All the nutrients listed in Table 2-4 are essential for plant growth. The roles and deficiency symptoms of the primary nutrients are discussed below. The symptoms are rarely clear cut, so it is important to use both soil and plant analyses when trying to diagnose a suspected nutritional problem. It also is an integral part of the chlorophyll molecule and thus plays a key role in photosynthesis. An adequate supply of nitrogen is associated with vigorous vegetative growth and a plant's dark green color.
Nitrogen deficiency is characterized by reduced plant growth and a pale green or yellow color.
This yellowing generally begins at the tip of the leaf and goes down the middle of the leaf. If the deficiency is severe, the affected area eventually turns brown and dies. Since nitrogen is mobile in the plant, older leaves show the first symptoms of nitrogen deficiency. Considered essential to seed formation, this mineral is often found in large quantities in seed and fruit. Phosphorus is essential for the biological energy transfer processes that are vital to life and growth.