The type of equipment you use to apply fertilizer depends on a lot of things-the plant, how it’s planted, the weather-not to mention the type of fertilizer. For bareroot and container growers, the right choice can make the job a snap.
Fertilizer application equipment can apply chemicals in dry or liquid form. The appropriate equipment places the material at the desired rate in the desired location. In bareroot nurseries, fertilizer is usually applied dry in granulated pellets or coated form. In container production, nutrients may be applied in granular slow-release form or, more commonly, injected directly into the irrigation water supply, otherwise known as fertigation.
The application equipment you select will depend, of course, on your specific needs – and those of the plants you grow. And unless you grow only one species, you’ll need a variety of reliable methods. Offered here is an overview of the various types available and how each piece of equipment is best used.
Application equipment for dry chemicals
Drop-type fertilizer distributor
Tractor-mounted and trailer machines are available; hand-pushed distributors generally are used for small beds. Dry fertilizer is loaded into a hopper, which has a V-bottom with agitator and adjustable gates that control the rate of flow through the holes. Hopper widths are available from 2 to 12 feet and spread the fertilizer over the bed.
You may elect to incorporate fertilizer directly into growing media. For batch mixing, granular fertilizer can be dumped into the mixer along with other components before the medium is blended. For continuous mixing, a fertilizer dispenser meters the chemical onto the conveyor belt before components reach the mixing unit.
This is also called a spin or cyclone spreader. The fertilizer hopper can be trailer- or tractor-mounted, but hand-operated machines are also available. One or two spinning disks located below the hopper and powered by the tractor or a set of drive wheels distribute the fertilizer. Application rate is controlled by a slide gate. Ground coverage is greater than with the drop-type distributor, but uniformity is not as good.
This equipment can be fitted with fertilizer hoppers that apply chemicals at the same time seeding is done. Metering devices include the star wheel, feed roll, wire worm or auger. Drop tubes direct the fertilizer into the same furrow as the seed. Liquid fertilizer can also be injected into the soil.
Individual pot applicators
This drop-type applicator feeds small quantities into individual containers. The hopper holds a quantity of fertilizer that can be conveniently carried. A measuring device meters the chemical and drops it into the pot, and several thousand pots can be fed per hour.
Selecting an applicator
The size of the nursery and the type of plant being grown influence applicator selection. Even if your production covers hundreds of acres, a large machine may be too expensive to own and difficult to maneuver in small areas. On the other hand, a small machine may require frequent stops for refilling. No matter the size of your operation, consider the following when making your decision.
- Drop or broadcast spreaders take less power than drills. Stony soil is less of a problem.
- Placement of the fertilizer can affect the growth of the crop. Fertilizer placed on top of the soil may take time before it reaches the root system.
- Fertilizer applicators are heavy when full. Flotation tires may be a good investment, especially if the application is made when the soil is wet.
- If you already have a tractor, you may want to size the machine to fit it. Some manufacturers list horsepower requirements for their machines.
- Because fertilizers are corrosive, many modern applicators have stainless steel or plastic parts. Nevertheless, machines should be cleaned after each use.
- Ease of calibration is important if you want accurate application, and especially to avoid the cost and possible adverse effects of overfertilization. It should be done with each change of fertilizer material. Follow the instruction manual to make the correct adjustments; rates of fertilization may differ from application to application, so be sure to consult the product’s label each time.
Fertigation is the controlled feeding of nutrients to plants through the irrigation system. Application of fertilizer through the water system has several advantages:
- Easy adjustment of nutrients, depending on crop needs.
- Nutrients become available to the plants quicker.
- More accurate placement of fertilizer.
- Less fertilizer needed.
- Reduced labor to apply fertilizer.
- Irrigation can be done with many systems; four are described here.
Lateral supply lines feed sprinklers that produce a circular pattern for outdoor plants in the nursery or for seedlings growing in a greenhouse. To be effective, a pattern of at least 60 percent overlap is needed to achieve uniform coverage.
Equipment for applying irrigation water with a boom that travels over the growing area is available for both outdoor and greenhouse production. This system is the best method for watering plug and cell trays, as very uniform application can be made. Both hand-operated and motorized, computer-controlled booms are available.
Improvements in drippers have made this system viable for beds and larger containers, which result in considerable savings in water and nutrients. Clean water is required. Pressure compensating drippers are required for sloping beds to receive uniform distribution. High-output drippers are now available; these help you achieve quicker application of water with less clogging.
Mats, trays, benches and flooded floors are systems where the nutrient solution is absorbed by the growing media from underneath the container. Used in the greenhouse or on limited outdoor production areas, these systems work best with small containers and plug trays.
Venturi suction device
The simplest low-cost devices use the Venturi principle to create a pressure differential between the container holding the fertilizer solution and the water line. As water passes through the restricted area of the injector, the velocity is increased, creating a vacuum. A small tube connected at this point allows the fertilizer concentrate solution to be siphoned into the water stream and mixed before reaching the plants. The fixed-dilution ratio will vary somewhat with water pressure differences and hose length.
These units use a pressurized tank attached to the irrigation line in two places. A control valve achieves a pressure differential between the inlet and outlet. Inside the tank, a plastic bag (the bladder) holds the fertilizer solution. Water from the supply line surrounds the bag, forcing the solution through a metering valve into the water supply. The bladder improves the uniformity of discharge. The rate of fertilizer injection can be regulated to some degree by varying the pressure. There are no moving parts, and the bag can be replaced easily.
Water motor controlled injector
Water motor-driven proportioning injectors use water flow to operate a piston or diaphragm to inject or force fertilizer into the water stream by positive displacement. As water flows through the injector, the water causes a cam to turn and push a piston back and forth. This equipment gives consistent feeding ratios at specific flow rates over a wide range of pressures. Water motor injectors usually decrease line pressure more than water meter styles.
Water meter controlled injector
These injectors use a water meter mechanism to determine flow rate and a water- or electric-powered diaphragm pump to inject the fertilizer. They can be purchased with several heads attached to the same motor so that more than one nutrient can be fed at the same time.
Selecting an injector
All types of injectors can be successfully incorporated into a greenhouse or outdoor irrigation system. The following factors should be considered when making a selection. Some of these may seem intuitive, but with all the decisions you must make each day, it’s good to have a handy check list available.
- The injector must be compatible with the water flow rate in gallons per minute. Most injectors have a range of flow over which they will operate. Select one that will allow for some expansion should a different irrigation system be installed, but don’t oversize it, as larger injectors may not work when only one hose is turned on.
- Except for the Venturi type, all injectors have variable dilution ratios. This is desirable, as available concentrations or the size of the mixing tank may require different ratios. Check on the ease of changing the ratio.
- Injectors with an integral mixing tank are available in several sizes. A separate concentrate supply is needed for most injectors. A 5-gallon pail is adequate for one hoophouse. Larger plastic or concrete tanks can also be used. Select a tank large enough to feed a single greenhouse or several zones to reduce frequency of refilling. In larger ranges, nutrient concentrate may be distributed from a central tank throughout the range in PVC pipe. Agitation within the tank is important to maintain a uniform solution.
- Fixed units are used in small operations or where all irrigation water is piped to the greenhouses. Portable units can be moved from one area to another.
- Multiple injector units are required where more than one chemical is applied at the same time. They are also used where individual nutrient levels are monitored by a computer.
- Check the specifications for the amount of pressure loss caused by the injector. Some units lose as much as 15 psi. For some water systems, this may limit the amount of hoses or number of zones that can be operated at one time. Also, be sure that piping is large enough to keep pressure loss to a minimum.
- For large operations, an injector that can be integrated into the computer system is desirable. Sensors, pumps and water meter should be compatible with the software.
- Check to see if the injector is compatible with the chemicals that you will be applying. Water should also be clean to avoid wear. Most manufacturers recommend that a 200-mesh filter be inserted before the injector.
- Safety devices should be installed in the system to prevent backflow into the water source. A backflow preventer is required on all systems connected to potable water. A check valve should be installed in the chemical injection supply line. An interlock should be installed to prevent an electrical injector pump from operating if the water flow stops. Repair parts and dependable service should be available locally.
- Injector operation must be checked frequently and calibrated to ensure proper operation and application rate. Follow the manufacturer’s recommendations for calibration.
John W. Bartok Jr. is an agricultural engineer and extension professor emeritus of the University of Connecticut. He has written a number of books, bulletins and articles on greenhouse and nursery technology, and is a USDA Certified Technical Service Provider who conducts energy audits in New England. Two of his books, Energy Conservation of Commercial Greenhouses (NRAES-3) and Greenhouse Engineering (NRAES), are available from Cornell Cooperative Extension and online at www.NRAES.org. He can be reached at firstname.lastname@example.org.