Definition: Ability of the soil-plant system to limit the amount of inorganic N
accumulation in the rooting profile when N fertilization rates exceed that
required for maximum grain yields.

Nitrogen Buffering Mechanisms
(N in excess of that needed for maximum yield)

Plant NH₃ loss increases with higher rates of applied N
Increased forage N
Increased organic C
Increased grain protein
Increased denitrification
Increased volatilization (urea)

Conclusions:

• Nitrogen fertilization rates which significantly increased inorganic
  profile N accumulation, exceeded that required for maximum
  yields by more than 20 kg N ha^-1 in all experiments.
• Soil organic matter levels increased when N rates exceeded that
  required for maximum yield
• Use of fertilizer N at rates equal or less than that required to meet crop
  needs did not increase inorganic N accumulation
• Research results have documented increased

1. plant N loss
2. grain protein
3. denitrification
4. soil organic C
5. forage/straw N

when N rates exceed that required for maximum yield.

• Soil-plant inorganic N buffering is present in all production systems
  but is unlikely to be important when N rates continuously exceed twice that required

References:

Johnson, G.V., and W.R. Raun. 1995. Nitrate leaching in continuous winter wheat: use of a soil-plant buffering concept to account for fertilizer nitrogen. J. Prod. Agric. 8:486-491.

Raun, W.R., and G.V. Johnson. 1995. Soil-plant buffering of inorganic nitrogen in continuous winter wheat. Agron. J. 87:827-834.

Westerman, R.L, R.K. Boman, W.R. Raun and G.V. Johnson. 1994. Ammonium and nitrate nitrogen in soil profiles of long-term winter wheat fertilization experiments. Agron. J. 86:94-99.

Westfall, D.G., J.L. Havlin, G.W. Hergert and W.R. Raun. 1996. Nitrogen management in dryland cropping systems. J. Prod. Agric. 9:192-199.