Plant nutrition

Plant nutrition is the study of the different chemicals and elements that plants need to grow and make seeds. Just like we need food to stay healthy, plants need certain elements to live their whole lives. There are seventeen important elements for plants, including carbon, oxygen, and hydrogen that they get from the air and water. Other elements, like nitrogen, come from the soil.

Plants need two main types of elements: macronutrients and micronutrients. Macronutrients, such as nitrogen, phosphorus, and potassium, are needed in larger amounts. Micronutrients, like iron and zinc, are needed in much smaller amounts but are still very important.

In nature, most soils give plants everything they need to grow well. But when farmers grow crops in the same soil for many years, the soil can lose some of these important elements. To help the plants grow better, farmers sometimes add special mixtures called fertilizers to the soil. This gives the plants the extra nutrients they need to grow big and strong.

History

People have always known that plants need nutrients from their environment, like water from the soil. Ancient thinkers like Aristotle wondered about these nutrients and how plants use them.

Plants get basic nutrients such as carbon, hydrogen, and oxygen from the air and water. In 1840, Justus von Liebig showed that plants also need nitrogen, potassium, and phosphorus to grow. He explained that a plant can't grow well if it lacks any important nutrient, known as Liebig's law of the minimum. Later, in 1939, scientists found that molybdenum is important for tomato plants.

Processes

Plants get the nutrients they need to grow from the soil through their roots and from the air through their leaves. Roots take in important elements by releasing hydrogen ions that help free nutrients from the soil. Leaves open tiny pores called stomata to take in carbon dioxide, which they use to make food through a process called photosynthesis.

Plants have special ways to absorb nutrients. Some nutrients move in by simply following a path from areas with more to areas with less, while others need help from special proteins in the plant's cells. Some nutrients even need energy to be taken in against their natural path. Nutrients travel inside the plant to where they are needed most, often going to younger leaves before older ones. Certain nutrients can move around the plant easily, while others stay in place.

Plants also work with tiny living things in the soil. Some bacteria help plants turn air into usable nitrogen, and fungi help plants reach more nutrients by expanding the effective size of their roots. Crops like alfalfa and soybeans have special bacteria that help them get nitrogen, while other plants like wheat and corn rely on nitrogen already in the soil or added by farmers.

Functions of nutrients

Plants need at least 17 different elements to grow well. Some of these, like nitrogen, phosphorus, and potassium, are needed in larger amounts and are called macronutrients. Others, like iron and zinc, are needed in smaller amounts and are called micronutrients. These nutrients must be available in the right amounts and ratios for plants to stay healthy.

Nitrogen is important for making proteins and chlorophyll, which helps plants make food through photosynthesis. Phosphorus helps with energy transfer and cell growth, while potassium helps with water regulation and enzyme activity. Other nutrients like sulfur, calcium, and magnesium help build plant structures and support important processes. Micronutrients such as iron, molybdenum, and boron are needed for enzyme functions and other plant processes, even though they are only needed in tiny amounts. Each nutrient has a special job in helping plants grow and stay healthy.

Mobility

Plants move nutrients in different ways. Nitrogen travels from roots to leaves through special parts called xylem and phloem. When a plant lacks nutrients like phosphorus or magnesium, the older leaves show problems first.

Some nutrients, like calcium and boron, don’t move easily in the plant. Calcium deficiency shows up in new growth because it comes from the xylem. Boron must go straight to growing parts, and sulfur can’t move from older leaves to new ones, so young leaves show problems first when sulfur is missing.

Nutrient deficiency

When plants don’t get the nutrients they need, they can grow more slowly, look strange, or even die. Sometimes this happens because they lack big nutrients like nitrogen or phosphorus. Other times, it's because they lack smaller nutrients like zinc or boron.

For example, without enough nitrogen, plants might grow slowly and their leaves can turn yellow. Without phosphorus, leaves might stay a very dark green or turn red. Potassium helps keep plants strong and healthy. Without it, leaves might brown and die. Micronutrients like zinc and boron are also important. If plants don’t get enough of them, leaves might look unusual or fruits might not grow properly.

Toxicity

See also: Abiotic stress § In plants, and Soil salinity

When there is too much boron in the soil, it can hurt most plants. Some small grain plants get harmed at levels between 10 to 50 parts per million, but crops like sugar beets and cucumbers can handle up to 200 parts per million. These conditions often happen in dry areas or where underground borax deposits or volcanic gases mix with water.

Availability and uptake

Plants need certain nutrients to grow well. Nitrogen is very important for plants. There is a lot of nitrogen in the air as N₂ gas, but plants cannot use it directly. Tiny living things called microorganisms, such as bacteria, help change nitrogen into forms plants can use, like ammonium (NH⁺₄) and nitrate (NO⁻₃). These bacteria live in the soil or work with plants.

Plants absorb nitrogen mostly through their roots. The amount of usable nitrogen changes with things like daylight, nighttime temperature, and other nutrients in the soil. This affects how much nitrogen the plant can use to grow.

Phosphorus is another important nutrient that plants often struggle to get. Plants can get more phosphorus help from a special relationship with fungi called mycorrhizae, which bring phosphorus to the plant.

Other nutrients like potassium, calcium, and boron also matter for plant health. The right balance of these nutrients helps plants grow best. The soil’s acidity, called soil pH, also affects how well plants can take up nutrients like boron.

Measurements

Scientists study plant nutrition by checking the minerals and tiny parts in plants. This helps us learn what plants need to grow. Long ago, a rule named "Liebig's law" said that plant growth depends on the thing that is hardest to find. Now, scientists use better math to see how nutrients help plants grow together.

New studies show that nutrients work together. They can change how plants take in other nutrients or how they work inside the plant. This helps us learn how to keep plants healthy.

Plant nutrition in agricultural systems

Fertilizers

Plants need certain nutrients to grow well. Sometimes, soil does not have enough of these nutrients, so farmers add special substances called fertilizers to help plants grow. For example, boron is a nutrient that can be hard for plants to keep in the soil, so it needs to be added carefully. Farmers test the soil first to decide how much boron to use.

Hydroponics

Hydroponics is a way to grow plants without using regular soil. Instead, plants are grown in water that contains all the nutrients they need. This method lets gardeners control exactly what the plants receive. One common mix used is called the Hoagland solution, which provides the right balance of nutrients for most plants. Air is also important, so an aerator is used to keep the water oxygenated. This helps the plants absorb nutrients properly.