<Li> with mycorrhizal fungi, which through their association with the plant roots help to create a larger effective root surface area . Both of these mutualistic relationships enhance nutrient uptake . </Li> <P> Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants harbour nitrogen - fixing bacteria, so most plants rely on nitrogen compounds present in the soil to support their growth . These can be supplied by mineralization of soil organic matter or added plant residues, nitrogen fixing bacteria, animal waste, through the breaking of triple bonded N molecules by lightning strikes or through the application of fertilizers . </P> <P> At least 17 elements are known to be essential nutrients for plants . In relatively large amounts, the soil supplies nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur; these are often called the macronutrients . In relatively small amounts, the soil supplies iron, manganese, boron, molybdenum, copper, zinc, chlorine, and cobalt, the so - called micronutrients . Nutrients must be available not only in sufficient amounts but also in appropriate ratios . </P> <P> Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone . Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high . Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice versa . An abundance of one nutrient may cause a deficiency of another nutrient . For example, K uptake can be influenced by the amount of NH available . </P>

How many essential plant nutrients are provided by soil
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