Nutrients
Plants need water, air, light, suitable temperature, and a minimum of sixteen nutrients to grow. These are:
- essential nutrients - C, H, O
- primary nutrients - N, P, K,
- secondary nutrients - Ca, Mg, S,
- micro-nutrients - Fe, Zn, B, Mo, Mn, Cl, Cu.
Plants get carbon, hydrogen and oxygen from the air and water. Other thirteen nutrients come from the soil and are absorbed through the plant’s roots. Since there is often a deficit in these nutrients in the soil, farmers and gardeners have resorted to the use of artificial fertilisers and manure to compensate (e.g. primary nutrients).
Environmental problems arise when not all fertiliser is taken up by the crop or incorporated in soil micro life. The main environmental problem associated with fertiliser use is the contamination of water with nitrates and phosphates. The nitrogen when converted to nitrate by bacteria in the soil can be leached into the groundwater or may be washed out of the soil surface into streams and rivers posing a threat to flora and fauna. High nitrate levels in drinking water are considered to be dangerous to human health.
Phosphorus is not readily washed out of the soil, but is bound to soil particles and moves together with them. Phosphorous can therefore be washed into surface waters together with the eroded soil. Phosphorus is not considered to be so dangerous for health, however it stimulates the grow of algae in slow moving water which leads to a decline in river eco-systems.
Application of nutrients in green houses is ajusted to the specific crop and to the water quality provided for the green house. Together with recycling of water this means that nutrients idealy don't leach from green houses.
Picture copyright: Landbrugsraadet
