A key component of GlobalNet Academy’s horticulture certificate I, II and III courses in Tasmania is understanding the various nutrients required for healthy plant growth and their origins in the soil.
It’s to get confused over which nutrients your plants need for healthy growth. For many of us, our last interaction with chemical elements was in high school and things may have become a little hazy over the intervening years. So, lets brush up on a little soil chemistry.
In basic terms, the mineral nutrients that your plants need access to, via their growing media, can be broken down into three groups; the 3 Primary macronutrients, the 3 Secondary macronutrients and the 7 micronutrients.
The three Primary Macronutrients are:
Nitrogen – Nitrogen is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy. It helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops.
Nitrogen often comes from fertilizer application and from the air (legumes get their N from the atmosphere). Chicken manure is a good source of nitrogen.
Phosphorus – Like nitrogen, phosphorus (P) is an essential part of the process of photosynthesis. It is involved in the formation of all oils, sugars, starches, etc. Phosphorus also helps with proper plant maturation and withstanding stress. In general, phosphorous encourages blooming and root growth in most plants.
Phosphorus often comes from fertilizer, bone meal, and superphosphate.
Potassium – Potassium is absorbed by plants in larger amounts than any other mineral element, except nitrogen and in some cases, calcium. It helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.
Potassium is supplied to plants by soil minerals, organic materials, and fertilizer.
The three Secondary Macronutrients are:
Calcium – Calcium is an essential part of plant cell wall structure. It provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant.
Sources of calcium are dolomitic lime, gypsum, and superphosphate.
Magnesium – Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth.
Soil minerals, organic material, fertilizers, and dolomitic limestone are sources of magnesium for plants.
Sulphur – An essential plant food for production of protein, sulphur promotes activity and development of enzymes and vitamins. It helps in chlorophyll formation, improves root growth and seed production and helps with vigorous plant growth and resistance to cold.
Sulfur may be supplied to the soil from rainwater. It is also added in some fertilizers as an impurity, especially the lower grade fertilizers. The use of gypsum also increases soil sulfur levels.
The seven Micronutrients are:
Boron – Helps in the use of nutrients and regulates other nutrients.
It aids production of sugar and carbohydrates and is essential for seed and fruit development. Sources of boron are organic matter and borax.
Copper – Important for reproductive growth. Copper aids in root metabolism and helps in the utilization of proteins. Copper sulphate and copper oxide are commonly used to add copper to soils.
Chloride – Aids in plant metabolism and is essential in the process which opens and closes a plants stomata. Sources of chlorides include rainwater and atmospheric dust. It rarely needs to be added by the gardener.
Iron – Essential for formation of chlorophyll. Common sources of iron are iron sulphate and iron chelate.
Manganese – Acts with enzyme systems involved in the breakdown of carbohydrates, and nitrogen metabolism. Epsom salts (diluted) are a source of manganese for your garden.
Molybdenum – Functions with enzyme systems involved in the breakdown of carbohydrates and nitrogen metabolism. It is contained in micronutrient foliar sprays and adding lime to a soil will increase the amount of molybdenum available to your plants.
Zinc – Essential for the transformation of carbohydrates. Zinc also regulates consumption of sugars. Zinc is part of the enzyme systems that regulate plant growth. Sources of zinc are soil, zinc oxide, zinc sulphate and zinc chelate.
Adding a trace element fertiliser or foliar spray is a good way of applying these micronutrients. Remember, the micronutrients are needed in very low amounts and can be detrimental to your plants if they are over used.
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