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Nutrient Deficiencies In Plants: What Causes Them?

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Nutrient Deficiencies In Plants: What Causes Them?

The ear of corn on the right is nitrogen deficient.

USDA-ARS
Nutrient deficiencies in plants can lead to serious physiological problems. The outward signs of deficiencies can include leaf discoloration, spotting, wilting, and mistimed development of flowers or seeds. It's not true, however, that a nutrient deficiency is simply caused by lack of nutrient availability in the soil. Sometimes, the nutrient is present in plentiful amounts; yet, somehow, it cannot be taken up by the plant! How could this occur?

Soil Type

It is fairly clear that if you are looking to count the number of particles in a given volume, that there would be a much larger number of smaller particles than of larger particles. Therefore, a clay soil, which consists of very tiny particles, has many more particles in a given volume (say, a cubic foot) than does a sandy soil, which has comparatively large particles. Nutrients absorb onto soil particles; therefore, a pure clay soil will then be able hold more nutrients than will a pure sandy soil. Of course, soils of a pure type are fairly rare, and organic matter (also called humus, which consists of decomposed living material) also is able to hold a lot of nutrients. Basically, though, the more sand there is in a soil, the less able it is to hold nutrients, leading to a greater chance of deficiencies.

Soil pH

Have you ever wondered why gardeners and farmers add limestone (abbreviated as lime) to their growing areas? The soil pH - the measure of the acidity or alkalinity of a certain solution - affects the availability and uptake of some plant nutrients. For example, phosphorus - an extremely important plant nutrient needed for root initiation and growth - is available to plants optimally between pH 6 and 8.5. Micronutrients such as iron, manganese, and zinc are available only up to about pH 7.

Soil Moisture Content

Nutrients are not available to a plant until they are dissolved - or soluble - in water. The soil pH can also affect nutrient solubility in water. However, the presence of soil water can also have an adverse effect on nutrient availability. Some nutrients, such as nitrate (a nitrogen source), are not well retained by the soil and therefore can leach into groundwater if applied too heavily in a fertilizer and if too much water is in the soil. Because of the large particles and high amount of pore space in a sandy soil, nitrates tend to leach more heavily from a sand-based soil type.

Restricted air in a soil can also lead to nutrient deficiencies - think about a clay soil and how many particles it has packed together. Clays has low amounts of pore space and therefore low amounts of air. This can lead to delayed development of roots due to the physical stress as well as to the lack of nutrient uptake.

Other Nutrients

The presence of some important soil nutrients can affect the uptake of others. In acidic soils, high levels of aluminum and iron can "tie up" phosphorus and make it unavailable to plants. Phosphorus can also be affected by alkaline conditions, as calcium binds with phosphorus in high pH soils and makes them less soluble.

Soil Microorganisms

Microorganisms such as bacteria and fungi are often imperative for the survival of a plant. Mycorrhizal fungi live near plant roots and assist the plant in taking up nutrients. Mycorrhizae can modify nutrients such as fertilizer phosphorus to make the phosphorus more plant available. However, some fungicides can have an adverse effect on mycorrhizal proliferation in the soil, and therefore could lead to plant nutrient deficiencies.
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