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Soil textures and ions

Updated: Aug 9, 2019

While Soil Orders reflect the age and mineral composition (or lack of minerals) of the soil, soil textures focus on the particle size. Particle size makes all the difference when it comes to water and nutrient retention in your soil!



There are three main textures of soil particles: the biggest is sand, next is silt, and the smallest particle is clay. Soil tends to be any variety of mixture of these three depending on where you live. Obviously, if you are in the Arabian desert your soil will be a 90+ percentage of sand. If you are on the bottom of a lake, it is likely the soil on the lake bed is silt. The best kind of soil actually, is an un-equal ratio mixture of the three, called loam. Loam is the perfect combination because it allows for water retention, pores for soil breathing, and a capacity to hold on to nutrients. There are sandy loams, clay loams, silty loams, clay-silty loams, etc. The best of the best though is good ole’ pure Loam. For more information you can simply look up the triangle of soil textures on the web, or see our references page. You’ll find a figure that gives the percentages of particles and what soil texture they make up based on the ratio of these three particles. Knowing your soil texture, is an important step to helping your plants.


What are some qualities about the soil particles individually? Typically sand is very porous (good for breathing) but terrible with water retention. Because the particle size is so large, sand also has a hard time holding on to nutrients which can easily be leached or in other words, washed out. On the opposite end, Clay with its tiny particle size is extremely good at holding both nutrients and water but does not necessarily have the best breathing potential. The small particle size allows for ions (a word which simply refers to any atom or molecule with a charge) to interact with the clay particles. Positively charged ions (called cations) and negatively charged ions (called anions) are constantly interacting in the soil. For example, the nutrient Magnesium has a positive charge and will interact with negatively charged clay particles. When a soil has the ability to interact with positively charged nutrients this is referred to as its “Cation exchange capacity” or CEC. The higher it’s CEC typically means the soil has a high potential to hold on to positively charged nutrients that plants can eat like Mg, Ca, Ammonia, etc. This creates highly dynamic soil chemistry. Conversely it can also hold on to pollutant cations like lead. Therefore, just because you have high clay content, doesn’t mean your soil is immune!


Because clay typically increases a soil’s Cation exchange capacity you do want a good amount of it, but too much clay can be ineffective. Why? Again, clay’s particle size is very small, thus disallowing a lot of breathing, while retaining lots of water. If there is too much water in clay soils, it can take a long time to drain, and can drown your plants or worse, allow mold to grow. Clays also have a high expansion and shrinkage potential. For example, as mentioned about “Vertisols” in our last episode, places with high clay content can expand and flood the ground when wet, and create giant cracks when dry as the soil shrinks.


Unfortunately, not everyone is blessed with Loamy soil. However, there are a couple of things you can do to help out your soils. Although a number of things have helped like field aerators, growth blankets, seasonal watering schedules, etc, the best way to help with the inefficiency or over compensation, is to put microbes in your soil. They can help retain moist environments while still allowing the soil to breathe. No matter the composition of your soil, microbes will cater to what it needs, naturally because they are interacting in real time.


Meristems—the reason your grass keeps growing but never flowers.


Have you ever wondered why turf grass grows but never makes flowers? Or how it is able to keep growing even when you have cut it over and over again? It all comes down to a single word, “Meristem”


What is a meristem? It is a small group of “undifferentiated cells” which simply means they haven’t yet received a responsibility of the type of cell they will become. For example, you have eye ball cells, skin cells, liver cells, and heart cells. Plants have root cells, leaf cells, flower cells, etc. So meristematic cells just haven’t become a “type” of cell yet.


So, what do they do? Much like stem cells in humans, their primary role is to divide and then they have the potential to become any kind of cell. In plants, these cells are only found in a few places, and usually at an apex or “peak” and thus their name is determined by their location. For example, a root apical meristem is where un-dividing cells grow and elongate in the roots. A stem apical meristem creates leaves on the stem, and a floral apical meristem, is what allows flowers to grow near the top or ends of plants. An artichoke is a good example of an apical meristem. The leaves seem to continue to grow in a circle forever and ever inside—unless…. you stop and pull those leaves off one by one. What do you find at the center? A tiny mound of cells you’d be lucky to see with the naked eye! This mound is what continually makes all those leaves, which in turn grow to be big and strong. That mound—is a meristem. Meristematic cells divide and make more cells which eventually become differentiated, or in other words cell “types”.


You can pull the leaves off of any plant, and it will be the same—an almost seemingly endless cutting away of leaves that just gets smaller and smaller. In another sense you can even call meristems a type of motherboard for plant function because they communicate where the leaf will grow, or what the surrounding undifferentiated cells will become. So how does this fit into the bigger picture of plant growth?


When a seed is planted there are two meristems that start to work right away: Root apical meristems and stem apical meristems. As the plant is still in its “baby” stages it focuses just on getting nutrition, sunlight, good water, and growing bigger. In a sense, the plant needs to test its surroundings and has a limited time to do so—if it’s a healthy environment, or if it needs time to collect the resources it needs to start producing flowers and seeds the plant works until it is ready. When the time comes, a transition will help, much like adolescent teenagers, and the stem will shoot up. This is also called “bolting”. As soon as the stem has bolted, the leaves will start to get harder/less soft, and the plant will focus all of its energy on producing flowers and seeds. It has reached its reproductive stage.


So why does sports turf never flower? Why do floral meristems never form? How is it that grass can just keep growing?


Well it turns out that a plant meristem never stops growing until a transition happens, or its killed. If the transition from growth to flowers doesn’t occur, then the plant will continue to grow leaves. This is how your grass keeps growing, and why it never flowers. When it is cut, it's like getting a haircut, but because it hasn’t had time to bolt to its flowering reproductive stage, it will go back to simply growing leaves. Want to hear a fun fact? When you allow your grass it bolt, it will grow flowers. Those flowers will grow seeds, and that is how most grains are formed. Corn, wheat, rye, barley, rice? —All grasses. You probably don’t want your beautiful turf to look like weeds though, so we recommend keeping it on a mowing schedule.


#soil #particlesize #minerals #meristems


References:

https://archive.lib.msu.edu/tic/stnew/article/1991sep4.pdf

https://www.qld.gov.au/environment/land/management/soil/soil-properties/texture

http://geo.msu.edu/extra/geogmich/soils.html

https://en.wikipedia.org/wiki/Loam

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447039&topicorder=2&maxto=10

https://www.ctahr.hawaii.edu/mauisoil/a_factor_ts.aspx

http://www.soilquality.org.au/factsheets/cation-exchange-capacity

http://nmsp.cals.cornell.edu/publications/factsheets/factsheet22.pdf

https://www.canr.msu.edu/news/what_is_your_soil_cation_exchange_capacity

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