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In addition to the weather conditions, agronomic practices can have a major influence on maize crop yield and contamination with mycotoxins. In this work, the effect of different irrigation systems (flood vs. sprinkler irrigation), sprinkler irrigation management (low vs. high frequency, daytime vs. nighttime irrigation) and tillage practices (conventional tillage, no tillage with or without crop stover) on crop yield and the contamination with aflatoxins (AFs), fumonisins (FUM) and deoxynivalenol (DON) were evaluated in the maize grain from two experimental maize fields. No aflatoxins were detected in any of the samples analyzed. DON and FUM levels were significantly higher when the sprinkler irrigation was performed at nighttime (0.54 and 1.21 mg kg−1, respectively) as compared to daytime (0.38 and 0.45 mg kg−1). Likewise, DON and FUM were greater when irrigation frequency was low (0.61 and 1.09 mg kg−1, respectively) in comparison with high frequency (0.30 and 0.57 mg kg−1). DON concentrations were significantly higher in fields with sprinkler irrigation (0.53 mg kg−1) as compared to flood irrigation (0.19 mg kg−1), while the levels of FUM were very similar regardless of the maize irrigation system. Mycotoxin concentrations were not affected by the different soil tillage practices. This highlights the importance of implementing crop management practices to minimize the risk of mycotoxin contamination in maize.

Maize is a major irrigated crop in Mediterranean areas and its typical intensive management may impact soil nitrous oxide (N2O) emissions. In these irrigated continuous maize systems, the legumes incorporation as well as adjusted nitrogen (N) fertilization might be interesting strategies to reduce soil N2O emissions. The objective of this study was to assess the impact of cropping diversification and different N rates on soil N2O emissions in flooded irrigated maize under Mediterranean conditions. To achieve this, two cropping systems (maize monoculture system, MC; and pea -maize rotation, MP) and 3N rates (unfertilized, 0N; medium rate, MN; and high rate, HN) were evaluated in a field experiment established in NE Spain during 2 years (2019; 2020). During the studied period, the N rate had a significant effect on soil N2O emissions, with a non-linear positive response of cumulative soil N2O emissions to N rates. In both systems, quick and high increases of soil N2O fluxes were observed immediately after the N application reaching 55 and 100 mg N2O-N m−2 day−1 in MC and MP, respectively. Both years, the pea phase of the MP rotation showed greater cumulative N2O emissions than the fallow of MC. However, N2O losses in the maize phase were similar (2019) or even higher (2020) in MC than in MP. Moreover, in both seasons, the MN treatments showed lower yield-scaled N2O emissions and N emission factor than the HN treatments, being this last lower than 1% in all cases. The results obtained showed that in irrigated Mediterranean conditions the replacement of a fallow by a legume, together with an adjusted N fertilization are favourable strategies to mitigate soil N2O emissions in high-yielding maize systems.

[ES] El riego y el manejo del suelo son prácticas agrícolas que pueden afectar a los procesos de producción, consumo, transporte y emisión de gases de efecto invernadero (GEI) del suelo. Por tanto, resulta necesario evaluar y documentar el impacto de estas prácticas sobre las emisiones de estos GEI. El objetivo general de esta Tesis doctoral ha sido cuantificar el efecto del sistema de manejo del suelo y el sistema de riego y su gestión sobre la producción, transporte y emisión de GEI del suelo a la atmósfera en sistemas de monocultivo de maíz bajo condiciones mediterráneas. Para alcanzar este objetivo, entre los años 2015 y 2017 se realizaron dos ensayos de campo en la finca experimental de la Estación Experimental de Aula Dei (EEAD-CSIC) ubicada en la depresión central del Valle del Ebro., [EN] Irrigation and soil management are agricultural practices that can affect the processes of production, consumption, transport and emission of greenhouse gases (GHG) in soils. Therefore, it is necessary to assess the impact of those practices on soil GHG emissions. The general aim of this PhD Thesis was to quantify the effects of the soil management system and the irrigation system and its management on the production, transport and emission of soil GHG emissions in maize (Zea mays L.) monoculture systems under Mediterranean conditions. To achieve this objective, two field trials were conducted in 2015-2017 in the experimental farm of the Aula Dei Experimental Station (EEAD-CSIC) located in the central depression of the Ebro River Valley., [CA] El reg i el maneig del sòl són pràctiques agrícoles que poden afectar als processos de producció, consum, transport i emissió de gasos d’efecte hivernacle (GEH) del sòl. Per tant, resulta necessari avaluar i documentar l’impacte d’aquestes pràctiques sobre les emissions d’aquests GEH. L’objectiu general d’aquesta Tesi doctoral ha sigut el de quantificar l’efecte del sistema de maneig del sòl i el sistema de reg i la seva gestió sobre la producció, transport i emissió de GEH del sòl a l’atmosfera en sistemes de monocultiu de panís sota condicions mediterrànies. Per assolir aquest objectiu, entre els anys 2015 i 2017 es van realitzar dos assajos de campo a la finca experimental de la Estación Experimental de Aula Dei (EEAD-CSIC) ubicada a la depressió central de la vall del riu Ebre.

Irrigation as well as soil tillage management are considered two possible strategies to reduce carbon dioxide (CO2) and methane (CH4) emissions from the soil in Mediterranean agroecosystems. The objective of this work was to assess the impact of the irrigation system (i.e. flood, F; and sprinkler, S) and the soil tillage system (i.e. conventional tillage, CT; no-tillage maintaining the maize stover, NTr; and no-tillage removing the maize stover, NT) on CO2 and CH4 emissions from the soil during three growing seasons (2015, 2016 and 2017) and two fallow periods between growing seasons (15–16 fallow and 16–17 fallow) in a maize (Zea mays L.) monoculture system. Soil temperature and water-filled pore space (WFPS) had a great influence on daily soil CO2 fluxes but not on daily soil CH4 fluxes. In all tillage-irrigation treatments, daily soil CO2 fluxes showed an increase with soil temperature, being this increment greater when soil temperature was above 15 °C in coincidence with the maize plant growth. In contrast, soil WFPS differently affected daily soil CO2 fluxes depending on the irrigation system. Under S irrigation, daily soil CO2 fluxes increased with soil WFPS, whereas under F irrigation a threshold value of 60% WFPS was found, with a positive or negative effect on CO2 fluxes for values below or above this threshold value, respectively. Over the three maize growing seasons, CT-S presented the greatest cumulative soil CO2 emissions with a seasonal average value of 3.28 Mg CO2-C ha−1. In contrast, for the same period, NTr-S cumulative soil CO2 emissions were up to 42% lower than the CT-S cumulative soil CO2 emissions. Cumulative CH4 emissions were only affected by soil tillage during the 16–17 fallow period, resulting both NTr and NT in greater net CH4 uptake compared with CT. This work highlights the importance of irrigation and soil tillage systems as key agricultural practices to minimize soil CO2 and CH4 emissions under Mediterranean conditions.

In croplands, the adoption of certain management practices may increase soil organic carbon (SOC) levels. In this study, we evaluated the short-term impact of crop stover management and the interaction between crop stover and irrigation method on SOC change in a continuous maize (Zea mays L.) system in Spain. Four years after the beginning of the experiment, total SOC and C fractions (particulate organic matter carbon, POM-C; and mineral-associated organic matter carbon, Min-C) contents, SOC stocks and SOC stock changes were measured in four different soil layers (0−5, 5−10, 10−25 and 25−50 cm) in an experiment with two irrigation methods (sprinkler and flood) and three stover management systems (conventional tillage with all the stover incorporated, CT; no-tillage maintaining the stover, NTr; and no-tillage removing the stover, NT). Stover management resulted in significant differences in SOC and POM-C but not in Min-C. In particular, NT reduced SOC and POM-C contents compared with CT and NTr (about 10 and 60 %, respectively). After 4 years, SOC change was not affected by the interaction between stover management and irrigation. Concurrently, both CT and NT showed SOC losses, reaching 0.11 and 1.22 Mg ha−1 yr−1 in CT and NT, respectively. However, NTr showed SOC gains at a rate of 0.09 Mg ha−1 yr−1. Consequently, the removal of crop stover has been demonstrated as a detrimental strategy to store SOC in the short-term in irrigated continuous maize systems.

Irrigation and soil management can impact soil nitrous oxide (NO) emissions. Flood and sprinkler irrigation systems together with conventional tillage are the main practices used in the high yielding maize systems in Mediterranean Spain. The objective of this field work was to quantify the effect of the irrigation system (i.e., flood, F; and sprinkler, S) and the soil tillage system (i.e., conventional tillage, CT; no-tillage maintaining the maize stover, NTr; and no-tillage removing the maize stover, NT) on the NO emissions from the soil during 3 yr (2015, 2016, and 2017). S irrigation, with mean values of 1.35 kg NO-N ha yr throughout the 3 yr, obtained 42% lower NO emissions than F irrigation. On average of the three growing seasons, yield-scaled NO emissions by grain yield and by grain N uptake in F irrigation were two-fold higher than in S irrigation. Moreover, in one out of three growing seasons (2017), no-tillage systems (i.e., NTr and NT) showed greater yield-scaled NO emissions compared with CT. The higher maize grain yield with the S irrigation compared to F irrigation, as well as the lower NO emissions reported under S irrigation resulted in the reduction of the yield-scaled NO emissions. Our findings highlight the role of sprinkler irrigation decreasing NO emissions in comparison to flood irrigation in Mediterranean agroecosystems.

The work shows, through results from different long-term experiments and some insights on crop rotation performance in commercial farms, how the adoption of conservation tillage, rational use of N fertilizers, sowing date delay and crop diversification, as integrated cropping system approach, can make wheat-based production systems more sustainable under Mediterranean conditions.

• Maize monocropping is the main cropping system under irrigated conditions in Spain. • Typical management includes high N fertilizer rates and irrigation with the concomitant impact on soil greenhouse gas emissions (GHG). • This study evaluates the impact of alternative diversified cropping systems to maize monocropping and varying N fertilization rates on soil GHG emissions.

Irrigation management may influence soil greenhouse gas emissions (GHG). Solid-set sprinkler irrigation systems allow to modify the irrigation time and frequency. The objective of this study was to quantify the effect of two irrigation times (daytime, D; nighttime, N) and two irrigation frequencies (low, L; high, H) on soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions in a solid-set sprinkler-irrigated maize (Zea mays L.) field located in NE Spain during 2015 and 2016 growing seasons and the fallow period between growing seasons. Compared with D irrigation, N irrigation increased soil water content (0–5 cm) in both growing seasons. Irrigation management did not affect CH4 emissions and the soil acted as a sink of CH4. Cumulative CO2 emissions were affected by the measurement period (growing season vs fallow) with the greatest values in 2015 growing season, being 81 and 32% higher over the fallow period and over the 2016 growing season, respectively, due to the effect of the preceding crop, alfalfa, and a better soil moisture conditions for the microorganism activity. Similarly, cumulative N2O emissions showed the highest values in 2015, reporting values 90 and 51% greater than the fallow period and the 2016 growing season, respectively. Moreover, N irrigation increased cumulative N2O emissions by 29% compared with D irrigation, but irrigation frequency did not affect cumulative N2O emissions. Irrigation time did not affect cumulative N2O emissions scaled per grain yield or per N uptake because N irrigation increased maize yield by 11% compared with D irrigation. Due to the lack of differences in the scaled N2O emissions, N irrigation should be consider as an appropriate strategy to optimize grain yield without compromising soil GHG emissions per unit of grain yield in Mediterranean agroecosystems.