Emma C. Suddick

An estimation of annual nitrous oxide emissions and soil quality following the amendment of high temperature walnut shell biochar and compost to a small scale vegetable crop rotation

Agricultural soils are responsible for emitting large quantities of nitrous oxide (N2O). The controlled incomplete thermal decomposition of agricultural wastes to produce biochar, once amended to soils, have been hypothesized to increase crop yield, improve soil quality and reduce N2O emissions. To estimate crop yields, soil quality parameters and N2O emissions following the incorporation of a high temperature (900 °C) walnut shell (HTWS) biochar into soil, a one year field campaign with four treatments (control (CONT), biochar (B), compost (COM), and biochar+compost (B+C)) was conducted in a small scale vegetable rotation system in Northern California. Crop yields from five crops (lettuce, winter cover crop, lettuce, bell pepper and Swiss chard) were determined; there were no significant differences in yield between treatments. Biochar amended soils had significant increases in % total carbon (C) and the retention of potassium (K) and calcium (Ca). Annual cumulative N2O fluxes were not significantly different between the four treatments with emissions ranging from 0.91 to 1.12 kg N2O-N ha(-1) yr(-1). Distinct peaks of N2O occurred upon the application of N fertilizers and the greatest mean emissions, ranging from 67.04 to 151.41 g N2O-N ha(-1) day(-1), were observed following the incorporation of the winter cover crop. In conclusion, HTWS biochar application to soils had a pronounced effect on the retention of exchangeable cations such as K and Ca compared to un-amended soils and composted soils, which in turn could reduce leaching of these plant available cations and could thus improve soils with poor nutrient retention. However, HTWS biochar additions to soil had neither a positive or negative effect on crop yield nor cumulative annual emissions of N2O.

The role of nitrogen in climate change and the impacts of nitrogen–climate interactions in the United States: foreword to thematic issue

Producing food, transportation, and energy for seven billion people has led to large and widespread increases in the use of synthetic nitrogen (N) fertilizers and fossil fuel combustion, resulting in a leakage of N into the environment as various forms of air and water pollution. The global N cycle is more severely altered by human activity than the global carbon (C) cycle, and reactive N dynamics affect all aspects of climate change considerations, including mitigation, adaptation, and impacts. In this special issue of Biogeochemistry, we present a review of the climate–nitrogen interactions based on a technical report for the United States National Climate Assessment presented as individual papers for terrestrial and aquatic ecosystems, agriculture and human health within the US. We provide a brief overview of each of the paper’s main points and conclusions is presented in this foreword summary.

More food, low pollution (mo fo lo Po): a grand challenge for the 21st century.

Synthetic nitrogen fertilizer has been a double-edged sword, greatly improving human nutrition during the 20th century but also posing major human health and environmental challenges for the 21st century. In August 2013, about 160 agronomists, scientists, extension agents, crop advisors, economists, social scientists, farmers, representatives of regulatory agencies and nongovernmental organizations (NGOs), and other agricultural experts gathered to discuss the vexing challenge of how to produce more food to nourish a growing population while minimizing pollution to the environment. This collection of 14 papers authored by conference participants provides a much needed analysis of the many technical, economic, and social impediments to improving nitrogen use efficiency (NUE) in crop and animal production systems. These papers demonstrate that the goals of producing more food with low pollution (Mo Fo Lo Po) will not be achieved by technological developments alone but will also require policies that recognize the economic and social factors affecting farmer decision-making. Take-home lessons from this extraordinary interdisciplinary effort include the need (i) to develop partnerships among private and public sectors to demonstrate the most current, economically feasible, best management NUE practices at local and regional scales; (ii) to improve continuing education to private sector retailers and crop advisers; (iii) to tie nutrient management to performance-based indicators on the farm and in the downwind and downstream environment; and (iv) to restore investments in research, education, extension, and human resources that are essential for developing the interdisciplinary knowledge and innovative skills needed to achieve agricultural sustainability goals.

The Potential for California Agricultural Crop Soils to Reduce Greenhouse Gas Emissions: A Holistic Evaluation

Abstract Climate change predictions for California indicate that agriculture will need to substantially adapt to reduced water availability, changing crops, and changes in temperatures, in order to sustain the level and diversity of crop production in California. California legislators recently passed the California Global Warming Solutions Act of 2006 (AB 32) that requires all industries to reduce the three major greenhouse gases (GHGs) (CO2, N2O, and CH4) to 1990 levels by 2020. The great diversity of cropping systems and management practices in California agriculture leads, however, to greater uncertainties in estimates of GHG budgets compared to Midwest agriculture. In light of AB 32, we, here, synthesize all the available information on the potentials for California agriculture to sequester C and reduce GHG emissions through various alternative management practices: minimum or no tillage, organic, cover cropping, manuring, and reduced chemical fertilizer management. Our review indicates that C sequestration and GHG emission reductions are possible, but there is no single land management practice or change in inputs that could mitigate the C released from agricultural practices (e.g., fossil fuel usage, land-use changes, soil erosion, biomass burning, and N fertilizer associated emissions) and meet climate change commitments set out in AB 32. Therefore, it is only the integration of different management strategies that shows considerable potential for C mitigation as well as provides important cobenefits to ensure the future sustainability of California agriculture.

Chapter Four – The Potential for California Agricultural Crop Soils to Reduce Greenhouse Gas Emissions: A Holistic Evaluation

Abstract Climate change predictions for California indicate that agriculture will need to substantially adapt to reduced water availability, changing crops, and changes in temperatures, in order to sustain the level and diversity of crop production in California. California legislators recently passed the California Global Warming Solutions Act of 2006 (AB 32) that requires all industries to reduce the three major greenhouse gases (GHGs) (CO2, N2O, and CH4) to 1990 levels by 2020. The great diversity of cropping systems and management practices in California agriculture leads, however, to greater uncertainties in estimates of GHG budgets compared to Midwest agriculture. In light of AB 32, we, here, synthesize all the available information on the potentials for California agriculture to sequester C and reduce GHG emissions through various alternative management practices: minimum or no tillage, organic, cover cropping, manuring, and reduced chemical fertilizer management. Our review indicates that C sequestration and GHG emission reductions are possible, but there is no single land management practice or change in inputs that could mitigate the C released from agricultural practices (e.g., fossil fuel usage, land-use changes, soil erosion, biomass burning, and N fertilizer associated emissions) and meet climate change commitments set out in AB 32. Therefore, it is only the integration of different management strategies that shows considerable potential for C mitigation as well as provides important cobenefits to ensure the future sustainability of California agriculture.

Toward a better assessment of biochar-nitrous oxide mitigation potential at the field scale

Through meta-analysis, we synthesize results from field studies on the effect of biochar application on NO emissions and crop yield. We aimed to better constrain the effect of biochar on NO emissions under field conditions, identify significant predictor variables, assess potential synergies and tradeoffs between NO mitigation and yield, and discuss knowledge gaps. The response ratios for yield and NO emissions were weighted by one of two functions: (i) the inverse of the pooled variance or (ii) the inverse of number of observations per field site. Significant emission reductions were observed when weighting by the inverse of the pooled variance (-18.1 to -7.1%) but not when weighting by the number of observations per site (-17.1 to +0.8%), thus revealing a bias in the existing data by sites with more observations. Mean yield increased by 1.7 to 13.8%. Our study shows yield benefits but no robust evidence for NO emission reductions by biochar under field conditions. When weighted by the inverse of the number of observations per site, NO emission reductions were not significantly affected by cropping system, biochar properties of feedstock, pyrolysis temperature, surface area, pH, ash content, application rate, or site characteristics of N rate, N form, or soil pH. Uneven coverage in the range of these predictor variables likely underlies the failure to detect effects. We discuss the need for future biochar field studies to investigate effects of fertilizer N form, sustained and biologically relevant changes in soil moisture, multiple biochars per site, and time since biochar application.

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.

Management to Reduce Greenhouse Gas Emissions in Western U.S. Croplands

Agriculture is a major activity in the western U.S. with approximately 57 million ha of harvested cropland of which 27% is irrigated; however, irrigated crops account for a high proportion of the economic returns because of their high economic value. We sought to summarize greenhouse gas (GHG) flux research from crop production systems in the western U.S. published from 2005 to 2011. Limited GHG emissions data were found from irrigated cropping systems in California (grain, rice, vegetable, orchards), Texas (cotton), Colorado (corn), and Washington (corn and potato), and from dryland wheat systems in Montana and North Dakota. Converting from conventional tillage (CT) to minimum-till (MT) or no-till (NT) production generally sequestered soil organic carbon (SOC) and reduced carbon dioxide (CO 2 ) emissions in many cropping systems, but not all. Methane (CH 4 ) flux was not greatly influenced by crop management practices, except in rice and manure production systems. Nitrous oxide (N 2 O) emissions were affected by N availability, climatic factors, irrigation, and crop management practices, and tended to be lower under dryland than irrigated cropping conditions. Reducing N fertilization rate and selecting the right N source can reduce N 2 O emissions as much as 50%. Use of microjet sprinkler or subsurface drip irrigation reduced N 2 O emissions in vineyards and orchards as much as 50% compared to surface drip systems. Available GHG data could be used to verify models and develop local mitigation practices, but due to the large diversity of cropping systems and ecoregions, and a lack of representative cropping system GHG databases, generalized mitigation recommendations for the western U.S. are not possible at this time.