US EPA

1554353 

Book/Book Chapter 

Responses of crop plants to ammonium and nitrate N 

Li, SX; Wang, ZH; Stewart, BA 

2013 

Elsevier Academic Press 

San Diego, CA 

Advances in agronomy, vol. 118 

205-397 

English 

10.1016/B978-0-12-405942-9.00005-0 

WOS:000314252700005 

Nitrogen (N) is the most important, essential nutrient for all living organisms on earth; it is present in a number of complex organic molecules and plays extremely important roles in their activities. Ammonium N (NH4+-N) and nitrate N (NO3--N) are the main forms taken up by plants in addition to some organic N compounds. More than 90% soil N is in organic form. The intermediate products of complicated organic N substances can be absorbed by plants. Organic N nutrition affects plant product quality and plant metabolism. Organic N passes through the cell wall and arrives at the plasma membrane through the apoplast and cytoplast systems and, in addition to endocytosis, may get transported across the plasma membrane by an active (sugar/proton cotransport) or passive process. After uptake by plants, simple organic N compounds such as amino acids can be rapidly assimilated and transformed into other amino acids by transamination and deamination. The uptake of NH4+-N and NO3--N can be described by the Michaelis-Menten equation, and two parameters, the maximum absorption velocity (Vmax) and affinity constant or Michaelis constant (Km), have been used to measure the ability and efficiency of roots absorbing The two ions of crop plants. The uptake amounts of both NH4+-N and NO3--N at the seedling stage are well in agreement with their absorption kinetic parameters, particularly at low concentrations, but are not fully in agreement with the entire growing periods of crops. 

Sparks, DL 

Advances in Agronomy 

9780124059429