How do different amounts of fertilizer affect plant growth?

Written by joshua tuliano
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How do different amounts of fertilizer affect plant growth?
The right amount of fertiliser leads to healthy plant growth (Plant image by Hedgehog from

Fertiliser is any substance such as manure or a mixture of nitrates used to make soil more fertile, states the Princeton University website. Organic and synthetic fertiliser is composed of macronutrients and micronutrients that facilitate healthy plant growth and fertility. The right amount of fertiliser is crucial for healthy plant growth as too little fertiliser causes stunted growth, and too much causes plant burn.

Primary Macronutrients

Nitrogen, phosphorus and potassium are the three primary nutrients in all types of fertiliser. Nitrogen promotes cell division leafy green growth, and is the limiting factor for plant growth, according to the Oulu University website. Phosphorus aides the plant with photosynthesis and fruit production and is found in small quantities naturally without the aid of fertiliser. Potassium helps plants absorb the other two macronutrients, thus promoting healthy growth. The primary macronutrients make soil fertile by providing the essential nutrients needed for healthy plant growth.


Micronutrients in fertiliser are composed of boron, copper, iron, magnesium, molybdenum and selenium. The micronutrients in fertiliser are not found in high quantities, and are used in various concentrations for different plant varieties. According to United States Department of Agriculture website, crop such as alfalfa and celery need high concentrations of boron, whereas onions and peppermint require low levels of boron. The micronutrients aid in plant growth for some plants, but can be dangerous in high levels for other plants due to their tolerance of the element.

Soil Testing

Soil can have different nutrient levels in different areas, but soil tests can determine the nutrients needed for each area. Soil testing prevents under-fertilisation and over-fertilisation for your crops or plants. According to the University of Hawaii's website, soil samples should be tested every one to five acres in each test area. University-based or private labs test soil nutrient levels for a nominal fee, and hardware lawn and garden stores sell soil-testing kits, an easy way to determine how much soil to extract.


Plants need the right amount of macro and micronutrients in order to facilitate healthy growth. Fertiliser adds nutrients to soil, that through previous growing, becomes depleted. Using too little fertiliser on your plants will limit the growing ability of the plant. Low levels of nitrogen slows and limits plant growth and colour, whereas low levels of phosphorous affects the reproductive and flowering abilities of all plants. Low levels of potassium affects the amounts of macronutrients absorbed by plants. The correct levels of micronutrients are determined by the specific crop, but are important for all healthy plant growth.


Too much fertiliser leads to a variety of plant problems including, plant burn, disease susceptibility and plant death. An excess supply of macronutrients is what causes plant damage, whereas an excess supply of micronutrients is crop specific and typically not found in high quantities in fertiliser. An overabundance of nitrogen leads to leafy green growth, but makes the plant weak and susceptible to insects, plant burn and disease. Fortunately, phosphorus and potassium are not found in high quantities in soil, which makes damage from over fertilisation from these two elements very unlikely, according to the Soil Science Education website powered by NASA.

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