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Introduction to Media :

When it comes to growing media, especially with regards to Citrus Nurseries, two important aspects are to be considered. These are the media’s physical and chemical properties.

With regards to physical properties five characteristics need to be given attention: 1. Structure 2. Particles’ size and shape 3. Water holding capacity 4. Air filled porosity 5. Readily available water (RAW). The three most important characteristics when it comes to chemical properties are pH, Electro Conductivity (EC), and the Cation Exchange Capacity (CEC).

The physical properties of a media type are important because they help achieve desired root distribution and density. The structure of the media is just the general look of the media whether it is more calcareous, clay like, sand like, or loam like. Based on the media’s structure one can assume certain qualities with relation to the particle size and shape. For example in a more clay like media you would normally assume that the particle size would be bigger and the shape more malleable as opposed to say a more sand like media where the particle size would be significantly smaller and the structure more defined and less flexible. The particle size and shape are important because they then play a determinant role in defining the next three physical characteristics of the soil that of water holding capacity, air filled porosity, and RAW. The water holding capacity basically just means the ability of that particular media type to hold a certain amount of water per specified time. Of course, the emphasis is placed on both the amount of water and the time. The same gaps in the soil structure that allow for the water to seep through them also allow air to pass through when water is not available. Therefore the air filled porosity has a direct relationship to the water holding capacity. Now, the air filled porosity is measured by percentages and different plants require different amounts. When it comes to citrus tree production the best measured air filled porosity falls between 14-20%. Those two aspects combined have a direct relationship to the RAW in the particular type of media. RAW is significant in that it measures the real water retention capacity of a particular media type. Besides the physical properties, there are the three major chemical properties to any media type: pH, EC, and CEC. Each one of these properties is measured by a number particular to its own purpose. A pH measurement is important to determine the optimum level at which the root system of a particular nursery plant will be most active and different nutrients are available; therefore the time where nutrient absorption is at its highest. The best pH for citrus nursery plants lies in a range of 5.8-6.2. The EC on the other hand is a measurement used to gauge the salinity of a medium. Of course, the more saline the medium the worse the nutrient absorption rate. Good results have been achieved in nursery citrus plants with EC values within the range of 0.8 – 1.2 after enriching medium with fertilizers. The last chemical property of importance to us is the CEC. The CEC is a measurement used to determine the amount of positively charged particles in the media type susceptible to clinging on other negatively charged particles which may come from the nutrients being used in the irrigation, fertigation, or other chemicals used. This is important because based on the media type, there is a need to determine the right chemical composition of products used whether through irrigation water, fertilizer, or other chemicals use, and their impact on the CEC of the medium.

All in all what we can understand from this whole section is that there are two important aspects when it comes to media and that is its Physical and Chemical Properties. The physical properties as we have seen have an effect on the rooting system of the plant particularly. The chemical properties have more to do with nutrients and their absorption through the root system. Therefore it is essential for any nurseryman to utilize these two aspects and master them in order to achieve success in his final product producing his perfect tree.
Various Types of Media and Mixing >>