Plant nutrients

Soils contain most of the nutrients needed for plants to grow. These nutrients are taken in from the soil by the roots of growing plants and carried through the roots into the growing plant above ground. This is how plants get much of their nourishment or food. Remember, plants don't just need sunlight and water to live - they also need soil nutrients! Many school textbooks seem to forget this.

Soils contain about 18 nutrients that are important and even vital to plants. Some of these, termed macronutrients, are needed in fairly large amounts, nutrients such as calcium, magnesium, potassium, similar to what we humans need for growth and health. Other nutrients, called micronutrients, are needed in much smaller amounts but are also essential for a healthy plant. These include iron, zinc, copper, boron. All of the 18 nutrients are required by plants. Many of these nutrients are present in the rocks from which soils are derived and have been introduced into soil as rocks are broken down to form soil. Others reach the soil through the rotting and breakdown of dead organic matter.

In soil these nutrients can be held either on the edge of mineral particles or dissolved in soil water. As roots grow through soil and take up water, they also take in nutrients. These are passed up through the roots to the parts of the plant above-ground. In addition to this route there is another very beneficial one, that between fungi, termed mycorrhizae, and roots. Mycorrhizae take up nutrients, particularly phosphorus, and pass them into the roots of plants. In natural situations, such as woodlands, nutrients are constantly recycling between soils and plants. Dead plants fall to the ground and are broken down to release nutrients, which then take part in the next cycle of growth. With agriculture, when the crop is harvested, all the nutrients in the plants are also removed from the field and this important recycling of nutrients is not possible. The farmer must then add extra nutrients to the soil - that is what fertilizer or farmyard manure does by maintaining soil fertility and productivity for the next crop. Soils are cultivated worldwide to produce food for the world's fast growing population. This requires careful management of soil to ensure there are sufficient nutrients in the soil for the following years' crops.