Organic matter and reducible iron control of ammonium production in submerged soils

Ammonium production is the key process for nitrogen (N) nutrition of wetlan d rice because N mineralization stops at ammonium production in submerged s oils. Earlier results emphasized the importance of organic matter in contro lling the release of ammonium in submerged soils. We studied the relationsh ips between mineralizable N and ammonium in soil solution and reducible iro n and organic C in 15 diverse West African soils. Mineralizable N released under anaerobic incubation at 30 degrees C for 2 weeks was significantly co rrelated to organic C (r=0.79) and iron extracted by EDTA (EDTA-Fe) (r=0.86 ) or ammonium oxalate (Amox-Fe) (r=0.75). Ammonium in soil solution at 2 we eks after flooding also was correlated to organic C (r=0.71), EDTA-Fe (r=0. 60) or Amox-Fe (r=0.60) although the correlation coefficients were lower th an those obtained with mineralizable N. Multiple regression analysis of min eralizable N and ammonium in solution with organic C and reducible Fe showe d that mineralizable N and ammonium in solution can be predicted from organ ic C and reducible iron status of the soils. The prediction of mineralizabl e N was better than the release of ammonium in soil solution. Our results u nderscore the importance of organic matter and reducible iron in controllin g the production of ammonium in wetland rice soils.