Soil nitric and nitrous oxide emissions across a nitrogen fertilization gradient in root crops: A case study of carrot (Daucus carota) production in Mediterranean climate.

Insufficient knowledge about soil nitrous and nitric oxide (N2O and NO) emissions from vegetable production limits our ability to constrain their atmospheric budget. Carrots (Daucus carota) are a globally important, heavily managed and irrigated, high-value horticultural crop. Although intensively fertilized carrots may be an important hot-spot source of N2O and NO emissions, we have little information on the response of soil N2O emissions to fertilization and no information on the NO emissions response. To fill this knowledge gap, we conducted a replicated field experiment on mineral soil in the Negev Desert. We grew carrots with drip irrigation, applying five fertilization levels, ranging between 0 and 400 kg N ha-1. During one growth season we estimated responses of the soil N2O and NO emissions, partial crop N balance, and carrot yields to incremental fertilization levels. Carrot yield increased with increasing fertilization from 0 to 100 kg N ha-1 and exhibited no further response thereafter. Soil N2O and NO emissions were similar at all fertilization levels and did not differ significantly from those in the unfertilized control. The estimated N budget was negative for all fertilization levels. Carrots incorporated 30-140 kg N ha-1 into their belowground biomass and 120-285 kg N ha-1 into their aboveground biomass per season.