Why Plants Suffer from Nutrient Deficiencies and Toxicities
Many nutrients are essential for healthy plant growth and function. They make up the cells of the plants, form plant DNA and help plants photosynthesise to produce vital sugars among many other things. When a plant doesn't have enough of a particular nutrient, it cannot make cells, DNA, sugars or any of the other important components of a plant and so this is called a nutrient deficiency. When a plant has too much of a nutrient, it might not be able to take up enough of another nutrient or the excess nutrient may make the plant sick in the same way that a person will get sick if they eat too much fatty food. Think of it this way, fat is important for humans because it allows us to take in and store certain nutrients and because it gives us energy but too much fat isn't a good thing because increases the risk of many diseases and causes a range of other problems. The same sort of thing happens in plants. Nutrient toxicities and deficiencies may occur in plants because the soil doesn't contain enough of the nutrient or because it contains too much. Not all symptoms in plants are the result of an excess or lack of nutrient in the soil though. Often, symptoms of nutrient toxicity or deficiency in plants are due to problems with the plant's uptake of one or more nutrients. This may be because something is affecting the plant's ability to absorb the nutrient (too little water prevents calcium uptake for instance) or because something is affecting the availability of the nutrient (for instance soil pH can drastically alter how much of an element in the soil is in the form that plants can use).