make sure you have the proper signage on the bags and on the containers that they are stored in so that there is absolutely no question about what the material is in that bag.

This is a bag of Excel fertilizer. The first, and one of the most important things on the label are the three numbers 15-5-15, the fertilizer analysis, which refers to the percent of nitrogen, phosphorous, and potassium or NPK. In this case ther is 15 % nitrogen, 5% phosphorous and 15% potassium. Next, let's look at the label on the back of the bag and see what kind of information you can get . The label tells us what the fertilizer is derived from, or what chemical compounds are used to supply the NPK in the percentages indicated.

The label also tells us the amount of various nutrient compounds actually in the bag (in addition to NPK), and how much (in parts per million, ppm) of each there is in a solution of this fertilizer that has 100 ppm of total N. This table also gives recommended rates for continuous or periodic "feeding" (fertilization) of a number of common crops. We see what they recommend for bedding plants, cut flowers, potted Chrysanthemum, Easter lilies, etc.

Probably even more important is the dilution ratio and the amount of fertilizer that you want to mix in a given amount of stock solution of water. Here we see ounces of 15-5-15 to be dissolved in a gallon of concentrate stock solution. For example, if you want to have one hundred ppm of nitrogen you find this number in the left hand column and read across to the weight of the fertilizer to use for the proportioner you will be using. For one hundreds parts per million nitrogen, if you are using a 1-100 proportioner you would use 9 ounces of fertilizer from the bag dissolved in a gallon of water.

So you can obtain a lot of information from these bags. You should look them over so you know exactly what your getting, exactly where you should use it, and exactly how much you want to put on the plant material you are growing in your greenhouse.

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What is a fertilizer proportioner anyway? It is a device which injects a small amount of fertilizer concentrate into the water that is applied to your plant as part of a liquid feed/fertigation program; as opposed to granular or pelletized fertilizers which are applied in dry forms. We will discuss specific types of proportioners later in this chapter after we examine some basic liquid fertilizer techniques, concepts, and terms.

• Liquid Feed/Fertigation
  

  Liquid feed (also called fertigation) is a concentrated liqiud of soluble nutrients that is carried through the irrigation system. Liquid feeding/fertigation usually involves fertilizing at every watering, although it is possible to apply a liquid feed at less frequent intervals. When you fertilize at every watering, you use a lower concentration of fertilizer more often (every watering) than if you are fertilizing periodically with either a liquid or a dry fertilizer. Liquid fertilizing is more constant and uniform from day to day because we put fertilizer on the plant material every time we water, compared to applying fertilizers on a weekly, biweekly, or monthly schedule. This has the advantage that when you do your soil testing to analyze for nitrogen, phosphorous, and potassium you get more uniform readings. When applying fertilizer at every watering there is no feast or famine. Over a long period of time, the plants receive the same amount of fertilizer at a lower rate. There are other methods for putting fertilizer on at a higher rate but less frquently. What that does is that it brings fertilizer levels way up, and then they gradually decline and may run down to a lower than optimal level before refertilizing. This see-saw effect is not as good as the greater uniformity of a constant liquid feed program.

  Advantages and Disadvantages of Liquid Feed/Fertigation:
  

Advantages	Disadvantages
Uniform distribution.	Overhead irrigation may be inefficient.
Automation possible.	Proportioner equipment may be expensive.
Can be set up to meet the specific nutritional requirements for specific crops.

• Mixing the Fertilizer Solution

  Once you have weighed out the appropriate amount of fertilizer, add hot water (150 degrees F) to your fertilizer in a plastic, stainless steel, or fiberglass container used specifically for mixing fertilizer. Stir the solution until the fertilizer is dissolved. Then, pour the fertilizer solution into the stock tank. Dissolve any fertilizer residue remaining in the bucket with more hot water. When the fertilizer has been completely dissolved, fill the stock tank with water. Fertilizer stains, be careful. As always, read and follow the directions on the fertilizer bag.

• Fertilizer Concentrate Stock Tank

  When discussing liquid feed one of the terms we will be using is stock tank. When I mention stock tank, I am referring to the tank that holds the concentrated fertilizer solution. Optimally, concentrated fertilizer solutions should be stored in high density polyethylene containers, with secondary containment provided, in an area away from plant material. Stainless steel for stock tanks is another good choice. Keep in mind that you do not want a container that will deteriorate and contaminate your fertilizer solution. You also want to make sure that the tanks are relatively small - think "containment".

  One of the things that we must remind ourselves of is that we have a very concentrated fertilizer solution in this container . This is where trained personnel and containment come in to play. Be sure that the people working in the greenhouse understand how to mix fertilizers. Make sure you are trained properly so that when that fertilizer comes out the end of the hose it is at the proper rate and you're not going to run into problems with excess feed or deficiency because the amount of fertilizer was not mixed properly.

  For example, a mistake at this stage of the game, accidentally adding 2 grams of fertilizer from of the bag, instead of 1 gram, can have a serious impact on the growth of the plant material. Be sure you also check these proportioners on a regular basis to make sure they are in fact pumping the proper dilution ratio that you are looking and by keep your proportioners maintained as recommended by the manufacturer.

• Dilution/Injector Ratio

  The injector/dilution ratio or PPM (parts per million) compares the volumetric ratio of concentrated stock solution to the dilute fertilizer solution delivered to your crop. For example, a 1:100 injector will deliver 100 gallons of dilute fertilizer solution for each gallon of concentrated stock solution that is metered through the injector.

  With permission from the Ball Company, we have an example of how to determine parts per million (ppm) of an element in a fertilizer. Simply multiply the percent of the element by 75 and the answer will be the ppm of the element per oz./g. of the fertilizer in 100 gals./378 litres of water.

  For instance, how much 20-20-20 fertilizer should you use to get a 200 ppm nitrogen solution?

  Example: 0.20 x 75 = 15 ppm (% of nitrogen element in fertilizer multiplied by 75). 200 divided by 15 = 13.3 oz/377 g. (desired ppm solution divided by ppm per oz./g.).

  13.3 oz./377 g. of fertilizer are required to produce a 200 ppm nitrogen solution in 100 gals./378 litres of H2O.

• Fertilizer Application Rates

  Depend on:

  • Crop species
  • Growth stage
  • Time of year
  • Irrigation/fertigation systems
  • Watering schedule
  • Type of potting media

• Back Flow
  
• Safety

With fertilizers you should be aware of safety precautions. With these materials if you look at the bags of fertilizer that your getting you will see there are first aid precautions for example in case you get fertilizer in your eye. Flush the eye out, make sure you know where eye flush stations are located, make sure you have plenty of water there, make sure you flush them properly.

You should have MSDS (Material Safety Data Sheets) sheets for the fertilizers you are you are using located at the central Posting area of your greenhouse where you have most of your pesticides listed. Fertilizers are not any different than pesticides. Be aware of the fact that they may cause skin irritation if your skin is continually subjected to them. Certainly not in the same hazardous category as pesticides are, but one that we need to be aware of. Make sure you have the MSDS sheets at your central posting area at the greenhouse and so people can get recommendations off of them.

• Storage

  The fertilizer you see is stored in plastic containers each container is labeled both top and bottom so there is no confusion. A fertilizer storage area is dedicated to fertilizers. You can have small amounts stored in convenient locations, but your primary storage area should be dedicated specifically to the storage of fertilizers. Make sure you have the proper signage out so that people know that in fact fertilizer is being stored in this area. You want to make sure that you have proper ventilation in an area where you are storing fertilizers. Always make sure that you have good exhaust fans that keep not only the temperatures in the proper range but also supply a good air exchange.
  

• Proportioners/Injectors

In this section, we will be looking at different types of proportioners that are commonly used in both small and large greenhouses. The proportioners we will be looking at operate on either the Venturi principle. or a positive displacement pump mechanism. When we look at these proportioners we will referring to pictures that we have in the text.

We will be looking at one Venturi principle proportioner, the Hozon™ injector and two positive displacement pump type proportioners, the Dosatron Proportioner and Smith Measuremix Proportioner.

1. Hozon Injectors

The Hozon™ injector is an example of the Ventura principle of incorporating fertilizer into the water line. The Hozon™ injector works by creating a pressure difference between the fertilizer in your stock tank and the water flowing through the proportioner. This draws the fertilizer up into the water line, down into your hose, out and onto your plant material.

The Hozon™ has a fixed (nonadjustable) injection ratio of 1:16; one gallon of concentrate waters 60 sq. ft. The amount of suction is dependent on the flow of water and less is pulled when the water pressure is low. The Hozon™ siphons a concentrated solution from a stock tank filled with 16 times the recommended rate of the product for each gallon of water. As the water goes through a small opening it creates a suction that pulls fertilizer solution and mixes it with the water. Hozons™ are handy for small growers but are not very accurate because the dilution ratio with the Hozon™ injector may vary, depending on your water pressure. Consequently, you always want to check your water pressure so that you can calculate what your dilution ratio is. (insert how to do this) Otherwise, you can not be sure of how much fertilizer is getting on your plant material.

One of the things that we like to recommend when working with the Hozon™ injector is to put a pressure regulating valve in the line so that you know your water pressure is consistent from one watering to the next. A Hozon™ injector has a 1:16 injector ratio compared to a 1:100 injector ratio for the pump-type proportioners. This means that your stock tank has to be fairly large (less concentrated stock solution) for the 1:16 Hozon compared to the 1:100 positive displacement type proportioner. It is going to take 6 to 7 gallons of stock solution to put 100 gallons of water out the end of the hose (see fertilizer bag). A positive displacement type proportioner proportioner that has a 1 to 100 dilution ratio would only take 1 gallon of stock solution to put 100 gallons of water out the end of the hose.

There are a couple of things I would like to point out about the Hozon™ injector. One is the location where the hose attaches to the proportioner itself. There is a small internal bead that acts as a check valve keeping the fertilizer from being sucked back into the water line while the hose is not running. We want to make sure that this check valve is working. You can tell by removing the proportioner hose from the faucet - shake it a little bit and you will hear the bead rattling back and forth which means it is free and working. You can also tell if they're working by the sound of the water moving through them it has a very distinct sound when operating.

Theother consideration is the dip tube going down into the stock tank. It should have a small strainer at the end of it. You always want to be sure that this strainer is free and clear so that the fertilizer is not obstructed from moving up the tube. Another thing about these light weight dip tubes is that you want to make sure it is not floating in your stock tank. They are very light. At times they float to the top so you may want to put a small weight on it to be sure it is down in the bottom of your stock solution.

The Hozon™ injector is an excellent choice for homeowners and small greenhouse operators but may not be appropriate for commercial production of a greenhouse crop . It is relatively inexpensive and portable. They can be purchased at just about any garden store and cost between $15 and $20 a piece. As I look at this small piece of equipment, the Hozon™ injector, it's one that's used in greenhouses extensively, you can move it around from hose to hose and it's easy to operate.

2. Dosatron Proportioner

The Dosatron a positive displacement pump type of proportioner. This means that the pump is driven by the water that flows through the machine and that water pressure drives the internal pistons. In this system a specific amount of concentrated fertilizer stock solution is injected into the irrigation system to mix with a specific amount of irrigation water. There are many models based on flow rates and they have adjustable dilution ratios, 1:50 to greater than 1:200. The Dosatron proportioner is more expensive than the Hozon™ injector, but not as expensive as the Smith Proportioner, which we will consider next.

3. Smith MeasureMix Proportioner

Like the Dosatron, the Smith MeasureMix proportioner is a positive displacement pump. They are availble in dilution ratios of 1:100 to 1:8000.

This particular machine has a double head (header), giving it the capability of supplying two different fertilizer concentrated stock solutions that may be incompatible, in a single concentrated stock tank. Both concentrated stock solutions are pumped into a water line at the same time. The Smith MeasureMix proportioner has a crank shaft visible through a transparent plastic window. When the water is moving through the machine it turns the piston and proportions the fertilizer stock solutions into the water line. With a positive displacement pump like this, there is little variation in the dilution ratio.

There are two important things I would like to point out about the Smith MeasureMix proportioner. One, the water comes in on the bottom and goes out the top. When you have fertilizer in your line you will see it being pumped into the water line at the top of the machine. Two, their are two valves, one blue and one red on the side of the machine. The blue one is an on/off valve that allows you to turn your dip tube, to the concentrated stock solutions, off so that fertilizer is not drawn up into the pump heads. Make sure that this valve is turned on because if its moved in the other direction, the horizontal, it will be in the off position you won't be pulling any fertilizer up in your machine. The red valve is normally closed during operation. Turn it on when you want to back flush water into your dip tube to eliminated any air pockets.

This machine is a very reliable piece of equipment, it is also very heavy so you want to make sure you have it in a water line secure where it will be stabilized and in a position where it is not going to be moved around. There are situations where Smith Proportioners can be mounted on portable carts and moved through the greenhouse. A well constructed cart with good casters will do the job . Price wise, it is the most expensive of the three.

• Leaching

Regardless of the type of proportioner you use when applying fertilizer a general rule of thumb is to apply 10% excess water to your pot so that you get leaching of excess fertilizer solution out of the bottom of the container. If you don't apply enough water to get leaching, you're going to have salt build up from evaporation of the liquid fertilizers used and this can of course cause root injury to the plant material. A salt build up means poor root system development. A poor root system caused by salt build up means that when the plant dries out it may not get enough water.

• Is this consist with the Best Management Practices?

Greenhouse Best Management Practices (BMPs) are designed to reduce resource inputs and waste outputs in the greenhouse production process. The BMPs developed by the Cornell University Greenhouse BMP Task Force comprise three categories, Level 1, Level 2, and Level 3, all of which satisfy BMP principals and requirements. Leaching requirements depend at which BMP level you are operating. Level 1 assumes that little consideration is given to the amount of fertilizer applied and leaching is greater than 10%. Greenhouse growers operating at Level 2 attempt to limit the amount of leaching to 10% or less. Growers practicing Level 3 BMPs utilize ebb and flow benches in a conscious attempt to limit leaching to 10% or less.

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IV. How to Verify That Your Proportioner is Working Properly?

• Visual/Eyeball Method

There are two quick ways to determine if your machine is pumping fertilizer. First is the color coming out of the delivery hose. The fertilizer that goes into the stock tank has a dye in it, usually blue. The reason for this is that it allows you to see color coming out the end of the hose when you are fertigating your plants. Another way to tell is simply to check your stock tank. If your stock tank volume is continually going down you know that your machine is dispensing fertilizer.

These visual checks are ways to determine if your proportioner is at least pumping, but is it working accurately? Not necessarily. Just because it is pumping doesn't mean it's pumping at the 1:200 (or whatever) ratio you expect. Do an eyeball check, observing the environment and what happens to it, every time you walk by your stock tank. First, is the stock solution volume in the stock tank decreasing? Check daily and you'll soon know what to expect.

• Electrical Conductivity (EC) and pH

The most accurate way to check the dilution ratio is by performing an electrical conductivity (EC, ability of a substance to conduct an electrical signal) test on the fertilizer solution coming out of the end of the hose. Fertilizers are salts - chemical compounds that contain one positively charged ion (cation) bonded to one negatively charged ion (anion) that separate and dissolve in water. EC is also referred to as Total Dissolved Salts (TDS) or salinity (the amount of salts in a solution). All nutrients are salts, hence measuring EC is the same as measuring the total nutrients in a solution. The expected EC level for a particular combination of ppm N and proportioner dilution ratio is available on the fertilizer bag.

One way to check the EC is to use a pocket EC meter. An EC meter works by measuring the electric current between two electrodes (the electricity flows by ion transport). Electrical conductivity is higher in a nutrient-rich solution than a solution with less nutrients. PourThru Sampling is another way to measure the EC of a substrate. EC levels can also be monitored by the visual inspection of your crops. If the plants, in moist potting media, are not wilting and show no signs of leaf burn then the EC levels are probably correct.

The soil pH is a measure of the hydrogen ion activity. Soil at a 7 pH is neutral; if the pH is less than neutral, the soil is acidic; if it is greater than neutral, the soil is alkaline, or basic. pH affects the availability of elements to plants. pH is monitored in solutions and substrate by colorimetric tests and pH meters. Here is a chart from the University of Georgia Department of Agricultural and Environmental Sciences on the materials and rates necessary to lower the pH level of greenhouse potting substrate.

• Maintenance

  I would also recommend at this point to check the owner manuals that will accompany each machines. Whether it 's the Smith MeasureMix proportioner, the Hozon injector or the Dosatron check the owner's manuals and make sure you follow their maintenance instructions. On certain machines, you will have to replace parts such as "O rings" after a certain amount of use, this will ensure that your pump is working properly.

  I also recommend checking local codes and regulations to be sure that you meet all of the requirements for greenhouses when injecting fertilizers into water lines. You certainly want to be sure that there is no chance of fertilizers backing up into a system that contains drinking water.

Be sure you run a constant check on the proportioner to be sure it is working properly. On a regular basis:

• Check to make sure feed hose is above tank to prevent reverse flow into stock tank.
• Check solution color.
• Check EC of solution.

• Note: You sometimes see recommendations to use materials (insecticides, fungicides, algaecides) other than fertilizers with proportioners. I personally would not recommend using a proportioner for these. I stick strictly with fertilizers, or if you have a machine that you want to dedicate strictly for insecticides or fungicides or what have that may be ok. But a general rule of thumb would be to use these machines primarily for fertilizers and no other materials.

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IV. Other Forms of Fertilizing

• Preplant Application
  

  Dry fertilizers, not in liquid form, are normally mixed into the media before planting to ensure that the necessary nutrients are present. Examples of this are superphosphate, 10-10-10, and dolimate limestone (supplies magnesium). Trace elements are also incorporated into the media before planting. When introducing trace elements into the mix, use caution. Trace elements by definition are only needed in very small amounts so when mixing trace elements, especially in a small amount of potting media, mix the trace element with sand to assure uniform distribution in the media.
  
  

• Slow (Controlled) Release Fertilizers

Slow (Controlled) Release Fertilizers can be added as either a preplant or postplant application. One of the ways to acheive optimum plant growth is to combine a slow release fertilizer with your water soluble fertilizer. A good example of this would be a fertilization program of 200 ppm N and K with 14-14-14 Osmocote. One of the best crops of chrysanthymums we ever grew used this combination.

• Organic fertilizers
  • Examples: bone meal, manure
• Synthetics:
  • Example isobutylidene diurea (IBDU), a nitrogen source that releases slowly through hydrolysis (chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds).
• Resin and sulfur-coated synthetic organic and inorganic fertilizers
  • Examples of resin-coated fertilizers:
    Osmocote, Nutricote, Precise (many formulas of N-P-K Last 3 to 12 months)
  • Release Mechanism
    

  Water enters through pores in coat, fertilizer inside is dissolved, and fertilizer solution flows out.
  Rate depends thickness of plastic coat, pore size, number, pH, temperature, moisture, and bacterial activity.

Avantages and Disadvantages of Preplant Fertilizer Applications to Fertigation:

Adavantages	Disadvantages
Labor costs reduced	Fertilization control reduced
Nutrient runoff reduced	Cost
Preplant application	Media Testing Is Difficult

• Foliar Feeds

Do we ever use foliar feeds in the greenhouse?

Yes. The material which comes to mind in foliar feed is iron. Using chelated iron as a foliar application. There are also other materials you can put on with a foliar application: magnesium, *, *, and many different kinds of minor elements in particular applied on the foliage or sprayed on with a small hand sprayer. One of the advantages of doing this is that the material is available to the plant alot quicker by spraying it on through the foliage.

Be careful of the amount of material that you put on. Make sure that you check the recommended rates so that your not putting too much material on the foliage. Its not like putting it on the growing media, you have very little buffer compacity.

When you're applying this right to the plant material, I would suggest that you put it on small area first, give it a couple of days, see if there is any phytoxicity at all and then go ahead and make your application. Don't get too excited if it doesn't show up in a day or two.

Sometimes these things take longer; a watch pot never boils. Give it a few days and sometimes you forget about it and all of a sudden you look back and say it did help. Particularly if you are talking about iron, the old reliable. iron chlorosis in the leaves can be taken care of by spraying iron, 3 ounces to a 100 gallons of water. Check your Cornell Recommends.

Two other, magnesium and *, are adjusted by foliar applications. These foliar applications are usually based on foliar analysis of a particular area of your plant material, usually recently matured leaves. I look at the foliar analysis a little more honestly, it tells you what is in the plant not what is in the mix. This is another way in applying fertilizer, a good one, the caution is to check it first make sure there is no phytoxicity with material you are using and plant material you are using, what works on marigolds may not work on a petunia. You may get phytoxcity on one and not on the other
Check each one individually, before you make major applications with materials where you very rapidly spraying on alot of plant material.

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V. Summary

The information in this Web page is presented with the understanding that no discrimination or endorsment of any of the information linked to from this Web page is implied.

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