Impact of tillage and N fertilization rate on soil N2O emissions in irrigated maize in a Mediterranean agroecosystem

In irrigated Mediterranean conditions there is a lack of knowledge about the best combination of tillage and N fertilization practices to reduce soil nitrous oxide (N2O) emissions while maintaining maize productivity. The aim of this work was to investigate the effects of different soil management practices and synthetic N fertilization rates on soil N2O emissions and their relationship with maize grain yield to determine the best management system to reduce yield-scaled N2O emissions (YSNE) in a semiarid area recently converted to irrigation under Mediterranean conditions. A long-term tillage and N rate field experiment established in 1996 under barley (Hordeum vulgare L.) rainfed conditions, was converted to irrigated maize (Zea mays L.) in 2015. After the transformation to irrigation, the field experiment maintained the same tillage treatments and N fertilization rates. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha−1) were compared during three years (2015-2017) in a randomized block design with three replications. Soil N2O emissions, water-filled pore space, soil temperature, mineral N content (as NH4+ and NO3−), denitrification potential and maize grain yield and above-ground N uptake were quantified. Moreover, the emission factor (EF) and YSNE were calculated. The results showed that the combination of NT and the highest rate of N fertilization led to greater N2O emissions. Furthermore, the lowest N2O fluxes were observed in CT when WFPS was below 40% and the highest N2O fluxes were seen in NT when WFPS was above 60% coinciding with the greatest denitrification potential. Cumulative N2O emissions in 2017 and 2015 followed the order 400 > 200 > 0 kg N ha−1, while in 2016, rate of 400 and 200 kg N ha−1 showed greater cumulative N2O emission compared to the control. Only RT showed differences between growing seasons on cumulative N2O emissions, with greater values in 2017 compared to 2015, and intermediate values in 2016. In all treatments, the N2O EF was much lower than the default IPCC emission factor (1%). NT and RT increased the grain production compared to CT which was affected by severe soil crusting causing water deficit. Likewise, N fertilizer treatments significantly affected the YSNE, increasing with increasing fertilizer N application rate in the first year of study. Our data show that the use of NT or RT does not lead to more yield-scaled N2O emissions than CT in Mediterranean agroecosystems recently converted to irrigation.This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784)

Is it feasible to reduce tillage and N use while improving maize yield in irrigated Mediterranean agroecosystems?

Mediterranean rainfed areas are transformed into irrigation to stabilize or increase crop yields. The gradual occupation of irrigation leads to an increase in nitrogen use and intensity of tillage. The aim of this work was to evaluate the combined impact of tillage systems and mineral N fertilization rates on maize grain yield, water and nitrogen use efficiencies (WUE and NUE) under Mediterranean irrigated conditions. The study was carried out in NE Spain during three maize growing seasons (i.e. years 2015, 2016 and 2017). A long-term (LTE) tillage and N rate field experiment established in 1996 under rainfed conditions was transformed into irrigation with maize (Zea mays L.) monoculture as cropping system in 2015. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha-1) were compared in a randomized block design with three replications. In 2015, an adjacent experiment (short-term experiment, STE) with the same layout was set up in an area previously managed under long-term rainfed NT for the last 21 years. Soil water (SWC) and nitrate (SNC) content were quantified. Maize above ground biomass and N uptake, grain yield and yield components, grain N were measured at harvest. The WUE for above ground biomass and yield (WUEB and WUEY, respectively) and NUE, as well as other N-related indexes (nitrogen harvest index, NHI; apparent nitrogen recovery efficiency, NAR) were calculated. In the long-term tillage and N fertilization combination (LTE), the reduction of tillage (NT and RT) led to greater grain yield when applying 200 and 400 kg N ha-1 compared to the use of the same rates under CT. Differently, in the sort-term experiment with preceding NT (STE), tillage systems did not influence grain yields, while N application led to greater yields than the control (0 kg N ha-1). In both situations (LTE and STE), NT and RT enhanced SWC before planting leading to greater crop growth compared to CT. The lack of available water under CT caused lower maize above-ground biomass, yield, and yield components in LTE and, therefore, lower WUEB and WUEY. In LTE, the use of long-term CT led to a significant accumulation of nitrate compared to NT. Differently, in the STE, SNC did not show differences between tillage systems. In the LTE, water and N were used more efficiently to produce above-ground biomass and grain yield in RT and NT. Our study shows that in Mediterranean agroecosystems transformed into irrigation the use of NT and RT with medium rates of N leads to greater maize yield, WUE and NUE than the traditional management based on CT with high rates of mineral N. In rainfed areas with long-term history of no-till, this soil management system can be successfully maintained if transformed into irrigation.We would like to thank the field and laboratory technicians Javier Bareche, Carlos Cortés, Barbara Jelcic and Silvia Martí. This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784)

Tillage and nitrogen fertilization in irrigated maize: key practices to reduce soil CO2 and CH4 emissions

In newly irrigated Mediterranean agroecosystems, the combined effect of tillage and N fertilization on soilcarbon dioxide (CO2) and methane (CH4)fluxes is at present poorly understood. The goal of this study was toquantify both soil CO2and CH4emissions as well as crop performance under different tillage systems and Nfertilization rates during three maize (Zea maysL.) growing seasons (2015-2017) in a semiarid area converted toirrigated. Three types of tillage (conventional tillage, CT, reduced tillage, RT, and no-tillage, NT) and threemineral N fertilization rates (0, 200, and 400 kg N ha−1) were compared in a randomized block design withthree replications. Weekly soil CO2and CH4emissions, soil temperature and gravimetric moisture were mea-sured. Moreover, maize above-ground biomass, grain yield, and above-ground C-inputs were quantified. Carbondioxide emissions ranged from 173 to 4378 mg CO2-C m-2d-1. No-tillage showed a greater mean soil CO2fluxthan CT when applying the highest rate of N (400 kg N ha-1). Although some emissions of CH4were observed, alltreatments acted as net CH4sinks during most of the experimental period. A linear multiple relationship betweensoil CO2fluxes and soil gravimetric moisture (0-5 cm depth) and temperature (10 cm depth) were found. In the2015 growing season, greater cumulative CO2emissions were found under NT and RT compared with CT, whilein 2016 N T showed the highest values compared to CT with intermediate values in RT. Differently, in 2017 nodifferences between tillage systems were found. When applying N fertilizer, NT and RT increased maize grainproduction and above-ground C-inputs compared to CT, since a severe soil crusting occurred in this last, whichcaused crop water deficit. The results suggest that tillage intensity and N fertilization rate reduction can increasemaize biomass production and yield which leads to greater C-input that returns to the soil.We would like to thank the field and laboratory technicians Carlos Cortés, Barbara Jelcic, Javier Bareche and Silvia Martí. This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784)

The role of sustainable agricultural practices to mitigate greenhouse gases and to sequester soil carbon under newly irrigated Mediterranean agroecosystems

Les àrees del secà mediterrànies es transformen en regadiu per estabilitzar o millorar el rendiment dels cultius. L’ocupació gradual del riego ha permès augmentar l’ús del nitrogen i la intensitat del laboreo. Per tant, l'objectiu principal d'aquest estudi va ser la d’evaluar els efectes dels diferents sistemes de conreu i les dosis de fertilitzants de N en les emissions de GEH (metà, CH4; diòxid de carboni, CO2, òxid nitrós, N2O) a l'atmosfera, així com, el segrest de C del sòl, l'estructura de la superfície del sòl i la productivitat del cultiu en una àrea recentment transformada a regadiu. Per aconseguir aquest objectiu, es va dur a terme un estudi en NE Espanya en un experiment de llarga durada (LTE) de conreu i dosis de fertilització N establert el 1996 sota la producció d'ordi (Hordeum vulgare L.) en secà, posteriorment, es transformar en monocultiu blat de moro (Zea mays L.) amb reg per aspersió en 2015. Aquest estudi es va realitzar durant tres campanyes consecutives de cultiu de blat de moro (és a dir, els anys 2015, 2016 i 2017). Es van comparar tres tipus de conreu (conreu convencional, CT, conreu reduït, RT, No conreu, NT) i tres dosis de fertilització mineral N (0, 200, 400 kg N ha-1) en un disseny de blocs a l'atzar amb tres repeticions. El 2015, es va crear un experiment adjacent (experiment a curt termini, STE) amb el mateix disseny que el LTE però amb una gestió anterior diferent basada en NT. En el LTE, les emissions de CO2, CH4 i N2O del sòl es van quantificar durant tres anys. A més, es va calcular el factor d'emissió de N2O (EF) i les emissions de N2O a escala de rendiment. També, es va calcular la taxa anual del segrest de SOC (ΔSOCrate) (0-40 cm de profunditat) per a cada tractament en tres períodes diferents (P1-, P2-, P3-) en condicions de secà (-R) i condicions de regadiu (-I) (P1-R, de 1996 a 2009; P2-R, de 2009 al 2015; P3-I, de 2015 a 2017). A més, en LTE i STE superfície del sòl (0-5 cm) es van mesurar macroagregats secs i estables en l’aigua i la seva concentració de C, així com altres fraccions del sòl (concentració total de SOC i concentració de C làbil). Així mateix, es va analitzar la resistència a la penetració en la superfície del sòl (PR) i la infiltració d'aigua durant la segona temporada de cultiu de blat de moro (és a dir, l'any 2016). Ingualment, en els dos camps experimentals, es va mesurar anualment la biomassa aèria, el rendiment de gra, els components de rendiment i l'eficiència d'ús d'aigua i nitrogen (WUE i NUE, respectivament). En els agroecosistemes Mediterranis recentment transformats a regadiu, una reducció de la dosi de fertilització N juntament amb una reducció en el conreu, és una estratègia òptima en termes de manteniment de la productivitat dels cultius. A més, la reducció del conreu millora l'estat estructural del sòl, per tal de proporcionar al sòl suficient resistència i assegurar un desenvolupament òptim dels cultius. Si bé la reducció del conreu genera més emissions de GEH del sòl a l'atmosfera, aquestes es compensen amb un major rendiment de blat de moro i segrest de SOC.Las áreas de secano Mediterráneas se transforman en regadio para estabilizar o aumentar el rendimiento de los cultivos. La ocupación gradual del riego lleva a un aumento en el uso de nitrógeno y la intensidad del laboreo. Por lo tanto, el objetivo principal de este estudio fue la evaluar los efectos de los diferentes sistemas de laboreo y las dosis de fertilizantes de N en las emisiones de GEI (metano, CH4; dióxido de carbono, CO2, óxido nitroso, N2O) a la atmósfera, así como, el secuestro de C del suelo, la estructura de la superficie del suelo y la productividad del cultivo en un área recientemente transformada a regadío. Para lograr ese objetivo, se llevó a cabo un estudio en NE España en un experimento de larga duración (LTE) de laboreo y dosis de fertilización N establecido en 1996 bajo la producción de cebada (Hordeum vulgare L.) en secano, posteriormente, se transformó en monocultivo maíz (Zea mays L.) con riego por aspersión en 2015. Este estudio se realizó durante tres campañas consecutivas de cultivo de maíz (es decir, los años 2015, 2016 y 2017). Se compararon tres tipos de laboreo (laboreo convencional, CT, laboreo reducido, RT, No laboreo, NT) y tres dosis de fertilización mineral N (0, 200, 400 kg N ha-1) en un diseño de bloques al azar con tres repeticiones. En 2015, se creó un experimento adyacente (experimento a corto plazo, STE) con el mismo diseño que el LTE pero con una gestión anterior diferente basada en NT. En el LTE, las emisiones de CO2, CH4 y N2O del suelo se cuantificaron durante tres años. Además, se calculó el factor de emisión de N2O (EF) y las emisiones de N2O a escala de rendimiento. También, se calculó la tasa anual de secuestro de SOC (∆SOCrate) (0-40 cm de profundidad) para cada tratamiento en tres periodos diferentes (P1-, P2-, P3-) en condiciones de secano (-R) y condiciones de regadio (-I) (P1-R, de 1996 a 2009; P2-R, de 2009 a 2015; P3-I, de 2015 a 2017). Además, en LTE y STE superficie del suelo (0-5 cm) se midieron macroagregados secos y estables en agua y su concentración de C, así como otras fracciones del suelo (concentración total de SOC y concentración de C lábil). Asimismo, se analizaron la resistencia a la penetración en la superficie del suelo (PR) y la infiltración de agua durante la segunda temporada de cultivo de maíz (es decir, el año 2016). Ingualmente, en ambos campos experimentales, se midió anualmente la biomasa aerea, el rendimiento de grano, los componentes de rendimiento y la eficiencia de uso de agua y nitrógeno (WUE y NUE, respectivamente). En los agroecosistemas Mediterráneos recientemente transformados a regadio, una reducción de la dosis de fertilización N junto con una reducción en el laboreo, es una estrategia óptima en términos de mantenimiento de la productividad de los cultivos. Además, la disminución del laboreo mejora el estado estructural del suelo, a fin de proporcionar al suelo suficiente resistencia y asegurar un desarrollo óptimo de los cultivos. Si bien la reducción del laboreo genera mayores emisiones de GEI del suelo a la atmósfera, estas se compensan con un mayor rendimiento de maíz y secuestro de SOC.Mediterranean rainfed areas are transformed into irrigation to stabilize or increase crop yields. The gradual occupation of irrigation leads to an increase in nitrogen use and intensity of tillage. Therefore, the main objective of this study was the identification of the effect of different tillage systems and N fertilizer rates on GHG emissions (methane, CH4; carbon dioxide, CO2; nitrous oxide, N2O) to the atmosphere, as well as, soil C sequestration, soil surface structure and crop productivity when converting rainfed lands to irrigated. In order to achieve that objective a study was carried out in NE Spain in a long-term (LTE) tillage and N rate field experiment established in 1996 under rainfed barley (Hordeum vulgare L.) conditions which was converted to irrigation with maize (Zea mays L.) monoculture as cropping system in 2015. This study was conducted during three consecutive maize growing seasons (i.e. years 2015, 2016, and 2017). Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha-1) were compared in a randomized block design with three replications. In 2015, an adjacent experiment (short-term experiment, STE) with the same layout as the LTE but with different previous management based on NT was set up. In the LTE, soil CO2, CH4 and N2O emissions were quantified during three years. Also, N2O emission factor (EF) and yield-scaled N2O emissions were determined. In addition, annual SOC sequestration rate (∆SOCrate) (0-40 cm depth) was calculated for each treatment in three different periods (P1-, P2-, P3-) under rainfed (-R) conditions and irrigated (-I) conditions (P1-R, from 1996 to 2009; P2-R, 2009 to 2015; P3-I, from 2015 to 2017). Moreover, in LTE and STE soil surface (0-5 cm) dry and water-stable macroaggregates and their C concentration, as well as other soil fractions (total SOC concentration and labile C concentration) were measured. Also soil surface penetration resistance (PR), and water infiltration were analyzed during the second maize growing season (i.e. year 2016). In addition, in both experimental fields, above ground biomass, maize grain yield, yield components and water and nitrogen use efficiency (WUE and NUE, respectively) were measured annually. In Mediterranean agroecosystems recently transformed to irrigated land, a reduction in N fertilization rate together with a reduction in tillage are optimum strategies in terms of maintenance of crop productivity. In addition, reductions of tillage improve the structural state of the soil, in order to provide the soil enough resilience and ensure an optimum development of crops. Although the reduction of tillage generates higher GHG emissions from the soil to the atmosphere, this is compensated by a greater maize yield and SOC sequestration

The role of sustainable agricultural practices to mitigate greenhouse gases and to sequester soil carbon under newly irrigated Mediterranean agroecosystems

Les àrees del secà mediterrànies es transformen en regadiu per estabilitzar o millorar el rendiment dels cultius. L’ocupació gradual del riego ha permès augmentar l’ús del nitrogen i la intensitat del laboreo. Per tant, l'objectiu principal d'aquest estudi va ser la d’evaluar els efectes dels diferents sistemes de conreu i les dosis de fertilitzants de N en les emissions de GEH (metà, CH4; diòxid de carboni, CO2, òxid nitrós, N2O) a l'atmosfera, així com, el segrest de C del sòl, l'estructura de la superfície del sòl i la productivitat del cultiu en una àrea recentment transformada a regadiu. Per aconseguir aquest objectiu, es va dur a terme un estudi en NE Espanya en un experiment de llarga durada (LTE) de conreu i dosis de fertilització N establert el 1996 sota la producció d'ordi (Hordeum vulgare L.) en secà, posteriorment, es transformar en monocultiu blat de moro (Zea mays L.) amb reg per aspersió en 2015. Aquest estudi es va realitzar durant tres campanyes consecutives de cultiu de blat de moro (és a dir, els anys 2015, 2016 i 2017). Es van comparar tres tipus de conreu (conreu convencional, CT, conreu reduït, RT, No conreu, NT) i tres dosis de fertilització mineral N (0, 200, 400 kg N ha-1) en un disseny de blocs a l'atzar amb tres repeticions. El 2015, es va crear un experiment adjacent (experiment a curt termini, STE) amb el mateix disseny que el LTE però amb una gestió anterior diferent basada en NT. En el LTE, les emissions de CO2, CH4 i N2O del sòl es van quantificar durant tres anys. A més, es va calcular el factor d'emissió de N2O (EF) i les emissions de N2O a escala de rendiment. També, es va calcular la taxa anual del segrest de SOC (ΔSOCrate) (0-40 cm de profunditat) per a cada tractament en tres períodes diferents (P1-, P2-, P3-) en condicions de secà (-R) i condicions de regadiu (-I) (P1-R, de 1996 a 2009; P2-R, de 2009 al 2015; P3-I, de 2015 a 2017). A més, en LTE i STE superfície del sòl (0-5 cm) es van mesurar macroagregats secs i estables en l’aigua i la seva concentració de C, així com altres fraccions del sòl (concentració total de SOC i concentració de C làbil). Així mateix, es va analitzar la resistència a la penetració en la superfície del sòl (PR) i la infiltració d'aigua durant la segona temporada de cultiu de blat de moro (és a dir, l'any 2016). Ingualment, en els dos camps experimentals, es va mesurar anualment la biomassa aèria, el rendiment de gra, els components de rendiment i l'eficiència d'ús d'aigua i nitrogen (WUE i NUE, respectivament). En els agroecosistemes Mediterranis recentment transformats a regadiu, una reducció de la dosi de fertilització N juntament amb una reducció en el conreu, és una estratègia òptima en termes de manteniment de la productivitat dels cultius. A més, la reducció del conreu millora l'estat estructural del sòl, per tal de proporcionar al sòl suficient resistència i assegurar un desenvolupament òptim dels cultius. Si bé la reducció del conreu genera més emissions de GEH del sòl a l'atmosfera, aquestes es compensen amb un major rendiment de blat de moro i segrest de SOC.Las áreas de secano Mediterráneas se transforman en regadio para estabilizar o aumentar el rendimiento de los cultivos. La ocupación gradual del riego lleva a un aumento en el uso de nitrógeno y la intensidad del laboreo. Por lo tanto, el objetivo principal de este estudio fue la evaluar los efectos de los diferentes sistemas de laboreo y las dosis de fertilizantes de N en las emisiones de GEI (metano, CH4; dióxido de carbono, CO2, óxido nitroso, N2O) a la atmósfera, así como, el secuestro de C del suelo, la estructura de la superficie del suelo y la productividad del cultivo en un área recientemente transformada a regadío. Para lograr ese objetivo, se llevó a cabo un estudio en NE España en un experimento de larga duración (LTE) de laboreo y dosis de fertilización N establecido en 1996 bajo la producción de cebada (Hordeum vulgare L.) en secano, posteriormente, se transformó en monocultivo maíz (Zea mays L.) con riego por aspersión en 2015. Este estudio se realizó durante tres campañas consecutivas de cultivo de maíz (es decir, los años 2015, 2016 y 2017). Se compararon tres tipos de laboreo (laboreo convencional, CT, laboreo reducido, RT, No laboreo, NT) y tres dosis de fertilización mineral N (0, 200, 400 kg N ha-1) en un diseño de bloques al azar con tres repeticiones. En 2015, se creó un experimento adyacente (experimento a corto plazo, STE) con el mismo diseño que el LTE pero con una gestión anterior diferente basada en NT. En el LTE, las emisiones de CO2, CH4 y N2O del suelo se cuantificaron durante tres años. Además, se calculó el factor de emisión de N2O (EF) y las emisiones de N2O a escala de rendimiento. También, se calculó la tasa anual de secuestro de SOC (∆SOCrate) (0-40 cm de profundidad) para cada tratamiento en tres periodos diferentes (P1-, P2-, P3-) en condiciones de secano (-R) y condiciones de regadio (-I) (P1-R, de 1996 a 2009; P2-R, de 2009 a 2015; P3-I, de 2015 a 2017). Además, en LTE y STE superficie del suelo (0-5 cm) se midieron macroagregados secos y estables en agua y su concentración de C, así como otras fracciones del suelo (concentración total de SOC y concentración de C lábil). Asimismo, se analizaron la resistencia a la penetración en la superficie del suelo (PR) y la infiltración de agua durante la segunda temporada de cultivo de maíz (es decir, el año 2016). Ingualmente, en ambos campos experimentales, se midió anualmente la biomasa aerea, el rendimiento de grano, los componentes de rendimiento y la eficiencia de uso de agua y nitrógeno (WUE y NUE, respectivamente). En los agroecosistemas Mediterráneos recientemente transformados a regadio, una reducción de la dosis de fertilización N junto con una reducción en el laboreo, es una estrategia óptima en términos de mantenimiento de la productividad de los cultivos. Además, la disminución del laboreo mejora el estado estructural del suelo, a fin de proporcionar al suelo suficiente resistencia y asegurar un desarrollo óptimo de los cultivos. Si bien la reducción del laboreo genera mayores emisiones de GEI del suelo a la atmósfera, estas se compensan con un mayor rendimiento de maíz y secuestro de SOC.Mediterranean rainfed areas are transformed into irrigation to stabilize or increase crop yields. The gradual occupation of irrigation leads to an increase in nitrogen use and intensity of tillage. Therefore, the main objective of this study was the identification of the effect of different tillage systems and N fertilizer rates on GHG emissions (methane, CH4; carbon dioxide, CO2; nitrous oxide, N2O) to the atmosphere, as well as, soil C sequestration, soil surface structure and crop productivity when converting rainfed lands to irrigated. In order to achieve that objective a study was carried out in NE Spain in a long-term (LTE) tillage and N rate field experiment established in 1996 under rainfed barley (Hordeum vulgare L.) conditions which was converted to irrigation with maize (Zea mays L.) monoculture as cropping system in 2015. This study was conducted during three consecutive maize growing seasons (i.e. years 2015, 2016, and 2017). Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha-1) were compared in a randomized block design with three replications. In 2015, an adjacent experiment (short-term experiment, STE) with the same layout as the LTE but with different previous management based on NT was set up. In the LTE, soil CO2, CH4 and N2O emissions were quantified during three years. Also, N2O emission factor (EF) and yield-scaled N2O emissions were determined. In addition, annual SOC sequestration rate (∆SOCrate) (0-40 cm depth) was calculated for each treatment in three different periods (P1-, P2-, P3-) under rainfed (-R) conditions and irrigated (-I) conditions (P1-R, from 1996 to 2009; P2-R, 2009 to 2015; P3-I, from 2015 to 2017). Moreover, in LTE and STE soil surface (0-5 cm) dry and water-stable macroaggregates and their C concentration, as well as other soil fractions (total SOC concentration and labile C concentration) were measured. Also soil surface penetration resistance (PR), and water infiltration were analyzed during the second maize growing season (i.e. year 2016). In addition, in both experimental fields, above ground biomass, maize grain yield, yield components and water and nitrogen use efficiency (WUE and NUE, respectively) were measured annually. In Mediterranean agroecosystems recently transformed to irrigated land, a reduction in N fertilization rate together with a reduction in tillage are optimum strategies in terms of maintenance of crop productivity. In addition, reductions of tillage improve the structural state of the soil, in order to provide the soil enough resilience and ensure an optimum development of crops. Although the reduction of tillage generates higher GHG emissions from the soil to the atmosphere, this is compensated by a greater maize yield and SOC sequestration

Physiological Activity of <i>Quercus suber</i> with a High Presence of <i>Cerambyx welensii</i>

The wood borer Cerambyx welensii Küster is a key contributor to Quercus open woodland (dehesa) decline. Among other factors, olfactory and visual cues could influence host colonisation by this species. In this study, we investigated whether the physiological performance and morphological features of Q. suber trees under summer stress are affected by C. welensii infestation. Additionally, we analysed the relation between morpho-physiological variables and the emission of monoterpenes that potentially mediate host selection by C. welensii. Thirty-six Q. suber trees with known monoterpene emission profiles were selected: 18 trees highly visited by C. welensii, and 18 neighbouring trees not visited or at least not visibly damaged by this wood borer. For each tree, we assessed photosynthesis, stomatal conductance, and transpiration during the early evening, and also the perimeter and crown projection. Trees visited by C. welensii maintained higher photosynthetic activity than non-visited trees (1.5–2.15 times) from 19:35 to 20:45 h. Visited trees had larger perimeters and smaller crown projection area-to-perimeter ratios than non-visited trees. Results suggest that, under stress conditions, the physiological performance of trees infested by C. welensii could have favoured foliar emission of certain monoterpenes influencing intraspecific host selection by this species

Soil organic carbon sequestration when converting a rainfed cropping system to irrigated corn under different tillage systems and N fertilizer rates

42 Pags.- 5 Tabls.- 4 Figs. © 2020 The Authors. Soil Science Society of America Journal © 2020 Soil Science Society of AmericaThe aim of this study was to evaluate the impact of 21 years of tillage and N fertilization and the conversion from a rainfed to an irrigated cropping system on soil organic C (SOC). The study was carried out in northeastern Spain in a long‐term tillage and N rate field experiment established in 1996 under barley rainfed conditions, which in 2015 was converted into irrigation with corn. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no‐tillage, NT) and three mineral N fertilization rates (0, 60, and 120 kg N ha−1 under barley, and 0, 200, and 400 kg N ha−1 under corn) were compared. Annual C‐inputs as aboveground crop residues and annual SOC sequestration rate (∆SOCrate) (0–40 cm depth) were calculated in three different periods (P1, P2 and P3) under rainfed (‐R) and irrigated (‐I) conditions (P1‐R, from 1996 to 2009; P2‐R, from 2009 to 2015; P3‐I, from 2015 to 2017). At the end of P3‐I, particulate organic C (POC) was measured from the 0–5, 5–10, 10–20, 20–30, and 30–40 cm depths. Averaged over all treatments, ∆SOCrate was 492, 222, and 969 kg C ha−1 yr−1 for P1‐R, P2‐R, and P3‐I, respectively. In P1‐R and P3‐I, C‐input explained 70% of the variability of ∆SOCrate. In P1‐R, ∆SOCrate followed the order NT > RT > CT, while for N rate, order was high > medium > 0. In P3‐I at the highest N rate, ∆SOCrate followed the order NT > RT > CT. In P2‐R, ∆SOCrate did not show differences between tillage and/or N rate treatments. The increase in SOC after conversion from a rainfed to an irrigation system was mainly explained by POC, which was increased by 75% compared to the previous rainfed period. The modification of the cropping system through the introduction of irrigation and adequate crop management practices under no‐tillage and adjusted N fertilizer rates can contribute to the sequestration of large amounts of atmospheric CO2.This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784) and is Ramón y Cajal fellow (RYC2018-024536-I) of the Ministerio de Ciencia, Innovacion y Universidades.Peer reviewe