Major or macro-nutrient deficiencies (cucumber)

Nitrogen deficiency

Nitrogen deficiency
Compare the grossly stunted pale plantlacking in flowers and fruit (left) with a healthy plant (center). Older leaves turn a uniform pale green to yellow; this condition spreads to younger leave sup the plant (right).
Most plants need nitrogen in large amounts. It is generally considered to drive plant growth, probably because its supply is often limiting. A shortage of nitrogen reduces the plant's capacity to trap energy through photosynthesis. Nitrogen is required in the production of chlorophyll (the green pigment in leaves), which is responsible for converting sunlight to usable plant energy.
Both vegetative growth and fruit production are severely restricted when nitrogen supply is inadequate. Plants appear pale and spindly. New leaves are small but remain green, whereas the oldest leaves turn yellow and die. If the problem is not corrected, the yellowing spreads up the shoot to younger leaves. Yield is reduced and fruit are pale, short and thick.
Treatment
Side-dress deficient in-ground crops with 20–50 kg N/ha, or apply fortnightly foliar sprays of 2% urea at high volume. To prevent possible salt burn to leaves when applying any foliar spray, spray late in the afternoon or during cloudy weather.
For crops grown in soilless media, use a nutrient solution containing 150–200 ppm N.
Phosphorus deficiency
Australian soils generally are low in phosphorus, so they must be regularly supplemented with fertilizer. Plants require phosphorus at all stages of growth, but demand is greatest during crop establishment and early plant growth. If phosphorus becomes limiting, it is translocate from older to younger tissues, such as the leaves, roots and growing points. In a crop such as cucumbers, which has a succession of new vegetative and fruiting tissues, a regular supply of phosphorus (and other elements) is needed to ensure that the plant can sustain quality fruit production over a prolonged period.
Phosphorus-deficient plants have weak roots, are stunted, and produce small, dark, dull, grey-green leaves. The oldest leaf, at the base of the shoot, turns bright yellow. However, unlike nitrogen deficiency, the leaf directly above this leaf remains dark green. Brown patches appear between the veins on mature leaves. These become scorched and spread until the leaf dies prematurely. Fruit set is reduced and so production is impaired.
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