Nitrogen (N): Plants are short, leaves tend to be pale green-yellow in colour, especially on the older foliage. On tomato plants, the undersides of the leaf and stems can develop a purple colouration.
Phosphorus (P): Plants are usually stunted, and a dark green colour. Symptoms occur on the older leaves first and plant maturity is often delayed. Phosphorus deficiency in some plant species can be due to conditions being to cold for uptake of this element, rather than a lack of phosphorus in the nutrient solution.
Potassium (K): The older leaves become yellowed with scattered dark (brown or black) spots, followed by tissue death. Severe deficiency will stunt the plant and all foliage will become yellowed and curled. On lettuce the leaves may take on a yellowed, bronzed appearance starting on the older foliage.
Sulfur: Deficiency of sulfur is not common - there may be a yellowing of the leaves, first seen on the new growth.
Magnesium: Deficiency is common on tomato crops with the older leaves developing yellowed areas between the veins which stay green.
Calcium: Young leaves are affected before older leaves and become distorted, small in size with spotted or necrotic (dead) areas. Bud development is inhibited and root tips may die back. Tipburn on lettuce is a symptom of calcium deficiency but is also caused by other factors not associated with a solution deficiency. Blossom end rot of tomatoes is also caused by a deficiency of calcium within the fruit tissue (not necessary in the nutrient solution), and is more of a `calcium transport' problem within the plant under certain environmental conditions.
Iron: Deficiency shows as a distinct yellowing between the leaf veins which stay green, on the new growth and younger leaves (this distinguishes it from magnesium deficiency which shows first on the older leaves). On crops such as tomatoes, iron deficiency may show when conditions are to cold for uptake, rather than be caused be an actual deficiency in solution
Chlorine: Deficiency shows as wilted leaves which then become yellowed and necrotic, eventually turning a bronze colour. Roots become stunted and thickened near the tips.
Manganese: Initially, an interveinal yellowing on the younger or older leaves, depending on the plant types. Brown, dry areas may develop and leaves may drop.
Boron: Plant size is usually reduced, the growing point may die back. Root tips often become swollen and discoloured. Leaves eventually become thickened, brittle, and may be curled with yellow spotting.
Zinc: Short plants with a reduction in internode length and leaf size. Leaf edges may be distorted or puckered, Yellowing between the leaf veins may also develop.
Copper: Deficiency is rare, but young leaves may become dark green and twisted or misshapen, often with brown, dry spots.
Molybdenum: Older leaves develop interveinal yellowing, progressing to the younger leaves. Leaf edges may develop scorching or cupping of the leaves.
Solution Strength - Under and Over Use, Measurement
Provided the nutrient you are using is complete and balanced, the concentration or strength of the solution has major effects on plant growth and development. This is why it is essential to be able to measure solution concentration, using a meaningful unit of measure. Many growers will still be working in ppm, using TDS meters, however there is now an industry move to standardise the unit of solution measurement to EC (electrical conductivity) which is a more accurate and meaningful way to monitor your nutrient. All a TDS or ppm meter actually does is to measure the EC of the solution, then use an approximate conversion figure to convert this to PPM. The problem arises is that this conversion figure is never very accurate, as different nutrient solutions with different compositions of nutrient elements will have different PPM values so using one conversion figure can be extremely inaccurate. What the plants root system is actually responding to is the EC (or osmotic concentration) of the nutrient so this is what we should measure. There are a number of different EC (sometimes called CF) meters, and the `water resistant' pen type meters are commonly used by growers. Depending on where in the world you are, the units expressed on your meter may be different, however it is easy to convert between the different units of EC.
