Seasonal changes in nitrification potential associated with application of N fertilizer and compost in maize systems of southwest Michigan

Nitrification potential is the maximum capacity of a soil’s population of nitrifying bacteria to transform NH4+-N to NO3−-N. Time of season and the effect of several management practices on nitrification potentials were measured via an amended slurry method, shaken for 24 h at 25 ◦C. Management strategies that reduce potential nitrification rates without limiting plant N uptake may increase the ratio of plant biomass to plant N content (PB:N), the aboveground net primary production (ANPP) per unit of N in ANPP, and decrease the amount of NO3− available for leaching, and/or conversion to N2O. Sites were located in Hickory Corners, MI, USA, on Haplic Luvisols. Management practices included: substitution of compost for N fertilizer, use of a rotation in place of continuous maize and the addition of cover crops. A previously tilled, successional grassland was used as a contrast to agricultural managements. Where N fertilizer was applied, nitrification potential increased in late May and again in late August–October. The seasonal pattern was similar but less pronounced where compost was applied. Nitrification rates were 4.2 times greater than that of the successional site when N fertilizer was applied. Use of N fertilizer increased nitrification potentials 1.5 times above treatments where compost was applied during 1998 and 1999 in the 6th and 7th years of the rotation. In some instances, nitrification potentials could be correlated with in situ NO3−-N measurements. Average PB:Ns in the fertilizer management were greater or equivalent to the successional grassland site. Compost increased PB:N above that of N fertilizer. Utilization of compost decreased nitrification potentials, maintained yields, and increased PB:N. The crop N content was lower when compost was applied. Thus, grain and stover quality may be lowered and need to be monitored. © 2003 Elsevier Science B.V. All rights reserved.