Corn Nutrition Diagnostics

Last updated: June 22, 2025

Visual diagnostics

Nitrogen deficiency

Corn is very sensitive to nitrogen deficiency. Symptoms of shortage appear even with a slight deficiency.

It manifests on:

soils with low organic matter content;
light sandy soils leached as a result of excessive moisture;
soils depleted by intensive crop cultivation;
waterlogged soils;
acidic soils with pH below 6.0;
alkaline soils with pH above 8.0.

Symptoms

Plants are stunted, the stem is thin, with spindle-shaped stems, and leaves are pale green or yellow. Plants produce a small ear per plant; the ears have almost no kernels or the kernels are very small. Yield drops sharply.
Nitrogen is mobile in plants; under deficiency it is easily mobilized and moves from old to younger leaves. The first symptoms appear and are more pronounced on old leaves.
When deficiency occurs in the initial stages of development, plants look uniformly pale green to yellow. At later stages, old leaves become pale yellow, while young leaves remain green.
If the deficiency persists or occurs at a later stage of vegetation, pale yellow chlorosis develops at the tip of old leaves and extends to the leaf base along the midrib in a V-shaped pattern (a specific symptom of nitrogen deficiency in corn).
In mature plants, the following may appear simultaneously: young leaves are pale green, middle leaves are pale yellow to pale brown, and old leaves are dry.

Stages of deficiency development

Stage I: With mild deficiency, the whole plant looks uniformly light green.
Stage II: If deficiency increases, pale yellow chlorosis begins at the tip of old leaves and continues toward the base along the midrib in a V-shaped pattern.
Stage III: Brown necrosis begins at the leaf tip and continues toward the leaf base.
Stage IV: Old affected leaves become pale brown and die.

Management of nitrogen deficiency

Management of nitrogen deficiency includes:

agrochemical soil analysis before planting to determine available nitrogen content in the soil;
application of recommended amounts of nitrogen in the form of organic fertilizers, bio-fertilizers, nitrogen fertilizers;
side-dressing with soluble nitrogen fertilizers, for example, urea in two split doses;
for rapid recovery, foliar spraying with a 2% urea solution, carried out every 10–15 days;
inclusion of legumes in crop rotation.

Photos

Phosphorus deficiency

The development of phosphorus deficiency in corn is promoted by:

soils with low organic matter content;
alkaline and calcareous soils;
soils depleted by intensive crop cultivation;
soils whose top layer has been removed by erosion processes (wind or water erosion);
acidic soils with pH less than 6.0;
alkaline soils with pH from 7.5 to 8.5.

Since phosphorus is poorly mobile in the soil, any soil condition that retards root growth, such as cool temperature, wet or very dry conditions, or compaction, can lead to phosphorus starvation in plants.

In the early stages of development, plants of some hybrids may have purple leaves even with sufficient phosphorus; conversely, other hybrids may retain natural leaf color under phosphorus deficiency.

Symptoms

Plants are stunted with thin and narrow dark green leaves. The number and size of stomata in the leaves are reduced. Root growth is sharply slowed. Plants develop one small ear with few kernels, which leads to a sharp decrease in yield.
Phosphorus is mobile in corn plants; under deficiency it is easily mobilized, moving from old leaves to young leaves, so signs of phosphorus starvation appear first on old leaves, while young leaves usually remain normal.
Old leaves have a characteristic dark green or bluish-green color.
With severe phosphorus deficiency, purple or purple-red colors appear on old dark green leaves, starting at the edges of old leaves. The purple color is associated with the formation of anthocyanin in plant leaves, which accumulates when sugars cannot be transported to other plant organs; phosphorus participates in sugar transport processes.
Under conditions of severe deficiency, the purple color may cover the entire plant.
At the very latest stage of starvation, leaves dry out and die.

Stages of deficiency development

Development of phosphorus deficiency on corn leaves.

Stage I. The initial stage of phosphorus deficiency manifests as a dark green or bluish-green color on old leaves.

Stage II. If the deficiency persists and intensifies, the edges of old leaves acquire a purple or purple-red color, which usually begins at the leaf tip and develops toward the base.

Stage III. As symptoms develop, the entire leaf becomes reddish-brown or purple.

Stage IV. Under acute deficiency, brown necrosis develops at the leaf tip, moving from the edge to the leaf base.

Management of phosphorus deficiency

Management of phosphorus deficiency includes:

agrochemical soil analysis before planting to determine available phosphorus content in the soil;
application of recommended amounts of phosphorus in the form of organic fertilizers, phosphorus-mobilizing microbial cultures, phosphorus fertilizers;
if phosphorus deficiency is detected in crops, side-dressing with soluble phosphorus fertilizers, for example, ammonium phosphate, applied with irrigation;
maintaining soil acidity in the range of pH 6–7.

Surface application of poorly mobile forms of phosphorus fertilizers (superphosphates) and foliar feeding are ineffective when phosphorus starvation is detected.

If phosphorus shortage is detected, the areas where deficiency was found should subsequently be analyzed in order to eliminate insufficient available phosphorus content in the soil.

Photos

Potassium deficiency

The development of potassium deficiency in corn is promoted by:

soils formed on rocks with low potassium content;
light soils by soil texture, from which potassium has been leached under the action of excessive moisture;
soils with low organic matter content;
soils with wide sodium-to-potassium, magnesium-to-potassium, and calcium-to-potassium ratios;
irrigation waters with high bicarbonate ion content;
soils with acidity below pH 6.0.

In crops, potassium deficiency can appear locally, in individual patches.

The causes of potassium starvation in corn plants can be any causes restraining normal root system development: a dry surface soil layer at the beginning of the growing season, ridge cultivation, no-moldboard tillage system, localized soil compaction, compaction of the sidewall of the seed furrow, and shallow seed placement.

Symptoms more often begin to appear 4–6 weeks after planting, during the period when potassium consumption by corn plants is maximum.

Symptoms of potassium deficiency

Shortened internodes and stunting of plants, loss of dark green leaf color.
Small ears, which are often pointed and underdeveloped at the tips.
Potassium easily moves from old leaves to young leaves, so deficiency symptoms appear first on old leaves.
Young actively growing leaves draw potassium from old plant parts, so they usually remain green and healthy.
Symptoms begin to appear as pale yellow chlorosis at the tip and edges of old leaves.
After chlorosis, pale brown necrosis appears, which, like chlorosis, progresses from the leaf edge to the base. Marginal chlorosis and necrosis of old leaves are a specific symptom of potassium deficiency.
Under conditions of severe deficiency, red stripes appear at the base of the stem and leaves.

Stages of potassium deficiency development

Stage I. Mild potassium deficiency leads to slowed growth, thin stems, and pale green leaf color.

Stage II. Persistence and intensification of the deficiency lead to chlorosis on old leaves, which begins at the tips and edges of the leaves.

Stage III. Chlorosis intensifies and turns into pale brown necrosis, which, like chlorosis, progresses from the edge to the base, leaving the midrib and surrounding tissues pale green.

Stage IV. Under conditions of severe deficiency, affected lower leaves dry out and die.

Management of potassium deficiency

Management of potassium deficiency includes:

agrochemical soil analysis before planting to determine available potassium content in the soil;
restoration of acidic, alkaline, and saline soils;
advance application of organic fertilizers;
application of potassium fertilizers in accordance with recommended rates and agrochemical soil analysis;
if potassium deficiency is detected in corn crops, soluble potassium salts are used, for example, potassium nitrate, sulfate, or chloride, which are applied with irrigation water. Spraying is not recommended.

Full restoration of potential yield cannot be achieved if potassium deficiency is detected; sometimes measures to eliminate the deficiency are not economically justified. The best action is to eliminate potassium shortage in the identified areas to prevent deficiency in subsequent crops.

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Calcium deficiency

Calcium deficiency in corn plants can lead to complete yield loss. Calcium deficiency is relatively rare, usually on sandy soils during drought. More often, the deficiency is associated not with a lack of the element in the soil but with its unavailability to plants.

The development of calcium deficiency in corn is promoted by:

acidic sandy soils leached by abundant precipitation;
saline soils with high exchangeable sodium content;
rapidly drying light sandy soils;
soils with high soluble aluminum content and low exchangeable calcium level;
soils with high ammonium content;
strongly acidic peat soils and soils with low calcium content;
soils with acidity less than pH 6.5;
alkaline soils with pH above 8.5.

Symptoms of calcium deficiency

Plants are very stunted with distorted, torn, and ragged foliage; ears are small; tassels are distorted. Under acute calcium deficiency, corn plants stop growing and die before maturity.
Calcium is immobile in plants; under deficiency it is almost not mobilized from old leaves to young leaves.
Symptoms appear first on young leaves.
Deficiency begins to manifest as yellow or pale interveinal lesions on young leaves.
If the deficiency persists or intensifies, newly emerging leaves cannot unfold and acquire a curved shape (“bullwhip”).
As deficiency develops, holes appear in the leaf blade of new leaves. Torn and deformed leaves give the plant a ragged appearance.
Under acute deficiency, the tips of the youngest leaves stick together and do not separate from the whorl; plants acquire a “ladder-like” appearance.

Stages of calcium deficiency development

Stage I. In the early stages of deficiency, young leaves become pale green, then yellow or white damage appears in interveinal tissues. Damage from yellow to white increases, and the blade easily tears from these areas.

Stage II. If the deficiency persists and intensifies, the youngest leaves remain curled, forming a curved shape.

Stage III. As symptoms develop, holes appear in the blade of new leaves. Torn and deformed leaves give the plant a ragged appearance.

Stage IV. Under severe deficiency, leaf tips stick together, giving a “ladder-like” appearance.

Management of calcium deficiency

Management of calcium deficiency includes:

agrochemical soil analysis before planting to determine the soil’s need for liming or calcium;
application of recommended amounts of fertilizers containing calcium, for example, gypsum (calcium sulfate), calcium nitrate, or calcium chloride;
liming of acidic soils;
gypsum application on alkaline soils;
two foliar applications to crops with a 2% calcium sulfate suspension, calcium nitrate solution, or calcium chloride solution; the latter can be used at air temperature not above 30 °C;
increasing the soil’s water-holding capacity, primarily by increasing organic matter content;
on soils where calcium deficiency has been noted, it is recommended not to apply ammonium nitrogen fertilizers;
split application of nitrogen fertilizers to reduce their entry into plants in the initial phases of development;
ensuring sufficient soil moisture, including mulching.

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Magnesium deficiency

Magnesium deficiency can lead to a large yield shortfall, since plants develop small ears with small kernels.

The development of magnesium deficiency in corn is promoted by:

acidic sandy soils leached by heavy precipitation;
peat soils with low magnesium content;
soils with high calcium or potassium content;
soils formed on rocks with low magnesium content;
soils with acidity less than pH 6.5;
alkaline soils with pH above 8.5;
low cation exchange capacity, especially common on sandy and silty soils;
high content of potassium, ammonium, sodium, calcium, aluminum, and iron (II) cations;
low soil temperature;
high water permeability of soils with strong moistening.

Deficiency may appear depending on growing conditions and applied fertilizers (potassium and ammonium).

Symptoms of magnesium deficiency

Plants lag in growth, have a thin stem and pale green leaves; lower leaves are rusty brown. Ears and kernels are small.
Magnesium is mobile in plants, so under deficiency it is mobilized from old leaves to young leaves. Symptoms of magnesium deficiency appear first on old leaves.
Symptoms begin with the appearance of pale yellow interveinal chlorosis in the middle part of old leaves.
As symptoms progress, interveinal chlorosis spreads to the tip and base of the leaf, eventually covering the entire leaf. The youngest leaves usually remain unaffected.
If the deficiency persists and becomes stronger, symptoms move to the upper leaves, and rusty brown stripes appear on affected old leaves.
In later stages, interveinal tissue dies and looks like whitish or brown necrotic stripes. Affected old leaves eventually dry out and die.

Stages of magnesium deficiency development

Stage I. In the early stage of deficiency, leaves acquire a pale green color; pale yellow interveinal chlorosis develops on old leaves.

Stage II. If the deficiency persists and intensifies, rusty brown stripes appear on old leaves.

Stage III. As symptoms progress, interveinal tissue dies, acquiring the appearance of whitish-brown necrotic stripes on affected leaves.

Stage IV. Under conditions of severe deficiency, old leaves die.

Management of magnesium deficiency

Management of magnesium deficiency includes:

agrochemical soil analysis before planting to determine the content of soluble and exchangeable forms of magnesium in the soil;
application of recommended amounts of magnesium fertilizers, for example, magnesium sulfate or magnesium chloride;
if deficiency is detected in corn crops, application of soluble magnesium salts with irrigation water. Spraying is ineffective because replenishing plant magnesium requirements requires repeated spraying at short intervals;
acidic soils are limed with dolomite flour several months before planting;
regulation of the acidity of acidic or alkaline soils to ensure normal magnesium uptake by plants.

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Sulfur deficiency

Sulfur deficiency in corn plants leads to reduced nitrogen efficiency. There are approximately 15 parts of nitrogen per one part of sulfur.

The development of sulfur deficiency in corn is promoted by:

soils with low organic matter content;
light sandy soils by texture, leached as a result of abundant precipitation or irrigation;
soil depletion as a result of intensive crop cultivation;
soils formed on rocks with low sulfur content;
acidic soils with pH less than 6.0;
minimum tillage or absence of tillage (no-till).

Sulfur deficiency in corn crops often appears in localized patches or strips.

The two main factors leading to the development of sulfur starvation in corn are leaching of mobile sulfur compounds from the root zone and delayed root system development, for example, minimum tillage, in which the root zone is poorly mixed, warms slowly, and becomes compacted.

Symptoms of sulfur deficiency

Leaves have a color from pale green to yellow. Due to lack of energy, plants form small ears with few kernels.
With a slight sulfur deficiency in the young period, plants become pale green or yellow-green. At this stage, symptoms of sulfur deficiency are often confused with symptoms of nitrogen deficiency.
The distinction between sulfur deficiency and nitrogen deficiency is that under sulfur deficiency old leaves have a darker green color and young leaves are pale, whereas under nitrogen deficiency old leaves are paler and young leaves are dark green.
Sulfur deficiency, even if severe, does not lead to necrosis or leaf death. Change in leaf color is the only sign of sulfur deficiency.
Sulfur is immobile in corn plants and is almost not mobilized from old leaves to young leaves. Therefore, deficiency symptoms appear first on young leaves.
Symptoms appear as uniform pale green to pale yellow chlorosis on the blades of young leaves. The youngest leaves are the lightest.
Under conditions of severe deficiency, a red-purple color sometimes develops on affected young leaves in the form of bleeding over the yellow color.

Stages of sulfur deficiency development

Stage I. With mild deficiency in the initial phases of development, all leaves become pale green to yellow; older leaves remain relatively darker.

Stage II. As symptoms develop, young leaves become pale yellow, while older leaves are green and normal.

Stage III. If the deficiency persists and intensifies, symptoms move down the plant.

Stage IV. Under conditions of severe deficiency, a red-purple color sometimes develops on affected young leaves in the form of bleeding over the yellow color.

Management of sulfur deficiency

Management of sulfur deficiency includes:

agrochemical soil analysis before planting to determine the content of available sulfur forms in the soil (soluble sulfate ions);
application of recommended amounts (taking into account agrochemical analysis) of sulfur fertilizers, for example, elemental sulfur or gypsum;
if sulfur deficiency is detected in crops, ammonium sulfate, magnesium sulfate, or potassium sulfate is applied with irrigation water or by surface application followed by precipitation; in addition to sulfur fertilizers, it is advisable to also apply nitrogen fertilizers;
acidic soils are limed.

Sulfur deficiency, with sufficient reserves in the soil, may decrease as the plant root system develops, since this element is usually more available in deeper soil layers. When sulfur deficiency is corrected, if it appeared in a mild form and measures were taken before the 5th leaf stage, planned yield levels may be preserved. However, severe or prolonged deficiency can cause loss of up to 75% of the yield.

Elemental sulfur is recommended for long-term correction of sulfur deficiency, but it is not used to correct it in crops because it oxidizes slowly to the plant-available form, sulfates. To correct deficiency in crops, ammonium thiosulfate can be applied to the soil, but contact with leaves should be avoided.

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Iron deficiency

The development of iron deficiency in corn is promoted by:

sandy soils with low iron content;
calcareous soils in which iron availability sharply decreases;
peat soils in which iron is bound by organic matter, reducing its availability in the soil solution;
acidic soils in which, despite high iron availability, high concentrations of soluble zinc, manganese, copper, or nickel hinder iron uptake by plants;
waterlogged soils;
alkaline soils with pH above 7.5.

Symptoms of iron deficiency

Leaves become yellow; under severe deficiency, leaf auricles almost do not develop.
Iron is immobile in plants, so symptoms appear first and more intensively on young leaves. Older leaves remain normal.
With mild deficiency or in the early stage, interveinal tissues of the uppermost young leaves become pale green or pale yellow.
If the deficiency persists or intensifies, bright pale yellow chlorosis develops between the leaf veins, as a result of which the veins become green and noticeable. Such interveinal chlorosis of the upper leaves is a specific symptom of iron deficiency in corn.
As symptoms develop, the noticeable green veins also disappear and become light green or pale yellow. Under severe deficiency, the entire leaf becomes snow-white.

Stages of iron deficiency development

Stage I. Temporary fading of interveinal tissues with noticeable green veins develops on the uppermost leaves of the plant.

Stage II. Interveinal tissues of the affected leaf acquire a bright pale yellow color with pronounced green veins, called “interveinal chlorosis,” which spreads uniformly along the entire length of the leaf.

Stage III. As deficiency develops, the pronounced green veins also disappear and become light green to pale yellow.

Stage IV. Under severe deficiency, the entire leaf becomes snow-white.

Management of iron deficiency

Management of iron deficiency includes:

agrochemical soil analysis before planting to determine the content of available iron forms in the soil;
gypsum application or other methods of restoring alkaline soils;
application of soluble iron salts, for example, iron sulfate or iron (II) chloride; however, these forms quickly convert to forms unavailable to plants. Application of organic iron forms (chelates) at 10 kg/ha is more preferable; on neutral soils, FeHEDTA and FeDTPA are recommended; on acidic soils, FeEDTA; on alkaline soils, FeEDDHA;
if iron deficiency is detected in crops, plants are sprayed with a 0.5–1.0% solution of organic iron forms (chelates) or soluble iron salts, with 2–3 sprays at an interval of 10–15 days.

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Manganese deficiency

Corn plants have a medium requirement for manganese.

The development of manganese deficiency in corn is promoted by:

light sandy soils leached as a result of heavy rains or excessive irrigation;
limed and alkaline soils in which manganese solubility sharply decreases;
soils with high organic matter content;
excessive application of lime fertilizers, especially under minimum tillage;
waterlogged peat soils in which manganese is bound by organic matter into forms unavailable to plants;
soils formed on rocks with low manganese content;
acidic soils with pH less than 5.0;
alkaline soils with pH more than 7.5.

Manganese deficiency can appear during drought and in wet cold soils when the root system is poorly developed.

Symptoms of manganese deficiency

Plants are stunted with a short stem and leaves from pale green to yellow. Ears are small with smaller kernels.
Tassels develop poorly, anther development is delayed. Pollen viability decreases.
Manganese is partially mobile in corn plants and is relatively difficult to mobilize from old to younger leaves; however, under deficiency it is partially transferred from old leaves to young leaves.
Deficiency symptoms appear first on middle leaves and then spread to younger and older leaves. In the initial stages of deficiency, the youngest and oldest leaves remain normal.
With mild deficiency, fading of interveinal tissues occurs on middle leaves.
If the deficiency persists and becomes stronger, interveinal chlorosis develops on middle leaves along the entire length of the leaf.
As symptoms progress, “white spots” develop in the zones of interveinal chlorosis on affected leaves. The appearance of white spots is a specific symptom of manganese deficiency in corn.

Unlike magnesium deficiency, which appears on old leaves, manganese deficiency appears primarily on young leaves.

Manganese deficiency and iron deficiency often appear together. Iron deficiency in corn has clear boundaries of interveinal chlorosis on leaves, whereas under manganese deficiency these boundaries are more diffuse. Unlike zinc deficiency, which appears only on part of the leaf, manganese deficiency appears along its entire length.

Stages of manganese deficiency development

Stage I. With mild deficiency, fading of interveinal tissues develops on middle leaves.

Stage II. If the deficiency persists and intensifies, interveinal chlorosis develops on middle leaves along the entire length of the leaf blade.

Stage III. As symptoms progress, all chlorotic tissue dies and becomes white, resulting in white spots between the veins of affected leaves. The veins remain green and raised.

Stage IV. Under severe deficiency, white spots become brown, and affected leaves die.

Management of manganese deficiency

Management of manganese deficiency includes:

agrochemical soil analysis before planting to determine the content of available manganese forms in the soil;
gypsum application or other methods of restoring alkaline soils;
application of organic fertilizers long before planting;
application of soluble manganese salts, for example, manganese sulfate before planting; on sandy soils, annual application of manganese fertilizers may be required;
if deficiency is detected in crops, spraying with a 0.2–0.3% solution of manganese sulfate or chelates (ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid, lignosulfonate), or at 1.1–2.3 kg of manganese per ha. Considering that manganese does not move through the plant, several sprays may be required.

It is advisable to apply manganese fertilizers in rows at planting or to spray vegetative plants, since broadcast application to the soil involves a large proportion of manganese converting to forms unavailable to plants. The rate of manganese application in rows is 3.5–5.7 kg/ha.

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Manganese toxicity

Corn is usually resistant to manganese toxicity. Toxicity, in addition to excessive application of manganese fertilizers, can appear on:

acidic soils;
waterlogged soil, in which manganese oxides unavailable to plants are reduced to soluble salts.

Symptoms:

darkening of veins, usually on old leaves;
interveinal chlorosis or necrotic darkening of leaves;
since manganese uptake by plants is controlled by calcium pectate formation, symptoms of manganese toxicity are similar to symptoms of calcium deficiency.

Management of toxicity consists of liming acidic soils and maintaining acidity in the optimal range, and draining waterlogged soils.

Zinc deficiency

Corn is one of the best indicator plants for zinc deficiency. Yield decreases sharply with zinc deficiency.

The development of zinc deficiency in corn is promoted by:

leached sandy soils with low zinc content;
eroded soils with local exposure of parent rock, in which zinc content is usually much lower;
cool wet weather;
soils with low or very high organic matter content;
soils with excessive application of phosphorus fertilizers; phosphorus is an antagonist of zinc;
acidic soils with pH below 5.0;
alkaline soils with pH above 7.5.

Zinc deficiency, as a rule, appears unevenly in the field and is localized in nature.

Symptoms of zinc deficiency

Zinc deficiency can lead to delayed and irregular appearance of distorted tassels without anthers.
Deficiency delays internode elongation, as a result of which leaves twist together at the top of the plant, forming a fan-like appearance.
Deficiency symptoms appear within 2 weeks after emergence.
Since zinc is poorly mobilized in plants, symptoms develop first on young leaves; old leaves remain green.
White or yellow stripes or bands of bleached leaf tissue appear on each side of the midrib, starting from the leaf base. The middle stripe and leaf edges remain green. This is a specific symptom of zinc deficiency in corn.
Under conditions of acute deficiency, affected tissue eventually dies and becomes pale gray, leaving the middle and edges green.

Stages of zinc deficiency development

Stage I. Mild zinc deficiency may appear as an interveinal stripe on young leaves. Unlike manganese and iron deficiency, in which the interveinal stripe runs along the entire length of the leaf, in zinc deficiency the stripes are mainly located in the half of the leaf closer to its base.

Stage II. If the deficiency persists and intensifies, the youngest leaves become pale green; stripes from white to yellow appear between the midrib and the leaf edge closer to the base.

Stage III. Under conditions of severe deficiency, affected tissue dies and becomes pale gray.

Management of zinc deficiency

Management of zinc deficiency includes:

agrochemical soil analysis before planting to determine the content of available zinc forms in the soil; agrochemical analysis for zinc is considered one of the most reliable among all micronutrients;
gypsum application or other methods of restoring alkaline soils or liming acidic soils;
application of organic fertilizers long before planting;
application of 25–30 kg/ha zinc sulfate or 10 kg/ha zinc chelate once every 2 years on soils with zinc deficiency;
zinc fertilizers are not applied simultaneously with phosphorus fertilizers;
if zinc deficiency is detected in corn crops, spraying with a 0.5% zinc salt solution or 0.25% zinc sulfate is carried out.

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Boron deficiency

Boron deficiency in corn plants disrupts normal pollination and fruiting, and affects plant and root system growth.

The development of boron deficiency in corn is promoted by:

drought or low soil moisture, which reduces boron uptake by plants;
soils formed on rocks with low boron content, for example, acidic igneous rocks or freshwater deposits;
sandy soils leached by abundant precipitation or excessive irrigation;
alkaline soils with excess lime;
excessively limed soils with a disturbed calcium-boron balance;
soils with low organic matter content;
acidic soils with pH below 5.0;
alkaline soils with pH from 7.5 to 9.0.

Symptoms of boron deficiency

Plants lag in growth, have a tough stem and pale green leaves. Ears are small and curved. Boron deficiency delays pollen tube growth, resulting in sterile ears or ears with few kernels.
Boron is immobile in plants; under deficiency it is not mobilized from old leaves to young leaves. Deficiency symptoms appear first and are more pronounced on young leaves. Old leaves remain green and healthy.
Symptoms appear on new leaves, which become pale green, short, and straight, and break easily when bent.
Affected leaves do not unfold completely, and the edges lose firmness.
If the deficiency persists and intensifies, wrinkling appears on affected leaves.
Under conditions of severe deficiency, watery and transparent stripes appear on affected leaves.

Symptoms of boron deficiency are similar to the initial stages of iron deficiency, zinc deficiency, calcium deficiency, or damage by false spider mite.

Stages of boron deficiency development

Stage I. Plants form pale green leaves with signs of limited growth.

Stage II. If the deficiency persists and intensifies, affected leaves do not unfold completely, and the edges lose firmness. Wrinkling appears on affected leaves.

Stage III. Under conditions of severe deficiency, watery or transparent stripes appear on affected leaves.

Management of boron deficiency

Management of boron deficiency includes:

agrochemical soil analysis before planting to determine the content of available boron forms in the soil;
application of recommended amounts of boron fertilizers taking into account the results of agrochemical analysis, for example, borax, boric acid, or chelated boron;
application of organic fertilizers long before planting;
foliar treatments with a 0.5% boric acid solution or chelated boron compounds are carried out 30–35 days after emergence or immediately after detection of deficiency symptoms.

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Molybdenum deficiency

The development of molybdenum deficiency in corn is promoted by:

soils formed on rocks with low molybdenum content;
acidic sandy soils;
soils with high iron content.

Symptoms of molybdenum deficiency

Leaves are pale green with interveinal and marginal chlorosis.
As deficiency intensifies, chlorosis transitions to necrosis.
Tassel is small.
Seed germination in ears at maturity.

Management of molybdenum deficiency

Management of molybdenum deficiency includes:

liming of acidic soils;
application of molybdenum fertilizers to the soil or as pre-sowing seed treatment, foliar feeding, for example, sodium molybdate, ammonium molybdate, molybdic acid, molybdenum trioxide, and molybdenum sulfide (in decreasing solubility), with application rates of 50–200 g of molybdenum per 1 ha.

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Innovative solutions

Scientists from the University of Minnesota (USA) have proposed a pilot project to detect nitrogen deficiency in corn using small unmanned aerial vehicles and computer vision. The aircraft collect high-resolution images of plants in the visual spectrum (RGB) at low altitude and, using built-in algorithms, automatically determine the nitrogen status of corn leaves. Image analysis algorithms eliminate the need for manual handling and analysis of leaf color and shape to determine potential nitrogen fertilizer consumption. The algorithm can detect deficiency even when unhealthy leaves are heavily obscured by healthy ones in images, and it also determines the density of affected leaves and provides recommendations on fertilizer application rates to correct the deficiency.

This relatively inexpensive solution makes it possible to effectively increase crop production in several ways: the method provides information about field condition, allows deficiency to be detected in the early stages, and gives recommendations on the amounts of nitrogen fertilizers needed and where to apply them. In addition, the technology prevents excess fertilizers from entering the environment and polluting water bodies.

Distinctive features of the technology compared with other methods of plant nutrition monitoring:

unlike manual diagnostics, it significantly facilitates the process of diagnosing deficiency;
unlike satellite imagery, the technology is applicable in almost any conditions and is significantly cheaper;
unlike spectroscopy used in precision agriculture, it allows precise identification of nitrogen deficiency from other diseases or deficiency manifestations (spectroscopy only estimates the proportion of leaves colored in certain colors);
the algorithm can determine the type and degree of nitrogen deficiency based on the number and density of leaves affected by changes in color and texture.

The development is being implemented by Sentera.

References

Prakash, K., Manoj, K.Sh. (2013). Nutrient Deficiencies in Field Crops: A Guide to Diagnosis and Treatment.