2,000 - 3,000 mg N/m^2/yr
||Galloway et al., Nitrogen Cycles: Past, Present, and Future,
September 2004, Volume 70, Issue 2, pp 153-226 p.155 3rd paragraph
||Smil V. 1999. Nitrogen in crop production: an account of global flows. Global Biogeochem. Cycles 13: 647–662.
||"Non-Rhizobium N-fixing organisms associated with some
crops (e.g., cereals) and trees have ranges from 5X10^2 to 2X10^3 mgN/m^2,
while cyanobacteria associated with rice paddies and endophytic diazotrophs
associated with sugar cane can fix 2X10^3 to 3X10^3 mgN/m^2 and 5X10^3,
respectively (primary source)."