The information below is from the California Master Gardener Handbook, Second Edition.
Nitrogen – Important for many growth and developmental processes; important in photosynthesis; backbone in DNA.
Symptoms of Deficiency – Slow growth, stunting and yellow-green color; more pronounced in older tissue; “firing” of tips and margins (turning brown and dying); premature death.
Symptoms of Excess – Excessive vegetable growth, dark green color, excessive transpiration, reduced yield; delay maturity; few fruit.
Phosphorus – Important for energy systems; stimulates early growth and root formation; promotes seed formation; important in photosynthesis.
Symptoms of Deficiency –Slow growth, stunting, and purplish color on foliage or dark green color; dying leaf tips; delayed maturity; poor fruit or seed development.
Symptoms of Excess – Excess can interfere with micronutrient absorption; may mimic Zinc deficiency.
Potassium – Affects membrane permeability and H+ relationships, stomatal opening/closing, internal water relations, cell division, starch and protein synthesis, and sugar translocation; increases size and quality of fruits and vegetables; decreases disease resistance.
Symptoms of Deficiency – Slow growth; leaf tip and marginal burn and necrosis (starts on more mature leaves); weak stalks; small fruit and shriveled seed.
Symptoms of Excess – Light green foliage; tendency for Ca2+ and Mg2+ deficiency symptoms to appear.