Plants need certain nutrients to live, grow, and reproduce. These nutrients are divided into macronutrients and micronutrients. When a nutrient is missing, plants respond by characteristic visual symptoms. The ability to recognize these symptoms is essential in determining how and when to fertilize. Fertilization is the addition of nutrients to the media or the plant.
Nutrient deficiencies and toxicities depend largely upon the presence and availability of the nutrient. The pH of the media determines the availability of the nutrient to the plant—whether its soluble or not. For example, in cases of extreme pH ranges, some micronutrients are unavailable, while others are available in toxic quantities.
In general, fertilizer labels give the same information as pesticide labels with the addition of the fertilizer analysis. Other information found on the fertilizer label is what the fertilizer is derived from and the amount of various nutrient compounds available in addition to NPK, as well as the dilution ratio.
II. Fertilizer Application
A general rule of thumb when applying fertilizer is to apply 10% excess water so that leaching of excess fertilizer solution occurs. Without leaching, salt build will occur, which can cause root injury to plants. Best Managment Practices must be followed at all times.
1. Fertilizer Application Depends on:2. Ways to Apply Fertilizer:
- Type of fertilizer
1. Hozon Injectors
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.
2. Dosatron Proportioner
The Dosatron proportioner is driven by water that flows through the machine and 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.
3. Smith MeasureMix Proportioner
Like the Dosatron, the Smith MeasureMix proportioner is a positive displacement pump. 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.
John Kumpf on Proportioners—
"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. A general rule of thumb would be to use these machines primarily for fertilizers and no other materials."
Always follow the manufacturer's directions found on the fertilizer bag. Mixing should be done in a plastic, stainless steel, or fiberglass container used specifically for mixing fertilizer before adding to the stock tank. The greenhouse manager must know how to determine parts per million (PPM) in order to create the proper fertilizer solution.
IV. Types of Fertilizing
There are different types of fertilizers used in the greenhouse. As with anything else, the manager must become acquainted with the various types and their uses.
There are many more types and applications of greenhouse fertilizers that are not covered in this unit.
Always check the owner's manual of the equipment being used. It is also helpful to check local codes and regulations/requirements. Be sure you run a constant check on the proportioner to be sure it is working properly.