Less than 1/3 of nitrogen fertiliser applied in a paddock ends up in the plants grown there; 70% is retained by some other form of life in the soil, volatilizes into the atmosphere runs off the paddock, or leaches down below the root zone with the movement of water through the soil. Synthetic nitrogen will often suppress the association soil microbes form with the plants.
Nitrogen fertilisers affect soil biology – if the entire amount of nitrogen that a crop needs is added to the soil in one application at planting time, it will often suppress the association soil microbes have with the plants.
Plants and soil microbes will use the applied nitrogen independent of each other instead of relying on each other, delaying many vital associations between them and due to this the plant-microbe relationship is bypassed early in the growing season i.e. the plants will use the rapidly available nitrogen from fertiliser instead of relying on soil organisms to supply it to them from naturally occurring sources in a long term, sustainable way.
Later, when the excess nitrogen is gone and with plants that have neglected to make suitable associations with their partners in the soil, the crop/pasture suffers as it spends time and energy trying the build an association with the soil microbes that shunned it earlier.
Eventually, the plant-microbe association will be created but often too late to meet the needs of the crop at a critical stage of growth.
The plants in effect become nitrogen addicts, dependant on an artificial supply of nitrogen in lieu of maintaining a healthy relationship with the rest of the soil community.
When any form of nitrogen is overapplied it can result in poor late-season crop performance and can result in some of the nitrogen leaching below the root zone before it can be acquired by soil microbes or plants.
For more in-depth information search the internet for:
- The impact of high nitrogen use in modern agriculture
- How can increasing soil health reduce plant nitrogen addiction