Occasionally two or more nutrients will run short at the same time. If the nutrients are deficient, or too abundant, then plants will be discolored or deformed. The deficiency symptoms will indicate which nutrient or nutrients are needed. However, it is much better to supply additional nutrients before deficiency symptoms appear. A soil test will tell which nutrients are low before growth is affected.
Nitrogen deficiency causes reduced growth and pale yellowish green leaves.
The older leaves turn yellowish first since the nitrogen is readily moved from the old leaves to the new growth. If the soil is cold and wet, nitrogen in the soil is not as available to the plants. Excess nitrogen may cause potassium deficiency. Phosphorus, P, is important in the germination and growth of seeds, the production of flowers and fruit, and the growth of roots. Phosphorus deficiency causes reduced growth and small leaves that drop early, starting with the oldest leaves.