Can soluble organic fertilizers and/or manure reach the agronomic and environmental performance of synthetic fertilizers in drip‐fertigated crops?

Abstract The substitution of synthetics by organic fertilizers, which is the current pillar of circular economy, has been broadly evaluated. However, varying results were obtained on nitrous oxide (N 2 O) and nitric oxide (NO) emissions as well as crop yields. Besides, in irrigated semi‐arid croplands, drip fertigation has been suggested to be an effective practice for mitigating N 2 O and NO emissions while maintaining or enhancing agronomic performance. However, the promising combination of drip fertigation and organic fertilization remains poorly studied. By setting up melon ( Cucumis melo L.) during 2022, and maize ( Zea mays L.) during 2023, we aimed to evaluate the effect of different combinations of nitrogen (N) fertilizers: control without N fertilization, 100% of the N rate as solid manure (100OrM), 50% of the N rate as solid manure and 50% as urea (50OrM–50Syn), 50% of the N rate as solid manure and 50% as soluble organic (50OrM–50OrS), 100% of the N rate as urea (100Syn) and 100% of the N rate as soluble organic (100OrS). Urea and soluble organic fertilizers were supplied via drip fertigation. N‐oxides (N 2 O and NO), methane (CH 4 ) and ecosystem respiration (CO 2 ) fluxes, mineral N (ammonium [NH 4 + ] and nitrate [NO 3 − ]), dissolved organic carbon (DOC) and crop parameters were analysed. As regards N 2 O, no differences were observed between treatments in melon crop, whereas in maize crop, the cumulative emissions were the highest in 100OrM, followed by 50OrM–50Syn. Regarding NO cumulative emissions, in the melon crop were significantly lower in 50OrM–50Syn and 50OrM–50OrS between 34%–54%, compared with 100OrM and 100Syn. In the maize crop, the highest cumulative NO emission was also detected in solid manure treatment. The agronomic response of melon to N fertilization was only detected for total soluble solids (with maximum values in the 100Syn treatment). The combination of solid manure and top‐dressing urea or soluble organic fertilizer prevented the penalties in N use efficiency, which were observed in 100Syn and 100OrS. Therefore, the combination of conventional solid manure at seeding and soluble organic fertilizer at dressing (applied by drip fertigation) was the most sustainable strategy from agronomic and environmental viewpoints in Mediterranean irrigated agroecosystems.