Antonio Vallejo

Background and aims: Crop residue retention and cover cropping are key strategies in conservation agriculture, but their effects on nitrogen (N) cycling and nitrous oxide (N ₂ O) emissions, particularly in semiarid croplands, remain underexplored. This study aimed to evaluate the N dynamics and N ₂ O sources in an irrigated cover crop-maize rotation in central Spain by conducting a ¹⁵ N tracing experiment. Methods: ¹⁵ N-labeled maize ( Zea mays L.) residues were incorporated into the soil, followed by vetch ( Vicia faba L.), barley ( Hordeum vulgare L.) cover crops, or bare fallow. A subsequent maize crop was fertilized with 210 kg N ha ⁻¹ as ammonium nitrate (AN) or ¹⁵ N-labeled AN ( ¹⁵ NH ₄ NO ₃ , ¹⁵ AN//NH ₄ ¹⁵ NO ₃ , A ¹⁵ N) in the microplots receiving ¹⁵ N-enriched or unlabeled maize residues, respectively. Results: Cumulative N ₂ O emissions were 47% higher under vetch than under barley. Average N ₂ O emission factors were 0.05% for ¹⁵ N-labeled residues and 0.23% for fertilizer. Most N ₂ O originated from ¹⁵ AN (42%–61%), followed by endogenous sources (i.e., mineralization of organic N from soil or crop residues, 19%–42%) and A ¹⁵ N (9%–18%). Maize recovered 7.7% of residue N, with no differences between cover cropping treatments. Plant uptake from A ¹⁵ N was 2.3 times higher than from ¹⁵ AN. Across barley, vetch, and fallow, total N recovery averaged 33% in plants and 22% in soil. Barley cover cropping improved fertilizer N recovery in maize by 57% ( P < 0.05) compared with fallow. Conclusion: These findings highlight the role of cereal cover crops and the regulation of ammonium oxidation-based processes in enhancing N use efficiency and reducing fertilizer-derived N ₂ O emissions in semiarid agro-ecosystems.

Studies of the impact of nitrification inhibitors (NIs), specifically DMPP and DMPSA, on N₂O emissions during “hot moments” have produced conflicting results regarding their effectiveness after rewetting. This study aimed to clarify the effectiveness of NIs in reducing N₂O emissions by assessing residual DMP concentration and its influence on ammonia-oxidizing bacteria (AOB) in two pot experiments using calcareous (Soil C, Calcic Haploxerept) and acidic soils (Soil A, Dystric Xerochrepts). Fertilizer treatments included urea (U), DMPP, and DMPSA. The experiments were divided into Phase I (water application to dry period, 44 days) and Phase II (rewetting from days 101 to 121). In both phases for Soil C, total N₂O emissions were reduced by 88% and 90% for DMPP and DMPSA, respectively, compared with U alone. While in Phase I, the efficacy of NIs was linked to the regulation of AOB populations, in Phase II this group was not affected by NIs, suggesting that nitrification may not be the predominant process after rewetting. In Soil A, higher concentrations of DMP from DMPP were maintained compared to Soil C at the end of each phase. Despite this, NIs had no significant effect due to low nitrification rates and limited amoA gene abundance, indicating unfavorable conditions for nitrifiers. The study highlights the need to optimize NIs to reduce N₂O emissions and improve nitrogen efficiency, while understanding their interactions with the soil. This knowledge is necessary in order to design fertilization strategies that improve the sustainability of agriculture under climate change.

OpenToolFlux 1.0 is an open-source software designed to estimate soil gas fluxes from gas concentration time-series data generated by automatic chamber systems. This paper describes the physical equipment used as well as the software design and workflow. The software is a command-line application that imports tabular time-series data from the analyzer following the instructions specified in a configuration file by the user, performs configurable data-cleaning operations, and outputs a data file with volumetric flux estimates as well as diagnostic plots. The software can be configured according to the specifics of the physical equipment and experimental setups, and it is, therefore, applicable to a wide range of studies.

OpenToolFlux is an open-source software to estimate soil gas fluxes from gas concentration time-series data generated by automatic chamber systems. This paper describes the physical equipment used as well as software design and workflow. The software is a command-line application that imports tabular time-series data from the analyzer following the instructions specified in a configuration file by the user, performs configurable data-cleaning operations, and outputs a data file with volumetric flux estimates as well as diagnostic plots. The software can be configured according to the specifics of physical equipment and experimental setup and is therefore applicable in a wide range of studies.

Worldwide, Mediterranean cropping systems face the complex challenge of producing enough high-quality food while preserving the quantity and quality of scarce water for people and agriculture in the context of climate change. While good management of nitrogen (N) is paramount to achieving this objective, the efficient strategies developed for temperate systems are often not adapted to the specificities of Mediterranean systems. In this work, we combine original data with a thorough literature review to highlight the most relevant drivers of N dynamics in these semi-arid systems. To do so, we provide an analysis at nested scales combining a bottom-up approach from the field scale, with a top-down approach considering the agro-food system where cropping systems are inserted. We analyze the structural changes in the agro-food systems affecting total N entering the territory, the contrasting response of yields to N availability under rainfed and irrigated conditions in a precipitation gradient, the interaction between N management and climate change adaptation, the main drivers affecting the release of Nr compounds (nitrate, ammonia, nitric oxide and nitrous oxide) compared with temperate systems and finally, the behavior of N once exported to highly regulated river networks. We conclude that sustainable N management in Mediterranean cropping systems requires the specific adaptation of practices to particular local agro-environmental characteristics with special emphasis on water availability for rainfed and irrigated systems. This approach should also include a systemic analysis of N input into the territory that is driven by the configuration of the agro-food system.

Selection and management of synthetic nitrogen (N) fertilizers, including nitrification inhibitors, is considered an effective strategy to mitigate N oxide emissions, but depends strongly on soil characteristics and climatic conditions. We evaluated the effect of the use of a nitrification inhibitor (2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA)) or splitting calcium ammonium nitrate (CAN) on the N oxides and CH₄ emissions, yield, N use efficiency (NUE) and bread-making quality in a winter wheat (Triticum aestivum L.) crop. During a typical rainfall cropping season, neither splitting CAN nor using DMPSA reduced significantly the area-scaled or yield-scaled emissions in comparison to a single application of CAN without inhibitors. This could be explained by the low emissions in CAN amended plots. Conversely, in the subsequent extremely dry cropping season, higher N oxide peaks occurred after soil rewetting and the effectiveness of DMPSA was significant in these conditions (e.g. 83% mitigation for NO). No improvement in the NUE, yield or bread-making quality was achieved with a split application or DMPSA added to the fertilizer. Under the conditions of the study, splitting CAN should not be recommended from a yield-scaled emissions viewpoint, while the use of DMPSA may be encouraged due to large variability in the amount and distribution of rainfall.