Potassium and Phosphorus in Crops: Fruit Size, Color, Brix and Rooting
Quick answer:potassium is the quality nutrient: it's involved in sugar transport, color, size, firmness and flavor (Brix degrees) of fruit, and helps the plant tolerate heat, drought and frost. It's applied mainly during bulking and ripening. Phosphorus is the energy and root nutrient: it promotes rooting, flowering and fruit set, so it's applied at the start of the crop cycle and before flowering.
When does the crop need potassium?
Bulking and ripening: this is when fruit demands the most potassium.
Before heat waves or frost: potassium regulates stomatal opening and improves tolerance to heat and water stress.
Deficiency symptoms: yellow or dry margins on older leaves, small fruit, poor color and weak flavor.
When does the crop need phosphorus?
Transplanting and rooting: so roots develop quickly.
Pre-flowering and fruit set: phosphorus helps pollen tube formation and fertilization.
Deficiency symptoms: slow growth, dark green or purplish leaves, poor flowering.
Natural mineral with no chemical treatment, 18% K2O
Poor or demineralized soils
Fertigation 250-300 g/ha
For post-transplant start-up, Trasplante Vital combines phosphorus and potassium with amino acids and seaweed.
Application tips
Split potassium into several applications during bulking rather than a single large dose.
Don't overdo potassium in soils low in magnesium or calcium: too much can hinder their absorption.
Phosphorus is easily locked up in calcareous soils; easily absorbed liquid formulations and good pH management help (see how to correct pH).
Frequently asked questions
Which fertilizer raises the Brix degrees of fruit?
Potassium is the nutrient most closely tied to sweetness, since it's involved in the synthesis and transport of sugars. A fast-acting potassium such as Potasia Acida, applied during the ripening stage, favors better Brix degrees.
Can potassium be applied during flowering?
During flowering, phosphorus and boron are usually prioritized. Potassium takes on a bigger role from fruit set onward, and especially during bulking and ripening.
Does potassium help against frost?
Yes: a good potassium level increases the concentration of salts and sugars in cells and improves the plant's tolerance to cold and heat.
Need a fertilization plan for your crop? Ask our technical team for advice. Also see: calcium for fruit firmness.
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