This paper reviews the technological and economical feasibilities as well as sustainable assessment of approaches (thermochemical and biochemical) applied for sustainable “drop-in” fuel production from lignocellulosic sources. The challenges for each pathway to produce “drop-in” fuels are covered. Currently “drop-in” fuel production cost is approximately 2 times (~5–6$/gallon) higher than fossil fuels (3$/gallon), especially with the use of 2nd generation feedstocks. The primary sources of cost with “drop-in” fuel production are feedstock cost (40–60% of the total production cost), syngas cleaning and conditioning to meet Fischer-Tropsch synthesis requirement (12–15% of the total production cost) and bio oil upgrading (14–18% of the total production cost) in the case of pyrolysis and hydrothermal liquefaction (HTL). The most influential factors on the life cycle analysis (LCA) were biomass cultivation, harvesting, biomass pre-treatment, and transportation. Therefore, robust processes that can use local waste biomass are far more environmental and economically viable, especially as biofuel from second generation have a greater potential to reduce greenhouse gas emissions (50–100%) than first generation biofuels (50–90%) when land use changes are omitted in the LCA. The sustainability of biofuels is pre-dominantly dependant on the sustainability of the initial biomass, with 2nd generation feedstocks being more sustainable than 1st generation. Gasification-FTS is considered as the most promising technique for “drop-in” fuel production over pyrolysis and HTL due to its flexibility towards feedstock acceptance and the ability to produced high yields of liquid fuel together with other economically viable biofuels such as electricity and heat. Biochemical routes (i.e.fermentation) to “drop-in” fuels are still in their early development stages, and therefore require more studies and pilot-scale experiments in order to discover an economic and sustainable means of using these methods.

“Drop-in” fuel production from biomass: Critical review on techno-economic feasibility and sustainability

A healthy soil acts as a dynamic living system that delivers multiple ecosystem services, such as sustaining water quality and plant productivity, controlling soil nutrient recycling decomposition, and removing greenhouse gases from the atmosphere. Soil health is closely associated with sustainable agriculture, because soil microorganism diversity and activity are the main components of soil health. Agricultural sustainability is defined as the ability of a crop production system to continuously produce food without environmental degradation. Arbuscular mycorrhizal fungi (AMF), cyanobacteria, and beneficial nematodes enhance water use efficiency and nutrient availability to plants, phytohormones production, soil nutrient cycling, and plant resistance to environmental stresses. Farming practices have shown that organic farming and tillage improve soil health by increasing the abundance, diversity, and activity of microorganisms. Conservation tillage can potentially increase grower’s profitability by reducing inputs and labor costs as compared to conventional tillage while organic farming might add extra management costs due to high labor demands for weeding and pest control, and for fertilizer inputs (particularly N-based), which typically have less consistent uniformity and stability than synthetic fertilizers. This review will discuss the external factors controlling the abundance of rhizosphere microbiota and the impact of crop management practices on soil health and their role in sustainable crop production.

Soil Health and Sustainable Agriculture

Comparing the effects of soil fauna on litter decomposition and organic matter turnover in sustainably and conventionally managed olive orchards

Agriculture is the foundation of social development. Under the pressure of population growth, natural disasters, environmental pollution, climate change, and food safety, the interdisciplinary "new agriculture" is becoming an important trend of modern agriculture. In fact, new agriculture is not only the foundation of great health and new energy sources, but is also the cornerstone of national food security, energy security, and biosafety. Hydrogen agronomy focuses mainly on the mechanism of hydrogen gas (H2) biology effects in agriculture, and provides a theoretical foundation for the practice of hydrogen agriculture, a component of the new agriculture. Previous research on the biological effects of H2 focused chiefly on medicine. The mechanism of selective antioxidant is the main theoretical basis of hydrogen medicine. Subsequent experiments have demonstrated that H2 can regulate the growth and development of plant crops, edible fungus, and livestock, and enhance the tolerance of these agriculturally important organisms against abiotic and biotic stresses. Even more importantly, H2 can regulate the growth and development of crops by changing the soil microbial community composition and structure. Use of H2 can also improve the nutritional value and postharvest quality of agricultural products. Researchers have also shown that the biological functions of molecular hydrogen are mediated by modulating reactive oxygen species (ROS), nitric oxide (NO), and carbon monoxide (CO) signaling cascades in plants and microbes. This review summarizes and clarifies the history of hydrogen agronomy and describes recent progress in the field. We also argue that emerging hydrogen agriculture will be an important direction in the new agriculture. Further, we discuss several scientific problems in hydrogen agronomy, and suggest that the future of hydrogen agronomy depends on contributions by multiple disciplines. Important future research directions of hydrogen agronomy include hydrogen agriculture in special environments, such as islands, reefs, aircraft, and outer space.

Hydrogen agronomy: research progress and prospects.

Sustainability is critical for biomass feedstock supply and crop production. Most studies on agricultural residue estimations ignored the loss of soil organic carbon (SOC) and thus possibly overestimated its resource potential. This study estimated the resource potential of using agricultural residues for bioenergy in China, considering soil conservation, collection cost, and future changes in yield and management. This study carried out a spatial explicit assessment of sustainable agricultural residue potential and their on-farm collection costs. Rothamsted carbon model was used to quantify the grid-specific amount of residue to be retained in soil for sustainable purposes. The results showed that 226 Mt of residues could be collected annually to maintain the current SOC level, which ranges from 0.1% to 39.0% at a mean of 1.1% nationwide. To achieve SOC level above 2% over all arable land in China, the collectable residues would be reduced to 24 Mt. Future yield improvements and no-tillage would significantly increase the collectable residues to 117, 383, and 514 Mt in 2050 under SOC scenarios of above 2%, above 1%, and maintaining current level, respectively. Maintaining the current SOC level, 495 Mt of residues could be collected in 2050 with a cost ≤ 0.98 $⋅GJ−1, which equals 8.6 EJ of energy potential. From the view of high supply potentials and low collection costs, Shandong, Henan, and Jiangsu provinces are the preferred regions to develop residue-based bioenergy production. The results highlighted the differences of resource potential among various SOC scenarios and spatial heterogeneity of residue resource among regions.

Spatially explicit analyses of sustainable agricultural residue potential for bioenergy in China under various soil and land management scenarios

Tillage and residue management drive rapid changes in soil macrofauna communities and soil properties in a semiarid cropping system of Eastern Colorado

Daniel A. Melman

Papers

Tillage and residue management drive rapid changes in soil macrofauna communities and soil properties in a semiarid cropping system of Eastern Colorado