How to Maximize Fertigation in Greenhouse Pepper Production

bins of greenhouse bell peppers

Demand-driven fertilization in pepper production balances the fertilizer supplied with crop demand for maximize yield and efficiency of resources.

Peppers are a central crop in controlled environment production. In good conditions, they can yield 10 to 20 times more than corresponding outdoor production.

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A method relevant for such crop production is demand-driven fertilization (DDF). The foundation for DDF was developed in Sweden a couple of decades ago. The discoveries of the principles behind the concept was awarded with the Wallenberg Prize, which, for all intents and purposes is a Nobel Prize in biology. It all began with the ingenious researcher Professor Torsten Ingestad. He had an intuitive way of understanding plants and plant nutrition, and he always used a no-nonsense approach, in the simplest way possible. In short, his core discovery was that balancing mineral addition with the internal nutrient need of the crop results in maximum production and minimum adverse environmental impact.

Today, these discoveries have been condensed into a plant nutrition method that has helped transform fertilizer management in virtually all niches of plant production.

Balance Optimal Nutrient Ratios With Crop Demand
Pepper production is the perfect example of how the concept of demand-driven fertilization can be implemented in a simple manner.

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The method can be divided into two main parts:

(1) Supply all essential plant nutrients in optimal ratios. Meaning, providing the nutrients in the ratios found in pepper at maximum growth rate. One of the surprising aspects of this was the researchers found that most plants need the nutrients in very similar ratios.

(2) Deliver the nutrients over time in sync with the demand of the crop. In the first part of the season, a pepper grows virtually exponentially, which means the biomass of the crop increases with a certain percentage each day. This indicates that the daily demand for the nutrients also increases with the same percentage. The supply should match this pattern as much as possible for optimal results.

The ratios between the nutrients are more important than what most people know, because when they’re in balance they allow for maximum growth, while simultaneously using fertilizers in the most efficient way possible. In the table at the bottom of this article, you see the ideal balance for most crops and an explanation on how to apply it for pepper production.

Nitrogen Matters

A second important feature is that nitrogen will function as the limiting nutrient. Note that I’m not referring to deficiency, only the limiting factor. This means that through the supply of the nutrients nitrogen will function as a gas or brake pedal of the growth rate, depending on what you want to achieve with production.

The last point regarding the ratios is the importance of supplying all the essential nutrients correctly throughout the entire lifecycle of the crop. Most growers of controlled environment today are aware that all the nutrients are important. Still, the emphasis on accurate supply can often be missing. Besides having accurate ratios, all the way down to the least-needed nutrient, availability of plant nutrients to the crop is a common issue, and a big issue, when optimizing production efficiency. All the nutrients are equally important all the time. Therefore, it’s recommended to use products with chelated micronutrients.

Keep Application Straightforward
Then it comes down to the application rate. Here some growers and experts take an approach that either lacks enough precision or is over-complicated by an unnecessarily sophisticated system that includes different fertilizer products, mixing tanks, and application technology.

DDF takes the most intuitive and efficient approach. According to DDF, all the nutrients are applied all the time throughout the crop’s lifecycle at the same rate the crop grows. This entails a relative addition rate; peppers initially grow rapidly, and then at the peak of the season their growth rate slows down due to self-shading, genetics, and other factors. In simple terms, this means the crop increases its biomass with a certain percentage each day. Consequently, the fertilizer dose should increase each day with the same dose. When growth slows down, so should the fertilizer application.

Here’s How to Apply DDF to Your Production
One high-level way to implement this principle is to use one single, but complete, fertilizer containing all the essential nutrients in accurate ratios. Establish the initial nutrient content when your plants are small as your next step. Finally, determine the maximum growth rate and create a program that adds the correct dose daily. How the dose is spread over each day is less important and can be adjusted according to the limitations of the system.

A simpler version is to allow the water uptake to be the controlling factor for the nutrient uptake by simply adding a constant concentration (based on the same complete fertilizer) that matches the growth rate of peppers in the given conditions (i.e., light levels and temperature). Although this approach is simpler, take caution with regard to evapotranspiration from the growing media. If those losses are significant due to air humidity level and large open surface areas, they need to be accounted for when setting the concentration of the nutrient solution.

Another key parameter to be aware of is the possibility of nutrient accumulation in the growing media. If the method is implemented with high precision, this shouldn’t be a problem, but to be on the safe side, it’s wise to have a small draining fraction.

Nutrient Ratios

The table below illustrates the proportions of nutrients needed at maximum growth for most crops. The ratios are expressed in percentage of nitrogen. Note that certain proportions are expressed in intervals. These differences are, in part, due to differences in species, but particularly to which parts of the plants that are harvested. For pepper production, it’s important to stay in the upper end of the spectrum, especially for potassium (K), as the fruit bell will accumulate that nutrient.

The stated ammonium/nitrate ratio is a default position recommendable for most systems. However, adjustment can be necessary.

It should also be pointed out that the micronutrients should be chelated when applied on the levels presented in this table, as a portion of them otherwise are at risk of becoming unavailable for the plants in soil/media interactions, thus compromising accurate balance and sufficient supply.

Nutrient table for greenhouse peppers

*Exact ratio for nickel (Ni) is unknown. However, it’s known that it is very small.

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