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 take nutrients from their environment, like water from the soil, and move these nutrients through their tissues. Ancient thinkers like Aristotle wondered what these nutrients were and how plants absorbed and moved them inside.

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's growth can be limited if it lacks any necessary nutrient, known as Liebig's law of the minimum. Later, in 1939, scientists found that molybdenum is important for the growth of 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 play roles in building plant structures and supporting 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 plant parts called xylem and phloem. When a plant lacks certain nutrients like phosphorus or magnesium, the older leaves show problems first.

Some nutrients, like calcium and boron, don’t move easily within the plant. Calcium deficiency shows up in new growth because it mainly comes from the xylem. Boron must be supplied directly to growing parts, and sulfur can’t be moved 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 the problem is with a lack of big nutrients like nitrogen or phosphorus, and sometimes it’s with 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, and without it, leaves might brown and die. Micronutrients like zinc and boron are also important, and a lack of them can make leaves look unusual or stop fruits from growing properly.

Toxicity

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

When there is too much boron in the soil, it can harm most plants. For many small grain plants, harmful levels inside the plant are between 10 to 50 parts per million, while some crops like sugar beets and cucumbers can handle up to 200 parts per million. These harmful soil conditions usually 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, and nitrogen is one of the most important. There is a lot of nitrogen in the air as N₂ gas, but most plants cannot use it directly. Special tiny living things called microorganisms, such as bacteria, help change this nitrogen into forms plants can use, like ammonium (NH⁺₄) and nitrate (NO⁻₃). These bacteria can live freely in the soil or work together with plants.

Plants absorb nitrogen mostly through their roots. The amount of usable nitrogen changes depending on things like daylight length, temperature at night, and what other nutrients are present. This affects how much nitrogen the plant can use for growing.

Phosphorus is another important nutrient that plants struggle to get enough of, as it is often locked in soil. 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 looking at the minerals and tiny elements in plant tissues. This helps us understand what plants need to grow well. In the past, a rule called "Liebig's law" said that plant growth depends mostly on the scarcest resource available. Today, scientists use better math methods to understand how different nutrients work together to help plants grow.

New research shows that nutrients don't work alone. They can change how each other is taken up by the plant or how they act inside the plant. This helps us learn more about keeping 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. Too much boron can be washed away with extra water and special soil treatments.

Another important nutrient is selenium, which helps animals and humans stay healthy. When soil lacks selenium, farmers can add it to the soil to help plants and animals get enough.

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, created in 1933, 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. In some hydroponic systems, the plant roots are only partly in the water, allowing air to reach them while they get nutrients from a thin layer of water moving through the system.