Plant Nutrition

Soil plant nutrition

For starters, let's talk about how most terrestrial plants obtain nutrients. And, if you guessed that these nutrients come from the soil, you guessed right! The majority of terrestrial plants obtain their nutrients and water from the soil by using their root systems.

To better understand this, let's review the organ system of vascular plants.

These plants have two organ systems: the shoot system and the root system.

• The shoot system comprises leaves, stems, flowers, and fruits.

• A plant's root system anchors the plant and absorbs water and nutrients.

Vascular plants have a vascular system made up of a collection of tissues whose job is to bring water and minerals up from the roots and distribute sugar from the leaves. The vascular tissue is made up of the xylem and phloem.

Plants have other important structures such as stems, leaves, and roots. The stems provide support to the plant and deliver nutrients from the soil to the leaves. It also brings sugars (ex. glucose) from the plant leaves to its roots. The leaves are the organs of the plants responsible for capturing sunlight for photosynthesis.

The roots are structures that collect nutrients and water from the soil. It also helps plants stay in the plant without being blown or washed away.

First, water from the soil (containing dissolved minerals) enters the roots via osmosis.

• The process of osmosis involves water molecules diffusing across a partially permeable membrane from a high-concentration region to a low-concentration region.

Then, water travels to the xylem tissue. Water molecules are able to climb the xylem tissue, traveling through the plant, and eventually evaporating from the leaf surface. This process in called transpiration.

Nutrients move from the source cell (where they are made, for example leaf cells that make sucrose) to the sink cell (where they are needed). They are transported through plants in the sieve tubes of the phloem tissue.

Autotrophic vs. heterotrophic nutrition in plants

Plant nutrition can be classified into two categories: autotrophic and heterotrophic nutrition.

• Autotrophic plants are those plants that are able to make their own food from simple inorganic raw materials.

• Heterotrophic plants are not able to synthesize their own organic nutrients from inorganic sources. Instead, they depend on external sources for food.

Micronutrients for plants

Soil contains different types of nutrients that are essential for plant health. These plant nutrients can be either macronutrients or micronutrients.

Macronutrients, as the name suggests, are those elements that plants require in relatively large amounts. There are nine macronutrients that you should be familiar with: carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur.

• Carbon (C) and Oxygen (O) are taken up from the atmosphere as carbon dioxide (CO₂) gas and oxygen (O₂) gas and absorbed through leaves.

• Hydrogen (H) can come from water (H₂O) taken up by roots, or as hydrogen ions (H⁺) in the soil.

• Nitrogen (N) is found in the soil as nitrate (NO₃^-) and ammonium (NH₄⁺).

• Potassium (K) is taken up by roots as potassium ions (K⁺).

• Calcium (Ca) is taken up by roots as calcium ions (Ca²⁺).

• Magnesium (Mg) is taken up by roots as magnesium ions (Mg²⁺).

• Phosphorus (P) is found in the soil mostly as hydrogen phosphate (H₂PO₄^-).

• Sulfur (S) is found and taken up by roots are sulfate ions (SO₄^2-).

Micronutrients, on the other hand, are those elements that are only required in small amounts by plants. These are molybdenum, iron, manganese, boron, zinc, copper, chlorine, nickel, and sodium.

• Molybdenum (Mo) is taken up by roots as molybdenate (MoO₄^2-).

• Iron (Fe) is found in the soil and take up by roots as Ferrous ions (Fe²⁺).

• Manganese (Mn) is taken up by the roots as manganese ions (Mn²⁺).

• Zinc (Zn) is taken up by the roots as zinc ions (Zn²⁺).

• Copper (Cu) is taken up by the roots as cupric ions (Cu²⁺).

Plant nutrition photosynthesis

Plants are able to perform photosynthesis, and this process occurs in the chloroplasts of leaves. Chloroplasts are photosynthetic organelles found in plants. Inside chloroplasts, we can find chlorophyll, a green pigment responsible for capturing light energy for photosynthesis.

Impact of plant nutrition on growth

Nutrient availability plays an important role in plant growth and health. Every plant has a different sufficiency range, and if nutrient levels are not within this range, that plant will have a decline in growth and health.

If a plant does not get sufficient amounts of a specific nutrient, it will develop a deficiency. Now, if a nutrient is found in excess, toxicity will happen, and plant growth will also decrease.

Nutrient deficiency in plants

When a plant experiences a shortage of certain nutrients due to poor soil quality, for example, then it will suffer from nutrient deficiency. The most common nutrient deficiencies that affect plants are nitrogen, phosphorus, and potassium deficiency.

If a plant has nitrogen deficiency, symptoms include the general yellowing of older leaves, while the rest of the plant looks light green. To prevent or overcome nitrogen deficiency, we can use fertilizers that contain ammonium, nitrate, or urea.

In the case of a phosphorus deficiency, the leaf tips look burnt, whereas the older leaves become reddish-purple or dark green. In this case, fertilizers containing phosphate or "bone" would help.

Now, if a plant suffers from potassium deficiency, the older leaves may wilt and look scorched. To prevent K deficiency, use fertilizers containing sulfates.