How does soil keep supplying plants with nutrients?

A plant removes water and mineral nutrients from the ground as it grows. Yet soil can support many seasons of growth when nutrients are replenished and the soil remains suitable for roots. Fertility is the soil's ability to supply nutrients a plant can use.

Some nutrients come from minerals as rock particles slowly change. Others arrive in dead roots, fallen leaves, manure or added fertilizers. Decomposers transform organic material, releasing nutrients into forms roots can take up. This takes time, and the speed depends on conditions such as moisture and temperature.

Particles of clay and well-decomposed organic matter can hold some nutrient ions rather than letting all of them wash away immediately. Roots draw from the watery solution between soil particles, and held nutrients can move into that solution. Nutrients are not all held equally well. Water moving through the soil may carry some away, while harvested crops remove others.

Fertile soil is therefore a changing store, not an endless supply. Roots also need enough air, water and space: nutrients alone cannot repair a badly compacted or waterlogged root zone. Keeping soil covered and returning suitable material can help maintain its functions. The next crop grows from a partnership between a mineral store, moving water and living organisms working below the surface.