Combination of drip irrigation and organic fertilizer for mitigating emissions of nitrogen oxides in semiarid climate

Fertilizer and irrigation management are two of the most important factors which directly influence nitrification and denitrification processes from agricultural soils and, therefore, emissions of nitrous oxide (N2O) and nitric oxide (NO). To date, the effect of combining organic fertilizer (applied before planting) with a drip irrigation system (DI) on the emissions of these nitrogen (N) oxides has not been evaluated. The different distribution and amount of water applied with this irrigation system should produce less favourable conditions for denitrification than other irrigation systems, such as furrow irrigation (FI), and this could be used to mitigate emissions of N2O, especially following organic fertilizer application. In order to test this hypothesis, a field experiment was carried out to compare the influence of FI and DI on N2O and NO emissions using digested pig slurry (DPS) as organic fertilizer during a melon crop (Cucumis melo L. cv. Sancho) season. Plots without any N fertilizer were used as a control (control). The irrigation system influenced the water distribution pattern, producing significantly higher ammonium-N (NH4+-N) and nitrate-N (NO3−-N) concentrations in the soil under DI than under FI. Moreover, the differences observed in water filled pore space (WFPS) and mineral N also favoured a different pattern of emissions of N oxides. Only one large pulse of N2O (106.9 mg N m−2 d−1) and NO (0.81 mg N m−2 d−1) were observed for FI after the first irrigation event while several pulses were observed for DI during the entire experimental period. As a consequence, nitrous oxide emissions were 75% and 28% lower from control and DPS, respectively under DI than under FI. In contrast, NO emissions were higher for DI on some sampling dates in both treatments, but without significant differences in the cumulative NO emissions between both irrigation systems. In conclusion, this work shows that combining drip irrigation with organic fertilizer for horticultural crops in semiarid climates could be a good management strategy for three reasons: it saves water; it re-uses organic residues and it mitigates N2O emissions.