Soil Is Interesting

                I finished my Master Gardener class and learned something new from every lecture.  The class I found most interesting was the lecture on soils – what they are made of, what is in them, how we can work with them, etc.

                Are you aware that soil is made up of weathered rock fragments, organic matter and living organisms?  There are components that are living and some that are not living.  Minerals and dead organic matter make up one portion, and microorganisms, invertebrates, and plant roots make up the living part.  “Soil provides nutrients, water and physical support for plants and air for plant roots.”

                The temperature of the soil has a huge impact on “seed germination, root growth, microbial activity, and nutrient availability and uptake.”  Soil in Alaska is cold and must be warmed to garden successfully.  Many Alaskan gardeners use raised beds in order to garden successfully; others use black plastic or other covering to warm the soil.

                For successful gardening soil must “be both permeable to water and able to supply water to plants.  These two characteristics depend on the network of pores in the soil.  Large pores are made by insects, earthworms, and roots and allow water to rapidly drain with gravity.  Small pores are responsible for increasing the soil’s capacity to hold water against the force of gravity.  Plants need sufficient water but not too much water.

                Whether or not soil has large or small pores depends on its “texture, structure, compaction, organic matter and living organisms” in it.  Texture describes when the soil is more fine or coarse, and this depends on the mixture of sand, silt, clay in the soil. You can tell the quality of the soil by the feel of it.  Sand feels gritty, silt feels smooth like flour, and clay feels hard when dry but can be molded easily when moist.  The difference is made by the size of the individual particles.  Sand particles are the largest; silt particles are smaller than sand, and clay particles are the smallest.  “Although all of these particles seem small, the relative difference in their size is quite large.  If a typical clay particle were the size of a penny, a sand particle would be as large as a house.”  A good garden soil crumbles in your hand when it is ready for tilling.

                “Nearly all soils contain a mixture of particle sizes, giving them a pore network containing a mixture of pore sizes….  A soil with roughly equal influence form sand, silt and clay particles is called a loam.  Loams usually make good agricultural and garden soils because they have a balance of macropores and micropores.  They usually have good water- and nutrient-holding capacity, along with moderate permeability.”

                Sandy loams are similar to loams but will drain water more quickly.  Silt loams will hold more water.  Clays and clay-loams are hard when dry and sticky when wet; they have the greatest capacity to hold water and nutrients.  “Almost any texture of soil can be suitable for gardening, as long as you are aware of the soil’s limitations and adjust your management to compensate….  Many soils can benefit from additions of high-quality organic matter….”

                Besides the texture of soil a gardener needs to be aware of the slope, the aspect (direction of exposure), and the depth of the soil.  Slope determines the availability of water because water flows down with gravity; there is usually more water in a valley than on the mountain ridge.  “Site aspect also is important.  South- ad southwest-facing exposures collect the most heat and use the most water.”  Depth is important because deeper soil holds more water than shallow soil.

                Soil is alive.  “Besides the plant roots, insects and earthworms you can see, soil is home to an abundant and diverse population of microorganisms.  A single gram of topsoil (about ¼ teaspoon) can contain as many as a billion microorganisms.”  Most of the microorganisms are located in the soil surrounding the roots of the plants – an area known as the rhizosphere.  The organisms break down plant remains and other organisms and make energy, nutrients, and carbon dioxide available to the plants.  This also helps to stabilize the soil more.

                Soil supplies 17 essential plant nutrients.  There are macronutrients and micronutrients.  The primary nutrients are nitrogen (N), phosphorus (P), and potassium (K).  Secondary nutrients are sulfur (S), magnesium (Mg), and calcium (Ca), carbon (C), hydrogen (H),

oxygen (O), and nickel (Ni).  Micronutrients are zinc (Zn), boron (B), iron (FE), manganese (Mn), copper (Cu), molybdenum (Mo), and

chlorine (Cl).  If the soil is deficient in any of these nutrients, the plants will be affected.  For example, soil that is deficient in nitrogen will produce plants with yellow leaves, and soil that is deficient in phosphorus will have red leaves.  I found it interesting to learn the plant will take the nutrient from the older leaves and supply it to the newer leaves; therefore, it is the older leaves that change color first.

                Nutrient deficiencies can be corrected by adding organic or non-organic fertilizers.  Processed fertilizers work faster and make their nutrients available to plants quicker.  Organic fertilizers release their nutrients more slowly, making the nutrients available to the plant over the growing season.  There are some organic fertilizers, such as fresh manure and fish meal, which contain available nutrients.  Some nutrients are not even available for the plants until the next growing season.  “Repeated application of organic fertilizers builds up a pool of material that releases nutrients very slowly.  In the long run, this nutrient supply decreases the need for supplemental fertilizer.”

                Gardeners can determine the need for fertilizer and how much by having their soil tested every few years.  If the pH level is too low, lime can be added.  If the pH level is too high, elemental sulfur or iron sulfate can be added.

                I have learned a lot about soil and its effects on plants and realize there is much more knowledge to gain as well as how to apply it in my garden.  The Master Gardener course is very interesting and worthwhile to me.