Like all living organisms, plants require organic and inorganic nutrients to survive, reproduce, grow and maintain homeostasis. To identify nutrients that are essential for plant functioning, researchers have leveraged a technique called hydroponics. In hydroponic culture systems, plants are grown—without soil—in water-based solutions containing nutrients. At least 17 nutrients have been identified as essential elements required by plants. Plants acquire these elements from the atmosphere, the soil in which they are rooted, and water.

Nine of these essential nutrients—collectively called macronutrients—are needed by plants in more significant amounts. The macronutrients include carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium, magnesium, and potassium. Critical plant compounds, such as water, proteins, nucleic acids, and carbohydrates, contain macronutrients. Macronutrients also regulate cellular processes. For example, potassium regulates the opening and closing of stomata for gas exchange.

Plants need micronutrients in smaller amounts. These include chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum. Many micronutrients function as cofactors, which enable the activity of enzymes. Therefore, without micronutrients, plants are unable to perform critical functions.

A plant experiencing an essential nutrient deficiency may display symptoms, such as drying and yellowing leaves. Old and young leaves are susceptible to distinct nutrient deficiencies. For example, the younger leaves of a plant are often more affected by iron deficiency than the older leaves.

The effective treatment of nutrient deficiencies in plants is an integral part of agricultural and environmental practices. For example, optical sensors are used to measure the nitrogen content in soil. Nitrogen is critical for plants, but the excessive use of nitrogen-containing fertilizers (i.e., maintaining soil nitrogen levels that exceed what the plants can absorb) negatively influences ecosystem function and may contribute to global warming.