Initial nitrous oxide fluxes from a maize-legume cropping system in a soil of the derived savanna zone of Nigeria-effect of fertilizer and incorporated organic matter

Legume—maize crop rotations are used as a mechanism to reverse declining soil fertility in West Africa. However, such crop rotations exhibit a relatively low recovery of legume N. Temperate region studies partly attribute low N recovery to gaseous N losses, but this has not been established for most cropping systems in the moist tropical savannas. The effect of incorporating added organic residues and fertilizer application on gaseous N20 ?uxes was studied in a ?eld trial at the International Institute of Tropical Agriculture (IITA), Ibadan (7, °30'N, 3 °S4'E) in the derived savanna zone of Nigeria. Gaseous N2O ?uxes were obtained 1, 3, 5, 8, and 15 days after incorporation of organic residues using a vented closed chamber system. Fluxes were examined in relation to soil mineral N status and rainfall patterns. Fertilizer application and incorporation of Pueraria phaseoloides organic residue increased soil mineral N contents as well as gaseous NZO ?uxes. Over the 15-day period, the total NZO fluxes were in the range of 21-30 mg N m2 for P. phaseoloides and 12-15 mg N m2 for natural fallow. Fertilizer-derived NZO ?uxes were less than 1% of applied fertilizer N.