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Management practices in the inter-row area of olive orchards are undergoing significant transformations. Current regulations and recommendations are increasingly advocating the implementation of temporary spontaneous cover crops (TSCV) mainly to reduce erosion. Existing research has predominantly focused on evaluating the effectiveness of TSCV in mitigating soil erosion in olive orchards, with limited attention given to carbon (C) cycling, despite the potential of TSCV for contributing to the removal of atmospheric CO 2 and in the reduction of eroded carbon. Moreover, the limited number of studies on the effects of TSCV on C cycling have been confined to a few experimental sites and at the short term. This study aimed to assess the potential of TSCV to enhance carbon sequestration and nitrogen retention in rainfed commercial olive orchards under semi-arid conditions. To achieve this, we evaluated the annual aboveground organic carbon input due to TSCV, as well as the stocks of soil organic (SOC) and inorganic (SIC) carbon and total N (STN) in 24 commercial olive groves with calcareous Regosols and calcium Cambisols as the predominant soil types that have implemented TSCV for at least the last 8 years. These were compared with 24 comparable groves with bare soil (BS). Net aboveground annual carbon and CO 2 fixation of the TSCV averaged 125.7 kg C ha−1 y−1 and 460 kg CO 2 ha−1 y−1, respectively, which are figures relatively low mainly due to the low area covered by the TSCV. After eight years of implementing TSCV, the SOC stocks increased by an average of 2.03 Mg C ha−1 (in the top 30 cm of soil) compared to BS olive orchards. Moreover, SOC content of unprotected (>250 µm) and physically protected (53–250 µm) fractions were 82 and 38 % higher in the TSCV olive farms. Although there was a tendency of lower SIC content in TSCV olive orchards, differences were not significant. The STN content and the potentially mineralizable nitrogen in TSCV farms were on average 26 % and 77 % higher than in BS olive orchards. These findings underscore the potential of TSCV for organic carbon accumulation and nitrogen retention in the soil, contributing to climate change mitigation and soil fertility enhancement. Increasing vegetation coverage and productivity can enhance their effectiveness. • With TSCV on Calcareous Regosols and calcium Cambisols, SOC and STN were 25–26 % higher. • After 8 years of implementing TSCV, there were 2.0 Mg ha−1 (0–30 cm depth) more SOC compared to BS olive orchards. • Unprotected and physically protected C were the SOC fractions which most increased under TSCV. • SIC content tended to be lower under TSCV. • TSCV in olive groves demonstrated to contribute to climate change mitigation and N retention. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

• No-tillage significantly increased soil CO 2 emissions at the highest N-fertilizer rate. • Soil CO 2 emission depends on soil temperature and moisture. • Soil acted as a CH 4 sink in all treatments. • Reduced and no-tillage increased above-ground C-inputs at the highest N-fertilizer rate. In newly irrigated Mediterranean agroecosystems, the combined effect of tillage and N fertilization on soil carbon dioxide (CO 2) and methane (CH 4) fluxes is at present poorly understood. The goal of this study was to quantify both soil CO 2 and CH 4 emissions as well as crop performance under different tillage systems and N fertilization rates during three maize (Zea mays L.) growing seasons (2015–2017) in a semiarid area converted to irrigated. Three types of tillage (conventional tillage, CT, reduced tillage, RT, and no-tillage, NT) and three mineral N fertilization rates (0, 200, and 400 kg N ha−1) were compared in a randomized block design with three replications. Weekly soil CO 2 and CH 4 emissions, soil temperature and gravimetric moisture were measured. Moreover, maize above-ground biomass, grain yield, and above-ground C-inputs were quantified. Carbon dioxide emissions ranged from 173 to 4378 mg CO 2 -C m-2 d-1. No-tillage showed a greater mean soil CO 2 flux than CT when applying the highest rate of N (400 kg N ha-1). Although some emissions of CH 4 were observed, all treatments acted as net CH 4 sinks during most of the experimental period. A linear multiple relationship between soil CO 2 fluxes and soil gravimetric moisture (0–5 cm depth) and temperature (10 cm depth) were found. In the 2015 growing season, greater cumulative CO 2 emissions were found under NT and RT compared with CT, while in 2016 N T showed the highest values compared to CT with intermediate values in RT. Differently, in 2017 no differences between tillage systems were found. When applying N fertilizer, NT and RT increased maize grain production and above-ground C-inputs compared to CT, since a severe soil crusting occurred in this last, which caused crop water deficit. The results suggest that tillage intensity and N fertilization rate reduction can increase maize biomass production and yield which leads to greater C-input that returns to the soil. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the most appropriate soil management to reduce the structural degradation of soils susceptible to crusting in Mediterranean areas recently transformed into irrigation. A long-term field experiment (LTE) under rainfed conditions was established in 1996 in NE Spain to compare three tillage systems (no-tillage, NT; reduced tillage, RT; conventional tillage, CT). The experiment was transformed to irrigated corn in 2015. In 2015, an adjacent experiment with the same layout was created (short-term experiment, STE) in an area previously managed under long-term NT. The study was carried out during the second corn growing season (i.e. year 2016). Soil samples were collected from 0 to 5 cm depth at different dates during corn season. Dry and water-stable macroaggregates and their C concentration, soil organic carbon (SOC) and labile C concentration, soil respiration, bulk density, penetration resistance (PR), water infiltration, macroporosity, microporosity, amount of crop residues and ground cover, corn development, aerial biomass, and grain yield were measured. In LTE and STE tillage led to a breakdown of dry sieved aggregates (of 2–4 and 4–8 mm size) in RT and CT, being slowly reconsolidated throughout the corn growing season. However, macroaggregate water-stability did not increase in CT and RT compared to NT due to a lower SOC concentration, making the soil more susceptible to its degradation by the action of water. SOC differences between treatments were more pronounced in LTE than STE given the long-term differential management in the first, which allowed greater accumulation of SOC under NT. In LTE, PR between corn rows was greater under NT than CT and RT and non-significantly different between treatments within the row. In the case of STE, PR increased over time after tillage (CT and RT) to match NT in the last sampling. Crop establishment was slower in CT than NT in LTE highlighting the impact of soil surface degradation on crop development. However, contrarily to the differences in corn yield in 2015, a careful planting in 2016 led to a lack of differences between tillage systems on corn yield. Our results indicate that in areas transformed into irrigation intensive tillage leads to greater susceptibility to soil structural degradation. Thus, in these areas the adoption of conservation agriculture practices such RT and NT enhances soil resilience to degradation processes and ensures an adequate development of the crop. [ABSTRACT FROM AUTHOR]

• An increase in the fertilizer N rate increased N 2 O emissions in irrigated corn. • No-tillage significantly increased soil N 2 O emission at the highest N-fertilizer rate. • Denitrification was the main pathway under no-tillage for N 2 O emission. • The use 200 kg N ha−1 reduced the yield-scaled N 2 O emissions in the first out of three years. • The emission factor was much lower than 1% proposed by IPCC. 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 (N 2 O) 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 N 2 O emissions and their relationship with maize grain yield to determine the best management system to reduce yield-scaled N 2 O 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 N 2 O emissions, water-filled pore space, soil temperature, mineral N content (as NH 4 + and NO 3 −), 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 N 2 O emissions. Furthermore, the lowest N 2 O fluxes were observed in CT when WFPS was below 40% and the highest N 2 O fluxes were seen in NT when WFPS was above 60% coinciding with the greatest denitrification potential. Cumulative N 2 O 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 N 2 O emission compared to the control. Only RT showed differences between growing seasons on cumulative N 2 O emissions, with greater values in 2017 compared to 2015, and intermediate values in 2016. In all treatments, the N 2 O 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 N 2 O emissions than CT in Mediterranean agroecosystems recently converted to irrigation. [ABSTRACT FROM AUTHOR]

There is a strong need to identify agricultural management practices that maintain agronomic productivity while diminishing soil N 2 O emissions. The yield-scaled N 2 O emissions (YSNE) indicator can help to evaluate the adequacy of a given agricultural practice under both aspects. Long-term (18-yr) soil water and mineral N dynamics, crop biomass and yields, and 2011–2012 soil N 2 O emissions and ancillary variables were measured on barley ( Hordeum vulgare L.) production in a tillage (conventional tillage, CT; no-tillage, NT) and N rate (0, 60 and 120 kg N ha −1 ) combination under rainfed Mediterranean conditions (NE Spain). Once evaluated, the STICS soil-crop model was used to simulate the 18-yr soil N 2 O emissions of each tillage system under increasing N rates (0, 30, 60, 90 and 120 kg N ha −1 ) in order to identify optimum management to reduce YSNE, being initialized with observed data. Cropping season precipitation was highly variable during the experiment, being a key regulating mechanism for crop yields and simulated soil N 2 O emissions. Crop yield under NT with N outperformed CT in 11 years. STICS performed reasonably well when simulating cumulative N 2 O emissions and ancillary variables with model efficiencies greater than 0.5. The 18-yr average simulated cumulative N 2 O emissions were 0.50, 0.82 and 1.09 kg N 2 O-N ha −1  yr −1 for CT-0, CT-60 and CT-120, respectively, and they were 0.53, 0.92 and 1.19 kg N 2 O-N ha −1  yr −1 for their counterparts under NT. These averages mask a large variability between years, according to precipitation. The 18-yr mean yield-scaled N 2 O emissions were 2.8–3.3 times lower under NT, compared to the corresponding CT treatments. Under CT, N application would increase YSNE in most years while YSNE would be more resilient to the application of increasing N rates under NT. Our work demonstrates that in rainfed Mediterranean systems NT is a win-win strategy for the equilibrium between agricultural productivity and low soil N 2 O emissions. [ABSTRACT FROM AUTHOR]