Modeling Soil Organic Carbon Changes under Alternative Climatic Scenarios and Soil Properties Using DNDC Model at a Semi-Arid Mediterranean Environment

Soil organic carbon (SOC) is one of the central issues in dealing with soil fertility as well as environmental and food safety. Due to the lack of relevant data sources and methodologies, analyzing SOC dynamics has been a challenge in Morocco. During the last two decades, processbased models have been adopted as alternative and powerful tools for modeling SOC dynamics; whereas, information and knowledge on the most sensitive model inputs under different climate, and soil conditions are still very limited. For this purpose, a sensitivity analysis was conducted in the present work, using the DeNitrification-DeComposition (DNDC) model based on the data collected at a semi-arid region (Merchouch station, Morocco). The objective is to identify the most influential factors affecting the DNDC-modeled SOC dynamics in a semi-arid region across different climatic and soil conditions. The results of sensitivity analysis highlighted air temperature as the main determinant of SOC. A decrease in air temperature of 4 C results in an almost 161 kg C ha?1 yr?1 increase in C sequestration rate. Initial SOC was also confirmed to be one of the most sensitive parameters for SOC. There was a 96 kg C ha?1 yr?1 increase in C sequestration rate under low initial SOC (0.005 kg C ha?1). In the DNDC, air temperature in climatic factors and initial SOC in variable soil properties had the largest impacts on SOC accumulation in Merchouch station. We can conclude that the sensitivity analysis conducted in this study within the DNDC can contribute to provide a scientific evidence of uncertainties of the selected inputs variables who can lead to uncertainties on the SOC in the study site. The information in this paper can be helpful for scientists and policy makers, who are dealing with regions of similar environmental conditions as Merchouch Station, by identifying alternative scenarios of soil carbon sequestration

Factors That Influence Nitrous Oxide Emissions from Agricultural Soils as Well as Their Representation in Simulation Models: A Review

Nitrous oxide (N2O) is a long-lived greenhouse gas that contributes to global warming. Emissions of N2O mainly stem from agricultural soils. This review highlights the principal factors from peer-reviewed literature affecting N2O emissions from agricultural soils, by grouping the factors into three categories: environmental, management and measurement. Within these categories, each impact factor is explained in detail and its influence on N2O emissions from the soil is summarized. It is also shown how each impact factor influences other impact factors. Process-based simulation models used for estimating N2O emissions are reviewed regarding their ability to consider the impact factors in simulating N2O. The model strengths and weaknesses in simulating N2O emissions from managed soils are summarized. Finally, three selected process-based simulation models (Daily Century (DAYCENT), DeNitrification-DeComposition (DNDC), and Soil and Water Assessment Tool (SWAT)) are discussed that are widely used to simulate N2O emissions from cropping systems. Their ability to simulate N2O emissions is evaluated by describing the model components that are relevant to N2O processes and their representation in the model

A comparison of methods to quantify greenhouse gas emissions of cropping systems in LCA

Carbon dioxide and nitrous oxide are two important greenhouse gases (GHG) released from cropping systems. Their emissions can vary substantially with climate, soil, and crop management. While different methods are available to account for GHG emissions in life cycle assessments (LCA) of crop production, there are no standard procedures. In this study, the objectives were: (i) to compare several methods of estimating CO2 and N2O emissions for a LCA of cropping systems and (ii) to estimate the relative contribution of soil GHG emissions to the overall global warming potential (GWP) using results from a field experiment located in Manitoba, Canada. The methods were: (A) measurements; (B) Tier I and (C) Tier II IPCC (Intergovernmental panel on Climate Change) methodology, (D) a simple carbon model combined with Intergovernmental Panel for Climate Change (IPCC) Tier II methodology for soil N2O emissions, and (E) the DNDC (DeNitrification DeComposition) agroecosystem model. The estimated GWPs (−7.2–17 Mg CO2eq ha−1 y−1; −80 to 600 kg CO2eq GJ−1 y−1) were similar to previous results in North America and no statistical difference was found between GWP based on methods D and E and GWP based on observations. The five methods gave estimates of soil CO2 emissions that were not statistically different from each other, whereas for N2O emissions only DNDC estimates were similar to observations. Across crop types, all methods gave comparable CO2 and N2O emission estimates for perennial and legume crops, but only DNDC gave similar results with respect to observations for both annual and cereal crops. Whilst the results should be confirmed for other locations, the agroecosystem model and method D can be used, at certainly one selected site, in place of observations for estimating GHGs in agricultural LCA

Digitization of crop nitrogen modelling: A review

Applying the correct dose of nitrogen (N) fertilizer to crops is extremely important. The current predictive models of yield and soil–crop dynamics during the crop growing season currently combine information about soil, climate, crops, and agricultural practices to predict the N needs of plants and optimize its application. Recent advances in remote sensing technology have also contributed to digital modelling of crop N requirements. These sensors provide detailed data, allowing for real-time adjustments in order to increase nutrient application accuracy. Combining these with other tools such as geographic information systems, data analysis, and their integration in modelling with experimental approaches in techniques such as machine learning (ML) and artificial intelligence, it is possible to develop digital twins for complex agricultural systems. Creating digital twins from the physical field can simulate the impact of different events and actions. In this article, we review the state-of-the-art of modelling N needs by crops, starting by exploring N dynamics in the soil−plant system; we demonstrate different classical approaches to modelling these dynamics so as to predict the needs and to define the optimal fertilization doses of this nutrient. Therefore, this article reviews the currently available information from Google Scholar and ScienceDirect, using relevant studies on N dynamics in agricultural systems, different modelling approaches used to simulate crop growth and N dynamics, and the application of digital tools and technologies for modelling proposed crops. The cited articles were selected following the exclusion criteria, resulting in a total of 66 articles. Finally, we present digital tools and technologies that increase the accuracy of model estimates and improve the simulation and presentation of estimated results to the manager in order to facilitate decision-making processes

Managing seasonal soil nitrogen dynamics in inland valleys of the West African savanna zone

Most cropping systems in the Dry Savanna agro-ecological zone of West Africa qualify as low-input systems. Nitrogen is the most limiting nutrient element and the prevailing low-input systems rely mainly on the provision of native soil N. Depending on environmental conditions and management practices, the process of soil N mineralization not only provides N for crop nutrition but can also entail substantial N losses. Alternate soil drying and wetting cycles and seasonal changes in the rainfall intensity reportedly affect soil N dynamics and nitrate-N can be lost by leaching and denitrification, mainly during the dry-to-wet season transition period (DWT). Besides such temporal dynamics, soil N in the undulating inland valley landscape of West Africa is also subject to spatial fluxes and translocation of water and nitrate along the toposequence. This may exacerbate the intensity of nitrate dynamics in the bottomlands, used for producing rainfed lowland rice. Managing soil native N by avoiding losses during DWT is key for crop productivity in the short-term and to maintain soil fertility in long-term. Field experiments were conducted in Burkina Faso and Benin in 2013 and 2014 to quantify the intensity and dynamics and to evaluate options for managing seasonal soil nitrate-N in inland valleys of the Dry Savanna zone. In addition, the effects of rainfall intensity and soil tillage were assessed. With the onset of the first rains, mineralization processes lead to an accumulation of nitrate-N ha-1 in the topsoil of which 10-15 kg were translocated by subsurface flows to the valley bottom wetland. Thus nitrate influxes had little effects on the performance of rice in the valley bottom, indicating the occurrence of substantial N losses. The integration of transition season crops in the lowland could capture and temporarily immobilize soil N, reducing the extractable soil nitrate content to 8-25 from 50-75 kg N ha-1 in the bare fallow control treatment. Nitrate-catching vegetation effectively reduced the build-up of native soil Nmin, thus potentially reducing nitrate-N losses and, upon biomass incorporation, enhanced the productivity of wet season rainfed rice with grain yield increases of 1-2 t ha-1 above the bare fallow control (1.7 t ha-1). The extent of such effects strongly depended on soil tillage and rainfall amounts. Thus, soil tillage tended to increase N mineralization and the extent of the nitrate peak during DWT. While a 30% reduced rainfall during DWT increased the nitrate accumulation, the absence of drastic changes in soil aeration status limited apparent nitrate losses. On the other hand, a 30% increased rainfall during DWT lead to a rapid soil saturation and little nitrate remained once the volumetric soil moisture exceeded 25%. The reported finding point to the need for management approaches that contribute to conserve native soil N for enhancing lowland rice production, such as nitrate-catching vegetation during DWT. The targeting of such approaches, however, is highly site specific and their relevance and effectiveness will depend on projected climate change.Management der saisonalen Dynamik von Boden-Stickstoff in Inlandtälern der westafrikanischen Savanne Die meisten Produktionssysteme in der Trockensavanne Westafrikas sind durch geringen Einsatz externer Produktionsmittel gekennzeichnet. Gerade in „low-input“ Systemen ist Stickstoffmangel weit verbreitet und die N-Versorgung der Kulturpflanzen basiert im Wesentlichen auf die Nachlieferung aus Bodenvorräten. Je nach Umweltbedingung und Managementsystem trägt die Mineralisierung von Boden-N aber nicht nur zur Nährstoffversorgung der Kulturen bei, sie kann auch zu erheblichen N-Verlusten führen. Gerade wiederholte Zyklen von Austrocknung und Wiederbefeuchten des Bodens sowie saisonale Schwankungen in Niederschlagsintensität und –verteilung kann nachweislich die Boden-N-Dynamik beeinflussen, vor allem in der Übergangsperiode zwischen Trocken- und Regenzeit. Neben solchen zeitlichen Dynamiken ist Nitrate auch räumlich mobil und führt in der Landschaft von Inlandtälern zu vertikalen wie auch horizontalen Nitrat-Flüssen entlang der Catena, Das Management dieser Nitratdynamik und die Vermeidung von N-Verlusten während der Übergangsperiode ist somit kurzfristig der Schlüssel für steigende Erträge. Feldversuche wurden 2013 und 2014 in Burkina Faso und Benin durchgeführt, um die Intensität und die Dynamik der Boden-N Mineralisierung während der Übergangsperiode zu quantifizieren und Management-Optionen hinsichtlich ihrer Bedeutung zur Verminderung von N-Verlusten und zur Ertragssteigerung von Nassreis vergleichend zu bewerten. Zudem wurde die Bedeutung der Niederschlagsmenge und der Bodenbearbeitung auf die saisonale Boden-N-Dynamik ermittelt. Mit Einsetzen der ersten Regenfälle konnte eine N Anreichung im Oberboden nachgewiesen werden, wovon 10-15 kg Nitrat-N vom Hang in die Talsohle verlagert wurden, was sich allerdings nicht signifikant im Reisertrag niederschlug. Diese Beobachtung stützt die Vermutung, dass die substantiellen Mengen an Nitrat im saturierten Boden der Talsohle verloren gingen. Der Anbau einer Zwischenfrucht während der Übergangsperiode vermochte Nitrat aufzunehmen, und somit die verfügbare Nitratmenge von etwa 50 kg/ha in der Nacktbrache auf 8-25 kg/ha zu reduzieren. Der Erhalt von Boden-N sowie die zusätzliche Zufuhr von atmosphärischen N2 über die Stickstoffbindung vermochte die Reiskornerträge um 1-2 t/ha über die Kontrollparzelle zu erhöhen. Das Ausmaß solcher Effekte differierte allerdings in Abhängigkeit der Niederschlagsmenge sowie der Art der Bodenbearbeitung. Eine wendende Bodenbearbeitung stimulierte die N-Mineralisierung am Hang und erhöhte somit die lateralen Einträge von Nitrat in die Talsohle. Eine 30%ige Verminderung der Niederschlagsmenge während der Übergangsperiode erhöhte die Nitrat-Anreicherung im Oberboden, reduzierte aber Nitratverluste. Umgekehrt erhöhte eine 30%ige Erhöhung der Niederschläge die Nitrat-Verluste drastisch. Die vorgelegten Ergebnisse unterstreichen den Bedarf für ein verbessertes Management des Boden-N, speziell in der kritischen Übergangsphase zwischen Trocken- und Regenzeit. Der Anbau von Zwischenfrüchten vermochte so Boden-N zu konservieren und Reiserträge nachweislich zu steigern. Die Relevanz und die Effektivität solcher Ansätze hängt im Wesentlichen vom der Intensität des Wechsels der Bodenbelüftung ab und ist somit hochgradig Standort-spezifisch. Die künftige Entwicklung des Klimawandels wird folglich entscheidend für die Ausweisung von Extrapolations-Domänen der Technologie-Optionen sein

Crop production, water pollution, or climate change mitigation—Which drives socially optimal fertilization management most?

We introduce a multistep modeling approach for studying optimal management of fertilizer inputs in a situation where soil nitrogen and carbon dynamics and water and atmosphere externalities are considered. The three steps in the modeling process are: (1) generation of the data sets with a detailed simulation model; (2) estimation of the system models from the data; (3) application of the obtained dynamic economic optimization model considering inorganic and organic fertilizer inputs. We demonstrate the approach with a case study: barley production in southern Finland on coarse and clay soils. Our results show that there is a synergy between climate change mitigation and water protection goals, and a trade-off between pollution mitigation and crop production goals. If a field is a significant source of greenhouse gas (GHG) emissions and an insignificant source of water pollution, atmospheric externalities dominate the water externalities, even for a relatively low social cost of carbon (SCC). If a field is a significant source of water pollution, the SCC would have to be very high before atmospheric externalities dominate water externalities. In addition, an integrated nutrient management system appears better than a system in which only inorganic or organic fertilizer is used, although manure is not a solution to agriculture's GHG emissions problem. Moreover, GHG emissions and nitrogen and carbon leaching mitigation efforts should first be targeted at coarse soils rather than clay soils, because the marginal abatement costs are considerably lower for coarse soils.Peer reviewe

Sustainable Cropping Systems

Global crop production must substantially increase to meet the needs of a rapidly growing population. This is constrained by the availability of nutrients, water, and land. There is also an urgent need to reduce the negative environmental impacts of crop production. Collectively, these issues represent one of the greatest challenges of the twenty-first century. Sustainable cropping systems based on ecological principles are the core of integrated approaches to solve this critical challenge. This special issue provides an international basis for revealing the underlying mechanisms of sustainable cropping systems to drive agronomic innovations. It includes review and original research articles that report novel scientific findings on improvement in cropping systems related to crop yields and their resistance to biotic and abiotic stressors, resource use efficiency, environmental impact, sustainability, and ecosystem services

Modelling spatial variation and environmental impacts of land use change in the exploitation of land-based renewable bioenergy crops

Spatial factors are of particular importance to the sustainability of land based energy crops, due both to the need to minimise feedstock transport, and to the importance of cultivation site attributes in determining key environmental impacts. This study uses geographical information system (GIS) mapping to identify sites suitable for the cultivation of Miscanthus or short rotation coppiced (SRC) SRC willow for co-firing with coal or generation of combined heat and power (CHP). Modelling using an adapted version of DayCent was performed for typical sites to assess variation in yield, nitrous oxide (N2O) emissions, evapotranspiration (ET) and change in soil organic carbon (SOC) according to soil properties, hydrologic regime and previous land use. Development of the DayCent model as part of this research gave improved simulation of the impacts of tillage on soil porosity, and resultant N2O emissions from soil, and improved simulation of growth of SRC willow following coppicing management, leading to improved yield predictions. For land use change from arable to perennial cultivation, increased SOC was simulated, along with reduced N2O emissions, particularly on soils prone to anoxia. However, in general, benefits of cultivation of Miscanthus and SRC willow for energy are maximised when the crops are grown at sites where high yields are achieved, and used to generate CHP, since this minimises the land area required per unit energy generated. Further model development work and additional field data for model verification are necessary for firmer conclusions on the change in net greenhouse gas (GHG) emissions following land use change. Additionally, indirect land use change may negate perceived benefits, and locations are difficult to predict or identify in a complex global system. Given the magnitude of identified variations in yields and changes in N2O emissions, spatial variation in benefits of bioenergy cultivation should be a factor in decisions to provide economic support for cultivation. However, calculations suggest that emissions offset by replacing energy generation from fossil fuels may have greater impact on GHG savings per gigajoule (GJ) than cultivation site attributes. Since total energy conversion efficiency may be in the region of 30% for electricity-only generation and up to 90% for CHP generation, planning feedstock supply chains to maximise efficiency of feedstock end use is therefore beneficial

SOIL MANAGEMENT AND NITROGEN DYNAMICS IN BURLEY TOBACCO ROTATIONS

Agronomic practices, including tillage, crop rotation and N fertilization, have been developed to efficiently manage soil N dynamics and crop N nutrition. These practices can affect soil organic carbon (SOC) and soil total nitrogen (STN) sequestration, and consequently influence soil nitrogen mineralization (SNM) and crop N nutrition. However, little research has been systematically and simultaneously conducted to examine the effect of agronomic management on (1) SOC and STN stocks; (2) SNM; and (3) crop N nutrition. Burley tobacco (Nicotiana tobacum L.) is a N demanding crop and subject to inefficiency in N fertilization. Moreover, conservation tillage and rotation have been integrated into traditionally tillage intensive tobacco cropping systems. Thus, a tobacco tillage and rotation study was used to test how agronomic practices can affect N dynamics and crop N status in a series of sequential experiments. Firstly, different tobacco production systems were utilized to investigate the effects of tillage and rotation on soil aggregate stabilization and associated SOM sequestration. No-tillage and rotation management enhanced SOC and STN stocks, mainly by increasing the proportion of macroaggregates and SOC and STN concentrations. Secondly, a series of studies were conducted on SNM, including: (1) comparison of laboratory and in situ resin-core methods in estimating SNM; (2) evaluation of the influence of N fertilizer application on SNM; and (3) comparison of chemical indices for predicting SNM across management treatments over time. Laboratory method had different results relative to in situ method due to sample pretreatments. Fertilizer N application had a priming effect on SNM, but priming depended on both the N fertilizer rate and the background SOM level. The effect of rotation/tillage treatments on SNM was stable across years and SOC appeared to be the best indicator of SNM among other soil carbon and N estimates. Thirdly, a N fertilizer study for different tillage systems was conducted in 2012 and 2013. Crop parameters and plant available N (PAN) were collected to investigate the impact of tillage on tobacco production. Crop parameters showed that no-tillage can result in N deficiency in dry years. Similar PAN for both tillage methods suggested N deficiency in no-till tobacco was due to the crop’s lower N uptake capacity. In 2014, tobacco root analysis confirmed that no-tillage can result in less root exploration of the soil volume than conventional tillage