Tuesday, November 17, 2020

Understanding Physical and Chemical Characteristics of Substrates

Understanding the characteristics of substrates often informs the design and functionality of growing media. There are two main characteristics to focus on when it comes to substrates - physical characteristics and chemical characteristics. Physical characteristics include the soil texture, particle size distribution, and porosity. There are characteristics that cannot be changed. Chemical characteristics of substrates include potential of hydrogen (pH), and electrical conductivity (EC). The chemical characteristics are quite dynamic and are easy to change- whether naturally or through means of the grower. 

Physical Characteristics:

 

Once the percent of sand, silt, and clay of a soil has been determined, you can classify the texture of the soil. This can be done using the soil texture triangle. It is very simple to use- all it entails is taking the percentages of sand, silt, and clay, and then lining them up appropriately on the triangle. For example, if a mineralized soil contains 65% sand, 20% silt, and 15% clay, this soil will be classified as a Sandy Loam. It should be noted that this only works with mineralized soils. In most horticultural applications, growers tend to use what is referred to as “soilless media”, meaning  the growing media lacks mineralized top soil. This particular type of growing media is made with other naturally occurring substrates, such as pine bark, Canadian sphagnum peat moss, sand, expanded clay aggregate, etc. 


Whether a grower is using soil media or soilless media, particle size distribution is perhaps the most important physical characteristic of substrates and growing media. Particle size distribution is the measurement of the gradation of specific sized particles, ranging from largest to smallest. For example, we know that ½” pine bark is larger in size, therefore we expect a higher amount of large aggregates in the overall particle size distribution of the substrates; whereas Canadian sphagnum peat moss is smaller in size, resulting in particle size distribution on the smaller size. The size of these substrates will influence the functionality of growing media, which in turn will affect the growth and overall health of crops. Particle size distribution of substrates and growing media is crucial because it directly impacts porosity. When dealing with particle size distribution and porosity, it is crucial to find the perfect ratio of large particles to small particles.

 

Porosity is representative of the amount of pore space within a given volume. If you have substrates that are large in size you will have larger spaces, which results in high porosity; inversely, if you have substrates that are smaller, you will have smaller spaces, which results in low porosity. Once the media is established in containers or the landscape, these pores fill with either air or water. Finding in the happy medium between high porosity and low porosity is crucial for plant health.

 

If you have a growing media that has too large of particles or too high of porosity, it will complicate air and water exchange. The excess of large pores allows for intense drainage, which will affect the moisture retention of the crop. If there is not enough small pores present, water will not be able to fill in any of these pore spaces, ultimately resulting in loss of moisture retention. Additionally, if there are too many large pores present, it will affect the crop’s ability to root; making it more challenging for the crop to anchor on to anything substantial. On the other end, if the growing media has too low of porosity, or too many small pores, this too will complicate air and water exchange in the growing media profile. If the pore spaces are too small, they will be too compact. The compaction of the growing media will result in improper drainage, leaving the crops water logged. Compaction will also complicate air exchange in the growing profile. Without enough air exchange, roots will become “choked off”. Too little of porosity can lead to necrosis for the crops. 

 

Chemical Characteristics:

 

Potential of Hydrogen (pH) is the measurement of how acidic (1-6), neutral (7), of alkaline (8-14) a solution is. Different substrates used in the horticulture industry have varying pH measurements. For instance, typically pine and  Canadian sphagnum peat moss have lower, more acidic pHs, whereas sand and composts typically have higher, more alkaline pHs. When dealing with overall plant health, pH is the most important, and often most overlooked chemical characteristic. If the pH of the growing media is not in the ideal range for the crops being grown, the crops may start to show signs and symptoms of distress. This is because certain nutrients are only able to be absorbed at very specific pH ranges; usually between 6.0-7.5.  If plants are showing any symptoms of distress, it is best to check pH fi as the first step in a successful plant management strategy. If you’d like more information on how pH and plant health are related, please check out the blog post pertaining to pH.

 


Electrical Conductivity (EC) is the measurement of soluable in a solution, such as fertilizers. EC is related to the fertility of crops and is often a good way to gauge a fertilizer regiment for plant health management. EC levels will vary depending on the crops being grown- but have no fear, EC can, and will often change. It is important to understand what the ideal EC range is for your crops- if the EC levels are too low, it may affect the nutritional value of the crops; whereas if the salt levels in crops are too high, they will ultimately “choke” out the plant, leading to death.  If EC level are too low, fertilizer may be added to the crops to create the targeted EC range; whereas if the EC levels are too high, leaching can be done. It is important that growers not only understand their EC levels, but regularly monitor them throughout growing cycles.

 

By understanding the physical and chemical characteristics of substrates and growing media, growers are able to make more informed decisions. This knowledge can assure any and all growers that their growing operations and their corps are a sure success! If you have any more question or would like more information on physical and chemical characteristics, please feel free to contact us! 


- Alexis



Picture Sources:


Van Es, Harold. “Soil Health Manual Series.” Cornell University, Dec. 2016, cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/f/5772/files/2016/12/04_CASH_SH_Series_Texture_Fact_Sheet_121916-1obbt8q.pdf.

Friedl, Sarah. “Permeability & Porosity: Definition & Impacts on Soil & Rocks.” Study.com, 2020, study.com/academy/lesson/permeability-porosity-definition-impact-on-soil-rocks.html.

P., & N. (2015, October 18). Acids, Alkalis, and the pH Scale. Retrieved November, 2020, from https://www.compoundchem.com/2015/07/09/ph-scale/

  

 

Mycorrhizae: The Most Helpful Fungus Around!

Mycorrhizae is a beneficial fungus that creates a symbiotic (or mutually beneficial) relationship with the root systems of plants. So how does it work? Mycorrhizae colonizes in the root zone of the plant. From there, the mycorrhizae will form what is referred to as “mycelium”. The mycelium is essentially a colonization of long, white, fibrous filaments that function as a secondary, extended root system for the plant. The mycelium grows outwards in all directions, increasing the overall surface area of the root zone. Essentially, the mycorrhizae acts as an extension of the root system and aides in the absorption of water and nutrient. especially during times of high environmental stress; such as droughts. The beauty of mycorrhizae is that it's a naturally occurring fungus that is essentially an insurance package for your plants! 

Left: Soil containing mycorrhizae- The web-like appearance seen is mycelium. Vs. Right: Soil that does not contain mycorrhizae.


Believe it or not, but certain crops require certain types of Mycorrhizae. Studies have found that certain crops are better at utilizing one kind of mycorrhizae over another. By choosing the correct type of mycorrhizae, your crop will be able to utilize the mycorrhizae to the best of its ability, ultimately creating stronger, beneficial relationships with one type of mycorrhizae versus another. There are various types of Mycorrhizae but I would like to discuss the two most common types; Endomycorrhizal (Endo) and Ectomycorrhizal (Ecto). The Endomycorrhizae and the Ectomycorrhizae have the same basic functionality, but differ in two major ways. The first way in which they differ is based on what crops they are compatible with. 
The second way in which the Endomycorhizzae and Ectomycorrhizae differ is in how they interact with crop's root systems. 

The Endomycorrhizae is the most commonly used type of mycorrhizae. This is because endomycorrhizae forms relationships with approximately 90% of plant species. Endomycorrhizae works by “penetrating into the root cortex and forming nutrient exchange structures within the root cells”.  Endomycorrhizae is commonly used for most leafy and/or fruiting bodies. 

Endomycorrhizae

In comparison, the Ectomycorrhizae forms relationships with approximately 10% of plant species, mainly hardwoods and conifers. Ectomycorrhizae differs quite drastically in its relationship to the root system, meaning it “does not penetrate into the root cell walls, but forms a sheath around the root”. Although the structuring of the mycorrhizae differs, the functionality is still there! 

Ectomycorrhizae

No matter what crop you grow, there is a mycorrhizae out there for you! This fungus is not only interesting, but it is hard working! Due to the nature of the symbiotic (mutually beneficial) relationship it forms with plants, the mycorrhizae cannot live unless your plant lives; in other words, it is the mycorrhizae’s job to keep your plant alive, so in turn, the mycorrhizae can survive. Whether your plant is facing environmental stress such as drought or nutritional stress, such as increased salt levels, mycorhizzae will work to protect not only your plant, but your livelihood as a grower! I encourage you to research more about mycorrhizae and further educate yourself on just how cool this fungus really is!

- Alexis


Picture Sources:

VanSomeren, Lindsay. “How Do Mycorrhizae Work? Explained Simply.” Untamed Science, July 2016, untamedscience.com/biology/ecology/mycorrhizae/.

“WHAT ARE MYCORRHIZAE?” All about Mycorrhizae, Its Benefits, Application and Research and Development, www.mykepro.com/mycorrhizae-benefits-application-and-research.aspx.

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