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Soil
Program Notes

Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. The Earth's body of soil is the pedosphere, which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil.

Soil interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere.  The term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution).  Accordingly, soils are often treated as a three-state system of solids, liquids, and gases.

Soil is a product of the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and its parent materials (original minerals) interacting over time.  It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, it is considered an ecosystem by soil ecologists.

Soil science has two basic branches of study: edaphology and pedology. Edaphology is concerned with the influence of soils on living things.  Pedology is focused on the formation, description (morphology), and classification of soils in their natural environment.  In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock.  Soil is commonly referred to as earth or dirt; technically, the term dirt should be restricted to displaced soil

Soil is a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming, to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil is an important carbon reservoir, and it is potentially one of the most reactive to human disturbance and climate change.  As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification).  This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover.

Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services.  Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and in the main still unexplored.  Soil has a mean prokaryotic density of roughly 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter (gram) of seawater.  Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter; tillage usually increases the rate of soil respiration, leading to the depletion of soil organic matter.  Since plant roots need oxygen, ventilation is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival.

A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other.  The pore space allows for the infiltration and movement of air and water, both of which are critical for life in soil.  Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms.

Source: Wikipedia

Eight Chemical Elements in Soil

There are a wide variety of chemical elements that go to make up soils. Some are detrimental to plants if present in too high a quantity – such as aluminum and lead – while others are used by plants in various chemical and metabolic processes to help them grow and reproduce, and can cause growth and yield problems if not sufficiently available. The availability of chemical elements will vary according to the conditions acting on your permaculture plot, such as the soil composition, the amount of rainfall, and the pH of the soil. Fortunately, they are easy ways for permaculture gardeners can ensure plants have access to sufficient levels of them. Here are ten chemical elements essential to all plants.

 

Potassium

Considered a macronutrient because of the high quantities a plant needs in order to thrive, potassium aids the healthy growth and reproduction of plants. It helps regulate water uptake and transpiration, the

activation of enzymes and the processing of protein. As such, a deficiency of potassium results in stunted growth, a weakening of root systems and poor crop production. So, getting a good amount of potassium in the soil for plants to use is crucial. As with many elements, increasing the amount of organic matter in soil, through compost and mulch, is a good way to provide plants with the potassium they need, but adding wood ash from hardwoods or kelp meal are other organic ways to increase the presence of this element.

 

Calcium

Calcium is important to plants in a similar way as to humans – it helps to support their structure. While human bodies use calcium in the formation of bone, plants use it in the formation of cell walls. By strengthening cells the calcium plays a role in protecting the plant against disease and heat stress.

The element remains in the cell walls so, unlike many of the other elements a plant uses, it does not circulate through the stem and leaves. The plant takes up calcium in a soluble form during the process of

transpiration, often forming a compound with phosphorous. As such, areas of low rainfall and cold temperatures may find calcium levels in plants to be low. Gardeners who find young leaves and shoots curled or scorched, or damage to fruit may have a calcium deficiency.

 

Phosphorous

Phosphorous is a key driver in a plant’s metabolic processes – namely photosynthesis, the transfer of the energy produced by photosynthesis to all parts of the plant, and the breakdown of carbohydrates. Plants take up phosphorous in a soluble form, and because most phosphorous in soil is actually in an

insoluble form, it is important that the permaculture gardener ensures that there is a good supply, as well as sufficient moisture. If plants lack phosphorous they are likely to show purple coloring on older leaves. Fish and bone meal added to the soil is the quickest organic way to up phosphorous levels.

 

Nitrogen

Nitrogen is arguably the most important element required by plants. It is certainly the nutrient that is needed in the largest quantities to ensure healthy growth. Plants use nitrogen in the formation of proteins – the building blocks of the plants’ structure – and chlorophyll, essential to its production of

energy. Bacteria and microorganisms transform nitrogen in organic matter into nitrates that are then available to plant roots to take up. Some plants, notably the legumes, work in conjunction with bacteria

to ‘fix’ nitrogen in their root nodules, from where other plants also access it so planting a leguminous crop within a guild is a common permaculture technique of ensuring a good supply of nitrogen.

 

Iron

Iron in soil primarily comes from the breaking down of mineral deposits such as rocks and stones. Plants only use it in small amounts, but these low levels still play a crucial role in the plant’s formation of

chlorophyll and its enzyme activity. Iron also helps the plant fix and process nitrogen. The plants do not take up iron through the transpiration of moisture, rather it is gathered via chemical processes in the

roots. If soil is too alkaline, this can inhibit iron intake. Adding composted animal manure is a good method of increasing iron levels in the soil.

 

Magnesium

An essential building block of chlorophyll – the green pigment that has a role in photosynthesis – magnesium also aids the plant with respiration and the synthesis of nitrogen. Magnesium becomes available to plants through organic matter, becoming soluble in moisture for uptake by plants.

Thus, areas of dry soil conditions can suffer from magnesium deficiency, which will affect crop yield. Symptoms of deficiency include pale leaves and red spots on leaves. Because magnesium is a mobile element, moving around the plant to combat low levels, signs of a lack of the element are likely to appear on older and lower leaves. Organic matter is the best way to supply magnesium to the soil.

 

Zinc

While plants only need zinc in small amounts, it is essential to their development as it aids in the synthesis of proteins and the production of growth hormones. As such, it helps to ensure a good crop from a plant. Indeed, crops such as wheat and corn are particularly susceptible to a lack of zinc,

making the supply of this element one of the primary drivers of inorganic fertilizer application in monoculture agricultural systems. If the soil has a zinc deficiency, crops may be reduced in number, with

uneven fruit and vegetable formation and poor ripening. Symptoms of a lack of zinc include stunted growth and distorted leaves, including irregular coloring such as striping or dotting. Keeping the soil supplied with organic matter is the best way to ensure zinc levels are sufficient.

 

Copper

Copper is essential for proper enzyme activity in plants, as well as robust seed development and chlorophyll formation. A deficiency is evidenced by the tips of leaves becoming twisted or dying back. Finer textured soils generally contain more copper, as do soils that have a lower pH. Because copper forms bonds with particles of organic matter, adding compost to soil helps ensure a good supply of this element to plants.

 

Source: Regenerative.com

 

 

Soil


 

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