Signs and causes of phosphorus deficiency in crops

Phosphorus deficiency can most often be observed when cultivating plants in soils that are: 1) sod-podzolic; 2) of a heavy particle size distribution; 3) poorly drained; 4) high in acidity or alkalinity (carbonates); 5) low in organic matter, as well as in other cases on different soils, for example, when applying high doses of nitrogen and potassium fertilizers against a background of low levels of phosphorus available to plants.

For the majority of crop plants, the most characteristic signs of phosphorus starvation are: growth retardation and small size of young leaves, dark green leaf color with a purple or bluish hue, the formation of purple, reddish, or brown spots on them, and tissue necrosis in the affected areas. Symptoms appear first on older, lower leaves and gradually spread upward along the plant.

A lack of phosphorus in plants, resulting from a disturbance in the normal ratio with nitrogen uptake, has a sharply negative effect on the progression of growing season phases and the formation of reproductive organs: flowering and ripening are delayed, the number of fruits and seed is reduced, and their quality deteriorates.

Indicator plants for phosphorus starvation: tomatoes, turnips, swedes, apple trees, gooseberries.

In potatoes, phosphorus deficiency affects shoot growth and is particularly evident during the budding and flowering phases. Lateral branching is weak or absent, which causes the bushes to have a compressed shape. Leaves are dark green and grow from the stem at an acute angle.

During the tuberization period, a narrow dark brown or black stripe appears on the tips of the lower leaves; the dead tissue curls upward in the form of a narrow tube. The leaves remain dark green until harvesting; a small portion of the lower leaves falls off. The onset of the budding and flowering phases is delayed by several days. Rusty-brown spots appear in the tuber flesh, which remain hard when the potato is boiled and stand out against the soft, cooked mass of the tuber. Similar changes in tubers can also be caused by other reasons, such as viral diseases.

In grain legumes, symptoms of phosphorus starvation are not clearly manifested, however, some of them are quite characteristic and, with careful observation, allow for a correct conclusion regarding the plants' need for phosphorus. In this case, there is a slowing of growth and plant elongation; leaves have a dark or blue-green color. In some legumes, the leaf blades curl upward and the leaves appear pointed; later, the stems may turn red. Flowering and fruiting are delayed.

In tomatoes, in the case of phosphorus deficiency, the cotyledons of seedlings are directed upward at an acute angle; later, a crimson color appears on the lower surface of the bluish-green leaves with a purple or violet tint; the veins gradually become violet-red; later, in cases of severe starvation, the entire above-ground part acquires a crimson color. The stems are thin, fibrous, and stiff; fruits set and ripen late. Roots become covered with a rusty coating.

For cabbage, the following signs are characteristic of phosphorus deficiency: dwarf growth, small size, and a dull dark green color of the leaves with a violet or purple tint. Such pigmentation appears first on the veins and is more pronounced along them, and then spreads, starting from the tip, to the entire surface of the leaves.

Diagnosis of phosphorus starvation in vegetable crops

Phosphorus starvation in onions manifests as growth retardation, wilting, and necrosis of the tips of older leaves, the appearance of mottling on the leaves, the alternation of areas with green, yellow, and brown colors, and the blackening of dead leaves.

In radishes, phosphorus deficiency manifests as a reddening of the lower surface of the leaves.

Symptoms of phosphorus deficiency in fruit crops

In fruit and berry crops, phosphorus starvation is characterized by the following symptoms:

• dark or bluish-green, dull leaf color;
• a reddish, bronze, or crimson tint to their petioles, veins, and lower surface, as well as to young shoots;
• weak branching;
• short and thin shoots;
• bronze or ocher(rusty)-green leaf color, the appearance of yellow or dark green spots on them (mottling);
• upright position of the upper leaves, curling downward of their edges and tips (especially in peaches);
• premature leaf fall (sometimes the appearance of new leaves).

The signs appear on the entire tree but are localized primarily on the lower leaves of the current year's shoots, especially often during prolonged cold weather throughout the spring-summer period, as well as in the first year after transplanting nursery plants to a permanent location.

Fruits and berries are small, have a poor taste, and ripen slowly; fruiting is weak.