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Conservation tillage is recognized as a sustainable management practice, however its combination with organic residues application still constitutes a challenge in some areas. A field trial was established in a semiarid agro-ecosystem to study the effects of different crop nutrient sources under minimum tillage (MT). Application of organic amendments at the beginning of a five-year crop rotation (ORG treatment) was evaluated and compared to the control plot where wheat was continuously grown with traditional mineral fertilization (MIN treatment). In addition to wheat yield and biomass, several soil properties were measured (pH, soil nutrients (i.e., Olsen P, exchangeable K, and mineral N), soil organic matter (i.e., C, N, C/N ratio), potentially mineralizable nitrogen, total microbial activity and heavy metals) throughout the 10-year study. The wheat yield was significantly higher under the ORG treatment than under the MIN, although climatic conditions (e.g., rainfall) exerted a great influence too. The organic amendments increased soil nutrients content mainly right after their application but the levels were adequate for the whole crop rotation. Plots under organic amendment application did not accumulate significantly more soil organic matter than those mineral-fertilized, probably due to the low protective capacity of coarse-textured soils. The application of organic amendments under MT resulted in a promising management agro-ecosystem compared to the mineral fertilized because crop nutrients came from organic wastes, no herbicides were applied while the yields were higher., This work was funded by INIA (AT2017-003), the Ministry of Science and Innovation (RTA2017-00006-C03-01, AGL2017-83283-C2-1/2-R), the EJPSoil [CarboSeq] project (which has re ceived funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 862695), the Community of Madrid (AGRISOST-CM S2018/BAA-4330) and European Structural funding 2014-2020 (ERDF y ESF)

13 Pág. Departamento de Medio Ambiente y Agronomía​, Soil aggregates can be considered massive microbial incubators. Thus, the study of the bacteria and fungi colonizing different soil aggregate fractions helps to elucidate the factors influencing the associations between microhabitats in soil aggregates and microbial functioning. The main objective of this study was to evaluate the total bacterial and total fungal abundances and soil quality-related parameters of four aggregate size fractions (>2 mm, 2–0.25 mm, 0.25–0.053 mm and 2 mm), which constituted only 16.7% (with 0.17 OC/100 g soil) under this treatment at 0–5-cm depth, compared with 50.7% (with 1.34 g OC/100 g soil) in uncultivated soil. The abundances of bacteria and fungi exhibited contrasting responses to soil management across aggregate fractions, which differed by depth. The abundance of bacteria, but not fungi, was closely related to OC and N concentrations, with higher values in macroaggregates than in microaggregates for TT and DS at 0–5 cm depth. Uncultivated soil showed no OC differences across aggregate fractions and the bacteria were distributed uniformly among them. Fungal abundance was higher in microaggregates, mainly in DS, concurrent with lower bacterial abundance. Therefore, bacteria and fungi responded differently to changes in properties at the aggregate scale induced by soil management within the soil surface horizon. Highlights: Management practices affect aggregate size distribution and their bacterial and fungal abundances Tillage reduced the OC stored in macroaggregates >2 mm by 87% compared to uncultivated soil Bacterial abundance was positively correlated with the C and N concentrations inside aggregates Fungal abundance showed an important negative correlation with the bacterial abundance., Comunidad de Madrid, Grant/Award Number: AGRISOST S2018/BAA-4330; Ministerio de Ciencia e Innovación, Grant/Award Number: GL2017-83283-C2-1-R; Community of Madrid; Spanish Ministry of Science and Innovation

Nitrogen (N) losses from agricultural systems increase air and water pollution, and these losses are highly correlated with the excessive fertilization. An adjusted N fertilization is then a key factor in increasing the N fertilizer efficiency, and leaf clip sensors can help to improve it. This study (combining five different field experiments in Central Spain) tried to identify the ability of the clip sensors in maize N status identification and yield prediction, comparing two different devices (SPAD-502&reg, and Dualex&reg, ) and identifying the best protocol for maize leaf sampling. As a result, the study demonstrated that different leaf clip chlorophyll sensors presented similar results, although some differences appeared at larger N concentrations. Complementary polyphenol information (as flavonol) can improve the maize N deficiency prediction. Moreover, valuable information for a proper sampling protocol was obtained with this study. It proved that the sampling position (in the leaf and in the plant) and sampling time were crucial for a better estimation of the maize N status. Proper fertilization recommendations could be achieved based on clip chlorophyll sensor measurements.

8 Pág. Departamento de Medio Ambiente y Agronomía​, Replacement of bare fallow in rotations by cover crops is a promising tool to reduce crusting, although the interactions with the soil moisture and the effect of the cover crop species are still not well understood. The objective of this work was to determine how cover crops modify the soil surface response to penetration and their relation with the soil water content. Two winter cover crops, barley (Hordeum vulgare L.) and vetch (Vicia sp. L.), were compared with a bare fallow treatment in a 10-year field experiment in central Spain. Soil resistance to penetration and soil water content were intensively measured (76 sampling dates) at two surface depths, using two types of surface penetrometers. Under the barley cover crop, the number of very dry events was reduced by around 20%, compared to the bare fallow. The soil resistance to penetration was closely related to the surface soil water content (R2 = 0.65) and cover crops affected it through soil moisture modification. In this line, the greater mulch provided by barley cover crop respect to vetch, increased the soil water content prior to main crop seeding, resulting in less resistance to penetration during this critical period. The good performance of barley resulted in a reduction of more than 60% of the soil resistance to penetration between the 3rd and 8th year of the experiment (7.2–2.9 kg cm−2, respectively). Even under bare fallow, soil strength was decreased after ten years with reduced tillage. Therefore, the maintenance of cover crop residues over surface soil together with reduced tillage enhanced the soil surface conditions and steadily reduced the risk of crust formation. Expected enhancement of main-crop germination, water infiltration, soil aeration and erosion mitigation may be attained by cover-cropping in degraded soils., This work was supported by the Comisión Interministerial de Ciencia y Tecnología (AGL2014-52310-R, AGL2017-83283-C2-1-R and 2-R); and Comunidad de Madrid (AGRISOST-CM S2018/BAA-4330 project) and Structural Funds 2014-2020 (ERDF and ESF). We would like to thank the staff from La Chimenea field station (Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario) for their helpful assistance.

8 Pags.- 5 Tabls.- 3 Figs., For quite a long time, soil organic carbon stock (SOCS) has reduced from reconverting forest areas into agricultural land or by inadequate agronomic practices. However in recent decades in Mediterranean areas, abandonment of agricultural areas due to lack of economic profits and to promoting tourism has fostered a change in land use that has impacted soil carbon. In line with this, the Majorca Island (Spain) could be a good study area to evaluate temporary changes in carbon stocks in soils in areas with a Mediterranean climate. The present study analysed the spatial distribution of SOCS and evaluated the temporal changes over 11 years in agricultural soils in relation to the influence of land use and land management’. The global carbon budget (estimated at 30 cm depth) on the Majorca Island was estimated at 31.23 Tg C, and showed wide spatial variability. As expected, SOCS was higher in the forest areas of the Tramuntana Mountain Range (>100 Mg ha−1), while the lowest contents were found in agricultural use (79.3 Mg ha−1), located mainly in the centre and south of this island. The total C stored from 2006 to 2017 increased by 2.62 Tg C (15%) in agricultural areas on the island. We noted a major increase in SOCS in the agricultural zones on mountain slopes (>2-fold higher), associated with abandoned crops in terrace cultivation, but grassland systems also increased. Nonetheless, the present study shows a sharp drop in SOCS in the centre and south of this island. This decrease was more pronounced in annual crops (−14.5%), which could be attributed to intensive soil management and increased irrigated land. Land abandonment has been indicated as the main potential to carbon sequestration in soil, but this potential for carbon sequestration is a finite process. Certain changes in agricultural practices on Majorca, and in rural Mediterranean areas in general, are necessary to avoid carbon loss in cropland soils. Adoption of conservation agriculture practices, e.g. cover crops, crop rotation, organic additions and reduced tillage techniques, can help increase SOC levels in rural Mediterranean areas., We greatly appreciate the financial assistance provided by Spanish Ministry (Project CGL2013-43675-P).

Cover cropping in agriculture is expected to enhance many agricultural and ecosystems functions and services. Yet, few studies are available allowing to evaluate the impact of cover cropping on the long term change of soil hydrologic functions. We assessed the long term change of the soil hydraulic properties due to cover cropping by means of a 10-year field experiment. We monitored continuously soil water content in non cover cropped and cover cropped fields by means of capacitance probes. We subsequently determined the hydraulic properties by inverting the soil hydrological model WAVE, using the time series of the 10 year monitoring data in the object function. We observed two main impacts, each having their own time dynamics. First, we observed an initial compaction as a result of the minimum tillage. This initial negative effect was followed by a more positive cover crop effect. The positive cover crop effect consisted in an increase of the soil micro- and macro-porosity, improving the structure. This resulted in a larger soil water retention capacity. This latter improvement was mainly observed below 20 cm, and mostly in the soil layer between 40 and 80 cm depth. This study shows that the expected cover crop competition for water with the main crop can be compensated by an improvement of the water retention in the intermediate layers of the soil profile. This may enhance the hydrologic functions of agricultural soils in arid and semiarid regions which often are constrained by water stress.

Conservation tillage and crop rotations improve soil quality. However, the impact of these practices on greenhouse gas (GHG) emissions and crop yields is not well defined, particularly in dry climates. A rainfed 2-year field-experiment was conducted to evaluate the effect of three long-term (17–18 years) tillage systems (Conventional Tillage (CT), Minimum Tillage (MT) and No Tillage (NT)) and two cropping systems (rotational wheat ( Triticum aestivum L.) preceded by fallow, and wheat in monoculture), on nitrous oxide (N 2 O) and methane (CH 4 ) emissions, during two field campaigns. Soil mineral N, water-filled pore space, dissolved organic carbon (C) and grain yield were measured and yield-scaled N 2 O emissions, N surplus and Global Warming Potentials (GWP) were calculated. No tillage only decreased cumulative N 2 O losses (compared to MT/CT) during campaign 1 (the driest campaign with least fertilizer N input), while tillage did not affect CH 4 oxidation. The GWP demonstrated that the enhancement of C stocks under NT caused this tillage management to decrease overall CO 2 equivalent emissions. Monoculture increased N 2 O fluxes during campaign 2 (normal year and conventional N input) and decreased CH 4 uptake, as opposed to rotational wheat. Conversely, wheat in monoculture tended to increase soil organic C stocks and therefore resulted in a lower GWP, but differences were not statistically significant. Grain yields were strongly influenced by climatic variability. The NT and CT treatments yielded most during the dry and the normal campaign, and the yield-scaled N 2 O emissions followed the same tendency. Minimum tillage was not an adequate tillage management considering the GWP and the yield-scaled N 2 O emissions (which were 39% lower in NT with respect to MT). Regarding the crop effect, wheat in rotation resulted in a 32% increase in grain yield and 31% mitigation of yield-scaled N 2 O emissions. Low cumulative N 2 O fluxes ( 2 O-N ha −1 campaign −1 ) highlighted the relevance of soil organic C and CO 2 emissions from inputs and operations in rainfed semi-arid cropping systems. This study suggests that NT and crop rotation can be recommended as good agricultural practices in order to establish an optimal balance between GHGs fluxes, GWP, yield-scaled N 2 O emissions and N surpluses.

Crop rotation with legumes and conservation tillage systems are advisable practices in rainfed Mediterranean agro-ecosystems, since, in these areas, soils are broadly characterized by low organic matter contents and low fertility. These management practices can substantially modify the dynamics of soil greenhouse gas (GHG) emissions, carbon sequestration and carbon dioxide (CO 2 ) emissions derived from system inputs and farm operations. In this context, a field experiment was conducted under Mediterranean conditions to evaluate the effect of three long-term tillage systems (no tillage (NT), minimum tillage (MT) and conventional tillage (CT)) and two crops (vetch (V, Vicia sativa L.) versus barley (B, Hordeum vulgare L.)) on nitrous oxide (N 2 O), methane (CH 4 ) and CO 2 emissions during one year. Crop yields, soil mineral nitrogen concentrations, dissolved organic carbon and GHG fluxes were measured during the growing season. Soil organic carbon was measured in spring 2012 (18 years after the beginning of a long-term tillage experiment) and together with input and fuel consumption by farm machinery was used to compare the Global Warming Potential (GWP) of the different crop and tillage treatments. Cumulative fluxes of N 2 O ranged between 0.16 (B-MT) and 0.29 (V-MT) kg N 2 O-N ha −1 yr −1 , resulting in a lower impact on Net GWP than in previous studies. A significant ‘tillage × crop’ interaction was observed in cumulative N 2 O emissions (V resulted in higher N 2 O losses than barley in CT and MT, whereas similar fluxes were observed under NT), which was influenced by soil water-filled pore space, dissolved organic carbon content and denitrification losses, in spite of the presumable predominance of nitrification. Neither tillage nor crop influenced CH 4 or CO 2 emissions. Yield-scaled N 2 O emissions (YSNE) were low ( 2 O-N kg aboveground N uptake −1 ) and significantly higher in B than in V. The most sustainable crop and tillage treatments in terms of GWP were non-fertilized-V and NT, due to higher carbon sequestration and lower fuel consumption under NT and the absence of mineral N fertilizers in V. These crop and tillage treatments could be considered good management strategies in rainfed Mediterranean agro-ecosystems since they provide the best balance between soil emissions, YSNE and Net GWP.

The agronomic practices used to manage the soil play an important role in the maintenance of biological diversity within crop fields. Conservation agriculture technology has been extensively adopted in dry land conditions. In these systems, the relationship between soil properties and weed density and soil weed seed bank has not been explored deeply. We conducted this study in order to (1) examine the cumulative impact of tillage systems (CT, MT and NT) on weed emergence on the field; (2) test the effects of different tillage and crop systems on weed species density and diversity (Shannon's index, Pielou index and species richness) within the transient and persistent seed bank of the soil; and (3) analyse the impact of two soil parameters on weeds water stable aggregates (WSA) and particulate organic matter content (C-POM). The highest weed density was recorded in conservation tillage systems (MT and/or NT) several years after the implementation of these systems. Additionally, the cumulative effects of conservation tillage techniques were found to have increased the seed density and species diversity in soil seed bank, which was probably due to particular conditions created in the soil; a low or negligible level of soil disturbance (as is expected with MT and NT) possibly allowed seeds to keep in the soil seed bank and remain dormant, due to, among other reasons, improved water stable aggregates and organic matter content. Results from the study confirm the complexity of the matrix formed by weed-seed bank-soil. © 2016 Elsevier B.V.

Conservation agriculture (CA) practices have been widely applied on a variety of agro-ecosystems in order to prevent soil degradation and to improve fertility. We studied the long term influence of different management systems on soil properties in an experimental field located in semiarid central Spain. Soil organic carbon (SOC), dissolved organic carbon (DOC), soil basal respiration (CO2-C), microbial biomass carbon (MBC) and β-glucosidase activity have been measured during three cropping seasons. Results showed a high influence of date of sampling on the evaluated parameters and on the microbial status and activity, most likely due to variations in soil water content (SWC). Microbial efficiency and β-glucosidase activity were improved under CA, as SOC, DOC and MBC were accumulated in the surface. Microbial efficiency ratios, e.g.;qR (qR=MBC/SOC), qCO2 (qCO2=CO2-C /MBC) and qCO2/SOC, were useful to explain the influence of sampling date and the management practices on the microbial status. A stepwise procedure reduced considerably our data set, allowing the selection of MBC, DOC and qCO2/SOC as reliable indicators to evaluate soil quality in semiarid areas. © 2015 Elsevier B.V.

The arable fields in central Spain have been dominated by cereal production, especially winter wheat. In this area, the defined action of weed management program requires a clear understanding of the factors and mechanisms conditioning weed community dynamics in agro systems. This study evaluated the effects of different agricultural management systems on the abundance and diversity of weed communities in winter wheat crops.Weed density and composition of weed species were sampled over four years; comparing monoculture wheat and rotational wheat in three agricultural management systems (1) direct drilling (no-tillage, NT); (2) chisel ploughing (minimum tillage 15. cm depth, MT) and (3) mouldboard ploughing (traditional tillage 20. cm depth, CT). With the aim to be able to improve weed management in agro systems with semiarid environments; within each of the agricultural management systems, we examined the impact of mineral fertilization (traditional and balanced) as a tool for reducing the external inputs in arable cereals.Weed diversity was assessed using the three common diversity indices Shannon's index, evenness index and species richness. The data collected showed total weed density was different per tillage system and each year of the study, but we did not find significant differences between crop systems over the study.The abundance, diversity and evenness of the weed community in the arable field, were significantly increased in NT systems. Within the direct drilling (NT) plots, rotational wheat showed the highest levels of weed infestation and diversity. Comparing traditional and balanced mineral fertilization of soil did not reveal a significant effect on weed abundance and diversity observed in field. © 2013 Elsevier B.V.

In semiarid areas, traditional, intensive tillage has led to the depletion of soil organic matter, which has resulted in reduced soil fertility. The aim of the present work was to evaluate the effects of different soil management systems, practised over 12 years, on soil organic carbon (SOC), nitrogen (SN) and biologically active organic matter (particulate organic matter [POM]; potentially mineralisable nitrogen [PMN]; microbial biomass [MB]). A Mediterranean Alfisol, located in central Spain, was managed using combinations of conventional tillage (CT), minimum tillage (MT) or no-tillage (NT), plus a cropping background of either continuous wheat (WW) or a fallow/wheat/pea/barley rotation (FW). Soil was sampled at two depths on four occasions during 2006-2007. The results showed the sampling date and the cropping background to significantly affect the SOC (p

Crop simulation models allow analyzing various tillage-rotation combinations and exploring management scenarios. This study was conducted to test the DSSAT (Decision Support System for Agrotechnology Transfer) modelling system in rainfed semiarid central Spain. The focus is on the combined effect of tillage system and winter cereal-based rotations (cereal/legume/fallow) on the crop yield and soil quality. The observed data come from a 16-year field experiment. The CERES and CROPGRO models, included in DSSAT v4.5, were used to simulate crop growth and yield, and DSSAT- CENTURY was used in the soil organic carbon (SOC) and soil nitrogen (SN) simulations. Genetic coefficients were calibrated using part of the observed data. Field observations showed that barley grain yield was lower for continuous cereal (BB) than for vetch (VB) and fallow (FB) rotations for both tillage systems. The CERES-Barley model also reflected this trend. The model predicted higher yield in the conventional tillage (CT) than in the no tillage (NT) probably due to the higher nitrogen availability in the CT, shown in the simulations. The SOC and SN in the top layer only, were higher in NT than in CT, and decreased with depth in both simulated and observed values. These results suggest that CT-VB and CT-FB were the best combinations for the dry land conditions studied. However, CT presented lower SN and SOC content than NT. This study shows how models can be a useful tool for assessing and predicting crop growth and yield, under different management systems and under specific edapho-climatic conditions. Additional key words: CENTURY model; CERES-Barley; crop simulation models; DSSAT; sequential simula- tion; soil organic carbon.

One practice for reclaiming degraded agricultural soils under semiarid climate is to use organic amendment to improve the physical, chemical, and biological properties of the soil, therefore enhancing its fertility. A short-term field experiment was carried out to study the effects of different biosolid rates on selected soil properties and assess these as potential indicators of soil restoration. The organic waste was surface-applied once at three rates (30, 60, and 90 Mg ha-1) to an abandoned agricultural soil. Three years after the biosolid was applied several chemical and biological soil properties such as organic C (SOC), humified C fractions (THS-C), water soluble C (DOC), total nitrogen (Nk), basal respiration (CO2-E), and potential nitrogen mineralization (PMN) increased significantly in 60 Mg ha-1 and in 90 Mg ha-1 biosolid rates. The physical soil properties studied did not change with the biosolid treatments at least in this short-term experiment. The available heavy metals showed a slight increase in the biosolid treatments but the values obtained were below those considered phytotoxic. In spite of that the canopy cover was higher in the biosolid treatment plots than in the unamended soil which will contribute to soil restoration; the analysis of the biological properties did not show such a clear trend that they could be used as soil quality indicator under the condition of this study. © 2012 Copyright Taylor and Francis Group, LLC.

It is widely accepted that conservation tillage management affords benefits to soil properties and reduces production costs; therefore these practices could be attractive to farmers from semiarid regions. The objective of this study was to assess the long-term effects of different tillage practices under semiarid conditions on macroaggregate stability (water stable aggregates, WSA), soil organic carbon (SOC), and particulate organic carbon (C-POM) content of an Alfisol from Spain. The experimental design involved a split plot and four randomized blocks in which tillage was the main factor and crop rotation (fallow-wheat-pea-barley) the secondary factor. Three tillage systems were compared no tillage (NT), minimum tillage (MT), and conventional tillage (CT). Soil samples were collected on November 2006 and October 2007. In November 2006 no significant differences in WSA were found among the tillage treatments. In October 2007, however, the mean WSA in the upper soil layer for the NT was significantly higher, 24%, that in the CT. No significant differences were seen for the subsurface layer. Under NT, the SOC and C-POM values for the surface soil layer were significantly higher than those for the other treatments on both sampling dates. At the subsurface depth, no significant differences were seen in either of these variables. The SOC and C-POM values were more homogeneous throughout the soil profile in the plowed soil than in the NT for which the corresponding values were more stratified. The results show that NT will help improve soil structure and soil fertility, which is particularly relevant to semiarid conditions like the area studied. © 2011 by the American Society of Agronomy.