ABSTRACT
All the plant’s nutrients can be derived from the soil solution, with the exceptions of carbon and oxygen, which reach the plant mainly via the leaf, being essential ingredients in the processes of photosynthesis (see p. 92) and respiration (see p. 99). Although the soil-based chemicals are primarily taken up by the root, they can be taken in through other parts of the plant, e.g. in foliar feeding. Most gardeners who feed their plants with fertilizers will have noted that the main nutrient contents listed on the containers are nitrogen, phosphorus (also known as phosphate) and potassium (also known as potash). These are the major nutrients because they are needed in relatively large quantities. Also needed in quite large quantities are magnesium, calcium (usually supplied in lime) and sulphur. Iron is an example of a nutrient that is essential, but needed in much smaller quantities. Iron, along with manganese, boron, zinc, copper and molybdenum, is referred to as minor nutrient or trace element. A summary of all the major and minor nutrients is given in Table 20.1 , which also provides an indication of how much of each is in a healthy plant. The major nutrient contents of most of the fertilizers used in horticulture are given in Table 20.2 .
