Plant nutrients and nutrient cycle

Plants need nutrients just like you need food to grow strong. Macronutrients are the big nutrients plants need in large amounts: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Micronutrients are needed in tiny amounts but are equally important—these include iron, zinc, manganese, boron, copper, and molybdenum.

Nitrogen helps leaves grow green and bushy, which is why Nigerian farmers apply chicken manure to their tomato farms. When plants lack nitrogen, leaves turn yellow from the bottom up. Without phosphorus, plants produce weak roots and poor flowers. Potassium deficiency causes brown spots on leaves.

Iron deficiency creates yellow leaves with green veins—common in waterlogged soils. Zinc deficiency stunts growth and reduces crop yields significantly.

Understanding these symptoms helps you diagnose crop problems early and recommend the right fertiliser treatment.

Soil nutrient availability means how easily plants can take up nutrients from the soil. Several factors control this process. Soil pH greatly affects nutrient uptake—acidic soils in southern Nigeria often lock up phosphorus, making it unavailable despite being present. Excess nutrients can also block absorption; too much potassium prevents calcium uptake. Leaching occurs when heavy rains wash nutrients downward, particularly in sandy soils common in northern regions. When farmers harvest crops without replenishing soil, nutrient removal depletes reserves permanently. Oxidation degrades organic matter containing nutrients, while burning vegetation destroys nitrogen stored in plant tissues.

Consider a farmer in Ibadan with degraded soil. Without adding manure or rotating crops, his continued harvesting removes more nutrients yearly than nature replaces. His yields eventually drop dramatically.

Soil loses nutrients when crops are harvested, so farmers must replace them to maintain soil fertility. Crop rotation involves planting different crops in sequence on the same land. For example, a farmer in Kaduna might plant maize one year, then legumes like beans the next year. Legumes restore nitrogen to soil naturally through their root nodules. Organic manuring adds nutrients by incorporating animal dung or compost into soil. Fallowing means leaving land unplanted for a season so soil recovers naturally. Liming adds calcium to acidic soils, improving nutrient availability. Cover-cropping involves planting nitrogen-fixing plants between main crops to enrich the soil. Chemical fertilizers provide quick nutrient replacement but can damage soil if overused. The best approach combines several methods rather than relying on one alone.

The nitrogen cycle shows how nitrogen moves between the air, soil, plants, and animals. Nitrogen gas from the atmosphere gets converted into usable forms by bacteria in the soil, allowing plants to absorb it through their roots. When plants and animals die, decomposers break them down, returning nitrogen to the soil. In Nigeria's cocoa farms, nitrogen-fixing bacteria in the soil help cocoa plants get the nitrogen they need to grow strong leaves and pods.

The carbon cycle involves carbon dioxide moving between the atmosphere and living things. Plants absorb carbon dioxide during photosynthesis to build their tissues, while animals eat plants and release carbon back through respiration. The phosphorus cycle works differently—phosphorus moves from rocks and soil into plants, then to animals, and back to soil through decomposition. The water cycle involves water moving between the atmosphere, soil, and organisms through evaporation, condensation, and precipitation.

Organic agriculture is a farming method that uses natural materials instead of synthetic chemicals to grow crops and raise animals. Farmers depend on compost, animal manure, crop rotation, and biological pest control rather than artificial fertilizers and pesticides. This approach maintains soil health by keeping it rich in organic matter and beneficial microorganisms.

In Nigeria, many farmers in areas like Osun State practice organic farming by composting kitchen waste and animal dung to fertilize their cassava and yam farms. This method produces healthier crops while protecting both the soil and water resources from chemical pollution. Organic farming also improves long-term soil fertility and reduces production costs for farmers who would otherwise buy expensive synthetic inputs. Additionally, consumers increasingly prefer organic produce because it contains fewer harmful chemicals, making it a profitable venture for Nigerian farmers.