Nitrous oxide and methane emissions from a surface drip-irrigated system combined with fertilizer management

Drip-fertigated systems have variable distributions of water and nutrients in the soil, which influence soil microbial activity. Because there is a lack of data on greenhouse gas (GHG) fluxes for these systems, a field experiment comparing drip irrigation systems (fertigated and non-fertigated) was carried out in a melon crop. For the fertigated treatment, nitrogen (N) as NH4NO3 was dissolved in irrigation water and split into six applications (Fertigation treatment). In the non-fertigated soil (ANS treatment), granular NH4NO3 was incorporated homogeneously into the upper part of soil surface at planting. A control treatment without N fertilizer was also included. In order to evaluate the pattern of nitrous oxide (N2O) and methane (CH4), measurements were made at six different distances from the irrigation distributor point (dripper). An additional field experiment with N-15-labelled N fertilizer was carried out in parallel, with the aim of evaluating the contribution of nitrification and denitrification to the total N2O flux. Two different sources of N-15 were applied: (NH4NO3)-N-15 (20 at% excess N-15) ((NH4+)-N-15 treatment, TR1) and (NH4NO3)-N-15 (20 at% excess(15)N) ((NO3-)-N-15 treatment, TR2). Results indicated that both treatments (ANS and Fertigation) had small emission fluxes of N2O (< 0.1% of N applied). However, Fertigation produced larger emissions (175.3 g N2O-N ha(-1)) than ANS (90.1 g N2O N ha(-1)), with the pattern of N2O emission being strongly influenced by nitrification in both systems. Denitrification also contributed to emissions of (N2O)-N-15 but mainly on the day after fertilizer application in the Fertigation treatment. Methane fluxes were also affected by N fertilizer, with a decrease in the sink effect for CH4 when NH4+ was present in the soil.