Restricting the nonlinearity parameter in soil greenhouse gas flux calculation for more reliable flux estimates

The static chamber approach is often used for greenhouse gas (GHG) flux measurements, whereby the flux is deduced from the increase of species concentration after closing the chamber. Since this increase changes diffusion gradients between chamber air and soil air, a nonlinear increase is expected. Lateral gas flow and leakages also contribute to non linearity. Several models have been suggested to account for this non linearity, the most recent being the Hutchinson±Mosier regression model (HMR). However, the practical application of these models is challenging because the researcher needs to decide for each flux whether a nonlinear fit is appropriate or exaggerates flux estimates due to measurement artifacts. In the latter case, a flux estimate from the linear model is a more robust solution and introduces less arbitrary uncertainty to the data. We present the new, dynamic and reproducible flux calculation scheme, KAPPA.MAX, for an improved trade-off between bias and uncertainty (i.e. accuracy and precision). We develop a tool to simulate, visualise and optimise the flux calculation scheme for any specific static N2O chamber measurement system. The decision procedure and visualisation tools are implemented in a package for the R software. Finally, we demonstrate with this approach the performance of the applied flux calculation scheme for a measured flux dataset to estimate the actual bias and uncertainty. The KAPPA.MAX method effectively improved the decision between linear and nonlinear flux estimates reducing the bias at a minimal cost of uncertainty

Climate effects of recycled fertilizers and biochar: emissions of nitrous oxide, methane and ammonia in a field experiment

Background Nitrogen (N) fertilizers are essential for crop production. Farmyard manure and slurry traditionally constitute about half of the total N inputs into crop production in Switzerland. Recycled fertilizers such as biogas slurry, liquid digestates and compost enable simultaneous energy production and closing of nutrient cycles. There is evidence that recycled fertilizers can help to increase N use efficiencies and to improve N supply in organic farming. Biochar amendment has shown a potential to mitigate soil greenhouse gas (GHG) emissions, in particular nitrous oxide (N2O) emissions. Here, we combine one of the liquid recycled fertilizer treatments with biochar. In a 2.5-years on-farm experiment, we quantify GHG emissions and further gaseous N-losses via ammonia (NH3) emissions

Carbon Abatement and Emissions Associated with the Gasification of Walnut Shells for Bioenergy and Biochar Production

By converting biomass residue to biochar, we could generate power cleanly and sequester carbon resulting in overall greenhouse gas emissions (GHG) savings when compared to typical fossil fuel usage and waste disposal. We estimated the carbon dioxide (CO2) abatements and emissions associated to the concurrent production of bioenergy and biochar through biomass gasification in an organic walnut farm and processing facility in California, USA. We accounted for (i) avoided-CO2 emissions from displaced grid electricity by bioenergy; (ii) CO2 emissions from farm machinery used for soil amendment of biochar; (iii) CO2 sequestered in the soil through stable biochar-C; and (iv) direct CO2 and nitrous oxide (N2O) emissions from soil. The objective of these assessments was to pinpoint where the largest C offsets can be expected in the bioenergy-biochar chain. We found that energy production from gasification resulted in 91.8% of total C offsets, followed by stable biochar-C (8.2% of total C sinks), offsetting a total of 107.7 kg CO2-C eq Mg-1 feedstock. At the field scale, we monitored gas fluxes from soils for 29 months (180 individual observations) following field management and precipitation events in addition to weekly measurements within three growing seasons and two tree dormancy periods. We compared four treatments: control, biochar, compost, and biochar combined with compost. Biochar alone or in combination with compost did not alter total N2O and CO2 emissions from soils, indicating that under the conditions of this study, biochar-prompted C offsets may not be expected from the mitigation of direct soil GHG emissions. However, this study revealed a case where a large environmental benefit was given by the waste-to-bioenergy treatment, addressing farm level challenges such as waste management, renewable energy generation, and C sequestration

Assessing Short‐Term Impacts of Management Practices on N2O Emissions From Diverse Mediterranean Agricultural Ecosystems Using a Biogeochemical Model

Croplands are important sources of nitrous oxide (N2O) emissions. The lack of both long‐term field measurements and reliable methods for extrapolating these measurements has resulted in a large uncertainty in quantifying and mitigating N2O emissions from croplands. This is especially relevant in regions where cropping systems and farming management practices (FMPs) are diverse. In this study, a process‐based biogeochemical model, DeNitrification‐DeComposition (DNDC), was tested against N2O measurements from five cropping systems (alfalfa, wheat, lettuce, vineyards, and almond orchards) representing diverse environmental conditions and FMPs. The model tests indicated that DNDC was capable of predicting seasonal and annual total N2O emissions from these cropping systems, and the model\u27s performance was better than the Intergovernmental Panel on Climate Change emission factor approach. DNDC also captured the impacts on N2O emissions of nitrogen fertilization for wheat and lettuce, of stand age for alfalfa, as well as the spatial variability of N2O fluxes in vineyards and orchards. DNDC overestimated N2O fluxes following some heavy rainfall events. To reduce the biases of simulating N2O fluxes following heavy rainfall, studies should focus on clarifying mechanisms controlling impacts of environmental factors on denitrification. DNDC was then applied to assess the impacts on N2O emissions of FMPs, including tillage, fertilization, irrigation, and management of cover crops. The practices that can mitigate N2O emissions include reduced or no tillage, reduced N application rates, low‐volume irrigation, and cultivation of nonleguminous cover crops. This study demonstrates the necessity and potential of utilizing process‐based models to quantify N2O emissions from regions with highly diverse cropping systems

Agricultural intensification can no longer ignore water conservation – A systemic modelling approach to the case of tomato producers in Morocco

Agricultural-food production systems are facing the challenging task to provide food and socio-economic welfare while preserving natural resources in the long-term. In Morocco, the Green Moroccan Plan steered the promotion of groundwater-based drip irrigation. Over the last decade, the Plan encouraged producers to shift to cash crop production. This is how tomato became a main agri-food export commodity mostly produced in greenhouses in the Souss-Massa region and produced intensively in open-fields for local demand in the Northern part of the country. However, water resources are expected to become particularly scarce over the next decades, increasing the vulnerabilities of tomato farmers in face of unforeseen changes and shocks. The main purpose of this study is to show a) how global and local tomato value chains respond to irrigation schemes and b) what the environmental consequences are. By means of a system dynamics model, and a survey conducted among a sample of 244 producers, we describe and outline the major interactions between agricultural, ecological and socio-economic dimensions of the tomato production systems. The results of the model simulations highlight how overexploitation of groundwater tables negatively affects crop production and farmers’ welfare. The model shows that in the near future, water scarcity will have long-lasting consequences on the producers, such as reduced productivity and losses in cash flow. Our model results highlight that measures need to be taken in the coming years in order to prevent the predicted irremediable water shortage in 2030. We conclude that the current groundwater management will, in the long-term, lead to irreversible groundwater depletion which will enhance already existing inequalities between the two types of producers. Urgent actions have to be taken in order to sustainably manage water while supporting farmers in the long-term.publishedVersio

Neoformation of soil aggregates after a volcano eruption in meadows of Northern Patagonia, Argentina

In June 2011, a natural event occurred in Patagonia, Argentina: The “Puyehue-Cordón Caulle” volcanic complex erupted, and particles from tephras (1-5cm) to very fine volcanic ash (44-500?m) where deposited in the direction of prevailing winds (West to East). The ash was biologically inert, with no organic compounds, neutral pH and low electrical conductivity. The objective was to study neoformation processes of soil aggregates in wet meadows after volcano eruptionEstación Experimental Agropecuaria BarilocheFil: Enriquez, Andrea Soledad. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Cremona, María Victoria. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; ArgentinaFil: Six, Johan. Escuela Politécnica Federal de Zurich; Suiz

No Till and Organic Farming Improve Soil Properties but Reduce Crop Yield Compared to Conventional Farming in a Swiss Farm Network

Soils are of vital importance for sustainable food production. In order to maintain or improve soil quality, it is necessary to develop strategies for a sustainable use of soil. Alternative cropping practices such as reduced tillage and improved crop rotation are more and more adopted with the aim of decreasing the impact of agriculture on the environment. However, their on-the-ground impact in Swiss farming systems still has to be assessed. In this study, we quantified the impact of three farming systems (conventional farming, no-till, and organic farming) on plant and soil chemical, biological and physical properties. Our study included 20 fields for each farming system. All selected fields were cultivated with winter wheat the year of sampling. Soil was sampled at four layers, 0-5 cm, 5-20 cm, 20-25 cm, 25-50 cm. The main variables analysed were grain yield, soil nutrient availability, organic carbon stocks, bulk density, aggregation, porosity and soil biology. This was complemented with a comprehensive survey to collect information about cropping practices at field and farm scale, including organic matter inputs, fertilisation, tillage, phytosanitary treatments, and crop rotation.Our results show a significant influence of cropping practices on plant and soil properties. Wheat yield in no till and organic systems was reduced by 10% and 30% compared to conventional systems. Bulk density was higher in no-till than in ploughed fields in the 5-20 cm layer but similar in the subsoil. A strong stratification with depth of nutrients and soil organic carbon was observed in no-till fields. No-till and organic fields showed larger soil aggregates and higher microbial biomass in the surface layer (0-5 cm). Mycorrhizal colonisation of wheat roots was on average 50% higher in organic fields. However, no differences in carbon stock in the 0-20 cm layer was observed and the ratio organic matter / clay shows a high variability (from poor to good) and was not dependent on the farming system.Our results show that an improvement of soil properties can be achieved with alternative cropping practices such as no-till and organic farming, but also depends on the other practices adopted by the farmers, such as input of organic amendments, crop rotation diversification, residue management

Transdisciplinary systems research to develop a holistic approach to reduce the spread and impact of cocoa swollen shoot virus disease in Ghana (TransdisCSSVD)

West Africa is the world’s most important cocoa (Theobroma cacao L.) growing region. The Cocoa Swollen Shoot Virus Disease (CSSVD) is one of the major productivity limitations, particularly in Ghana. Some 800’000 farm families’ livelihoods depend on revenues from the crop in Ghana alone. The only measure to treat CSSVD is to cut out infected trees. The national eradication program, implemented by the Ghanaian government since 1946, has cut out more than 250 million trees until today. Despite these efforts, CSSVD is still prevalent in the field. Research has tried to contribute to CSSVD control through breeding for resistant varieties, as well as investigating the effects of barriers with immune crops and protection through a “vaccination” with the mild virus strain N1. Despite the promising nature of the results from these research activities, they have seen limited application in the field. Therefore, a shift in approaches is needed: farmers, extension agents and other relevant stakeholders need to be involved in planning and execution of future interventions from the very beginning of project life cycles. We are starting a project called “TransdisCSSVD” in Ghana, which approaches disease control by capitalizing on the farmers’ perspective on CSSVD control in order to identify the main bottlenecks for implementation of available CSSVD control options. Furthermore, an in-depth study on diversification of cocoa production systems (e.g. agroforestry; fragmentation of landscapes by barriers of non-host crops, shrubs or trees; etc.) will fill an important knowledge gap with regard to CSSVD regulation. The expected results may provide crucial insights for policy makers about meaningful ways of adapting the existing CSSVD prevention and control program. For that purpose, transdisciplinary workshops with policymakers are planned. More dissemination activities such as farmer field days and exchange workshops aim at stimulating the implementation of research results on the ground