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Growing Guide

Natural Nutrients

Read all about the elements plants need and how they contribute to the biological health of your garden

Natural Nutrients - The Elements Plants Need

Plants get carbon (C), oxygen (O) and hydrogen (H) from water (H2O) and carbon dioxide (CO2) in the ground and air. These three elements are the 'backbone' of the organic (carbon) chemistry of all life on Earth, and they make up over 95% of the dry matter of plants.

Other essential elements are, Nitrogen (N), Phosphorous (P), Potassium (K), Sulphur (S), Molybdenum (Mo), Magnesium (Mg), Iron (Fe), Manganese (Mn), Boron (B), Copper (Cu), Zinc (Zn), Calcium (Ca), Chlorine (Cl) and Nickel (Ni).

If the soil does not contain the nitrogen, phosphorus, potassium and other elements that the plant needs to function properly it will sicken, become weak and more susceptible to diseases caused by some fungi, bacteria and viruses.

These elements can be supplied as mined or synthetic fertilisers or as natural organic material. So long as these provide the appropriate levels of the elements in a form the plant can make use of it doesn’t matter to the plant. However, the form of fertiliser can have a significant influence on the biological health of the soil and consequently the health of the plants growing in it.

All soils are largely made up of tiny mineral particles. The size of mineral most abundant in your soil determines whether you have sand, loam, or clay soil. The other ingredients of soil include organic matter (living and non-living), water and air. The living and previously living contents of the soil form a large proportion of healthy soils; healthy in that they provide a good substrate for healthy growth of plants. There is a food web of living and dead organic material in soils in which the organisms exchange energy and nutrients. As well as these live organisms there is much dead material which the decomposers, detritovore and scavengers reduce to humus. Humus is the mix of complex organic compounds that are difficult to break down and provide essential water retention, soil structure and slow release energy for soil organisms. Humus gives good soil its deep dark brown colour.

There are harmful pests and diseases that can be found in garden soils, but these harmful organisms are vastly outnumbered by organisms that are either harmless or beneficial to your plants. Promoting the ‘good’ organisms and the conditions that they prefer helps them outcompete the harmful organisms and reduce the risk of them causing disease or harm to your plants.

The Benefits of a Healthy Living Soil

  • Mycorrhizae are fungi that form a symbiotic relationship with plants. The fungi grow their hyphal filaments around or into the roots of their host plants, this area is known as the rhizosphere. The fungi are better able to absorb nutrients and water from the soil and pass them on to the roots. In return the plants provide sugars to the fungi made by the plants’ photosynthesis.
  • A range of different micro-organisms can fix nitrogen from the air and convert it to nitrate, nitrite, ammonia and other compounds that plants can use. The most well-known are the rhizobia bacteria in the root nodules of legumes such as peas and clover.
  • Soil micro-organisms, invertebrates and larger animals play the major part in re-cycling dead plant and animal material. The leaf litter, grass clippings, fallen branches, etc. decay through consumption by soil organisms. This digestion releases mineral nutrients and breaks down the larger organic (carbon based) molecules such as lignin and cellulose, to smaller molecules. The smaller molecules can then be used by micro-organisms as a food source. This organic material is known as humus or humic substance and is very important for the condition of soil.
  • Available water is a most important property of a fertile soil. The most important effect of humic substances in the soil is their ability to hold water during periods of drought. Soils with good crumb structure have more open spaces which allow for gaseous interchange with the atmosphere, and for greater water infiltration. Humic substances are key components of a loose crumb soil structure.
    Humic substances in soils help neutralize the pH of those soils. Both acidic and alkaline soils are neutralized; moved towards a healthy pH neutral (7.0).
  • Invertebrates such as earthworms, insects and even burrowing animals help distribute the humus and nutrients deeper in the soil, helping develop a deep humus rich topsoil. They also help aerate the soil keeping it suitable for aerobic organisms and easing plant root penetration.
  • Carbon sequestration - Soils with greater amounts of soil life and humus contain larger amounts of carbon which has been sequestered from CO2 in the atmosphere, helping reduce this greenhouse gas.

How to Encourage Beneficial Life in the Soil

  • One of the most important ways to encourage the good organisms in the soil is to provide natural nutrients and fertiliser.
  • Keeping the soil covered with mulch, straw or leaf litter is the first step in promoting soil life. A living ground cover of plants is even better. Plants devote considerable energy to encouraging soil organisms by secreting sugars, vitamins and other organic compounds into the soil.
  • Provide your soil with organic material on which the soil organisms can feed and break down to humus. This organic material can be in the form of compost, well-rotted manure, seaweed or humates and humic acids.

Soil provided with nutrients in natural forms will be full of beneficial organisms that can convert the natural nutrients to forms that your plants can use and all the elements the plants need.

21 September 2020