• Authors:
    • Pereira,E. I. P.
    • Suddick,E. C.
    • Mansour,I.
    • Mukome,F. N. D.
    • Parikh,S. J.
    • Scow,K.
    • Six,J.
  • Source: Biology and Fertility of Soils
  • Volume: 51
  • Issue: 5
  • Year: 2015
  • Summary: We investigated the effect of biochar type on plant performance and soil nitrogen (N) transformations in mesocosms representing an organic lettuce ( Lactuca sativa) production system. Five biochar materials were added to a silt loam soil: Douglas fir wood pyrolyzed at 410°C (W410), Douglas fir wood pyrolyzed at 510°C (W510), pine chip pyrolyzed at 550°C (PC), hogwaste wood pyrolyzed between 600 and 700°C (SWC), and walnut shell gasified at 900°C (WS). Soil pH and cation exchange capacity were significantly increased by WS biochar only. Gross mineralization increased in response to biochar materials with high H/C ratio (i.e., W410, W510, and SWC), which can be favorable for organic farming systems challenged by insufficient N mineralization during plant growth. Net nitrification was increased by W510, PC, and WS without correlating with the abundance of ammonia oxidizing gene ( amoA). Increases in N transformation rates did not translate into increases in plant productivity or leaf N content. WS biochar increased the abundance of amoA and nitrite reductase gene ( nirK), while SWC biochar decreased the abundance of amoA and nitrous oxide gene ( nosZ). Decreases in N 2O emissions were only observed in soil amended with W510 for 3 days out of the 42-day growing season without affecting total cumulative N 2O fluxes. This suggests that effects of biochar on decreasing N 2O emissions may be transient, which compromise biochar's potential to be used as a N 2O mitigation strategy in organic systems. Overall, our results confirm that different biochar materials can distinctively affect soil properties and N turnover.
  • Authors:
    • Strzepek,K.
    • Neumann,J.
    • Smith,J.
    • Martinich,J.
    • Boehlert,B.
    • Hejazi,M.
    • Henderson,J.
    • Wobus,C.
    • Jones,R.
    • Calvin,K.
    • Johnson,D.
    • Monier,E.
    • Strzepek,J.
    • Yoon,J. -H
  • Source: Climatic Change
  • Volume: 131
  • Issue: 1
  • Year: 2015
  • Summary: Climate change impacts on water resources in the United States are likely to be far-reaching and substantial because the water is integral to climate, and the water sector spans many parts of the economy. This paper estimates impacts and damages from five water resource-related models addressing runoff, drought risk, economics of water supply/demand, water stress, and flooding damages. The models differ in the water system assessed, spatial scale, and unit of assessment, but together provide a quantitative and descriptive richness in characterizing water sector effects that no single model can capture. The results, driven by a consistent set of greenhouse gas (GHG) emission and climate scenarios, examine uncertainty from emissions, climate sensitivity, and climate model selection. While calculating the net impact of climate change on the water sector as a whole may be impractical, broad conclusions can be drawn regarding patterns of change and benefits of GHG mitigation. Four key findings emerge: 1) GHG mitigation substantially reduces hydro-climatic impacts on the water sector; 2) GHG mitigation provides substantial national economic benefits in water resources related sectors; 3) the models show a strong signal of wetting for the Eastern US and a strong signal of drying in the Southwest; and 4) unmanaged hydrologic systems impacts show strong correlation with the change in magnitude and direction of precipitation and temperature from climate models, but managed water resource systems and regional economic systems show lower correlation with changes in climate variables due to non-linearities created by water infrastructure and the socio-economic changes in non-climate driven water demand.
  • Authors:
    • Wise,M.
    • Hodson,E. L.
    • Mignone,B. K.
    • Clarke,L.
    • Waldhoff,S.
    • Luckow,P.
  • Source: Energy Economics
  • Volume: 50
  • Year: 2015
  • Summary: Accurately characterizing the emissions implications of bioenergy is increasingly important to the design of regional and global greenhouse gas mitigation policies. Market-based policies, in particular, often use information about carbon intensity to adjust relative deployment incentives for different energy sources. However, the carbon intensity of bioenergy is difficult to quantify because carbon emissions can occur when land use changes to expand production of bioenergy crops rather than simply when the fuel is consumed as for fossil fuels. Using a long-term, integrated assessment model, this paper develops an approach for computing the carbon intensity of bioenergy production that isolates the marginal impact of increasing production of a specific bioenergy crop in a specific region, taking into account economic competition among land uses. We explore several factors that affect emissions intensity and explain these results in the context of previous studies that use different approaches. Among the factors explored, our results suggest that the carbon intensity of bioenergy production from land use change (LUC) differs by a factor of two depending on the region in which the bioenergy crop is grown in the United States. Assumptions about international land use policies (such as those related to forest protection) and crop yields also significantly impact carbon intensity. Finally, we develop and demonstrate a generalized method for considering the varying time profile of LUC emissions from bioenergy production, taking into account the time path of future carbon prices, the discount rate and the time horizon. When evaluated in the context of power sector applications, we found electricity from bioenergy crops to be less carbon-intensive than conventional coal-fired electricity generation and often less carbon-intensive than natural-gas fired generation. © 2015 Elsevier B.V.
  • Authors:
    • Zhang HengHeng
    • Yan ChangRong
    • Zhang YanQing
    • Wang JianBo
    • He WenQing
    • Chen BaoQing
    • Liu EnKe
  • Source: Transactions of the Chinese Society of Agricultural Engineering
  • Volume: 31
  • Issue: 4
  • Year: 2015
  • Summary: Soil conservation tillage practices such as no-tillage and straw mulching are of great significance for saving energy input in farmland, mitigating greenhouse gas emission to the atmosphere, and increasing carbon sequestration potential in soils. Despite of great interest in the effect of no-tillage (NT) management practice on carbon sequestration and GHG emissions in northern China, long-term effects of different tillage practices in that region on farmland system carbon footprints remain unclear. Based on a 20-year conservation tillage experiment in a winter wheat system at Linfen City in Shanxi province, we evaluated long-term (20-year) effects of NT and conventional tillage (CT) practices on the carbon balance. During the experiment, we measured soil respiration and soil carbon concentration in the field. A random block design with three replications was used to assess both the tillage and its effects on soil carbon sequestration and yield of winter wheat ( Triticum aestivum L.). Production, formulation, storage, and distribution of these inputs such as seed, chemical fertilizer and application with tractor equipment cause the combustion of fossil fuel and use of energy from other sources, which also emits CO 2 and other GHGs into the atmosphere. Thus, it is essential to understand emissions in kilograms carbon equivalent (kg CE) of various tillage operations, fertilizers, pesticides, harvesting and residue management. The index of carbon emission of different agricultural inputs were taken from literatures. In our study, carbon emission produced by chemical fertilizer with NT and CT practices accounted for 73.3%-77.1% of total carbon emission from agricultural inputs, and has become the main carbon source. Compared with other countries, fertilizer input in China accounts for a greater portion within agricultural production, and fertilizer costs made up about 50% of total costs in china. Reducing fertilizer use is an effective means to decrease indirect carbon emission. Because NT reduced moldboard ploughing, chisel ploughing and stover removal, carbon emission from agricultural inputs under NT was 5.1% less than that under CT. Moreover, T. aestivum L. yield with NT treatment increased by 28.9% over CT treatment. Carbon productivity in the NT system was greater than that in CT. After 20 years, SOC concentration in NT soil was greater than that in the CT soil, but only in the layer between 0 and 10 cm. There was significant SOC accumulation (0-60 cm) in the NT soil (50.86 Mg/hm 2) compared with that in the CT soil (46.00 Mg/hm 2). The total CO 2 flux of soil respiration under NT was greater than that under CT. However, according to a carbon balance analysis, NT acted as a carbon sink compared to CT as a carbon source. This favored carbon sequestration in the farmland system. Therefore, long-term NT practice can increase soil carbon sequestration and reduce GHG emissions. The carbon emission coefficients are from literatures and N 2O emission is not considered in the study. These may affect the results, but the trend among the different tillage system remains unchanged. With the improvement of the parameters, the accuracy of the assessment can be further improved. NT can be a significant innovation for carbon-friendly agricultural production technology in Northern China, because of its savings of energy/labor/time, reduction of GHG emissions, and benefits of SOC sequestration.
  • Authors:
    • Zhang KeRong
    • Dang HaiShan
    • Zhang QuanFa
    • Cheng XiaoLi
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 7
  • Year: 2015
  • Summary: Knowledge of soil organic matter (SOM) dynamics following deforestation or reforestation is essential for evaluating carbon (C) budgets and cycle at regional or global scales. Worldwide land-use changes involving conversion of vegetation with different photosynthetic pathways (e.g. C 3 and C 4) offer a unique opportunity to quantify SOM decomposition rate and its response to climatic conditions using stable isotope techniques. We synthesized the results from 131 sites (including 87 deforestation observations and 44 reforestation observations) which were compiled from 36 published papers in the literatures as well as our observations in China's Qinling Mountains. Based on the 13C natural abundance analysis, we evaluated the dynamics of new and old C in top soil (0-20 cm) following land-use change and analyzed the relationships between soil organic C (SOC) decomposition rates and climatic factors. We found that SOC decomposition rates increased significantly with mean annual temperature and precipitation in the reforestation sites, and they were not related to any climatic factor in deforestation sites. The mean annual temperature explained 56% of variation in SOC decomposition rates by exponential model ( y=0.0014 e0.1395x ) in the reforestation sites. The proportion of new soil C increased following deforestation and reforestation, whereas the old soil C showed an opposite trend. The proportion of new soil C exceeded the proportion of old soil C after 45.4 years' reforestation and 43.4 years' deforestation, respectively. The rates of new soil C accumulation increased significantly with mean annual precipitation and temperature in the reforestation sites, yet only significantly increased with mean annual precipitation in the deforestation sites. Overall, our study provides evidence that SOC decomposition rates vary with temperature and precipitation, and thereby implies that global warming may accelerate SOM decomposition.
  • Authors:
    • Antille,D. L.
    • Chamen,W. C. T.
    • Tullberg,J. N.
    • Lal,R.
  • Source: Transactions of the ASABE
  • Volume: 58
  • Issue: 3
  • Year: 2015
  • Summary: The drive toward adoption of conservation agriculture to reduce costs and increase production sustainably causes concern due to the potentially negative effects of increased soil compaction. Soil compaction reduces aeration, water infiltration, and saturated hydraulic conductivity and increases the risk of waterlogging. Controlled traffic farming (CTF) is a system in which: (1) all machinery has the same or modular working and track width so that field traffic can be confined to the least possible area of permanent traffic lanes, (2) all machinery is capable of precise guidance along those permanent traffic lanes, and (3) the layout of the permanent traffic lanes is designed to optimize surface drainage and logistics. Without CTF, varying equipment operating and track widths translate into random traffic patterns, which can cover up to 85% of the cultivated field area each time a crop is produced. Nitrous oxide (N2O) is the greatest contributor to agriculture's greenhouse gas (GHG) emissions from cropping, and research suggests that its production increases significantly under conditions of high (>60%) water-filled porosity when nitrate (mainly from fertilizer N) and carbon (usually from crop residues) are available. Self-amelioration of soils affected by compaction occurs slowly from the surface downward; however, the rate of amelioration decreases with increase in depth. Consequently, all soils in non-CTF systems in mechanized agriculture are prone to some degree of compaction, which compromises water infiltration, increases the frequency and duration of waterlogged conditions, reduces gaseous exchange between soil and the atmosphere, inhibits root penetration and exploitation of nutrients and water in the subsoil, and enhances N2O emissions. Adoption of CTF increases soil porosity in the range of 5% to 70%, water infiltration by a factor of 4, and saturated hydraulic conductivity by a factor of 2. The greater cropping opportunity and enhanced crop growth for given fertilizer and rainfall inputs offered by CTF, coupled with no-tillage, provide potential for enhanced soil carbon sequestration. Reduced need and intensity of tillage, where compaction is avoided, also helps protect soil organic matter in stable aggregates, which may otherwise be exposed and oxidized. There is both circumstantial and direct evidence to suggest that improved soil structural conditions and aeration offered by CTF can reduce N2O emissions by 20% to 50% compared with non-CTF. It is not compaction per se that increases the risk of N2O emissions but rather the increased risk of waterlogging and increase in water-filled pore space. There may be an elevated risk of GHG emissions from the relatively small area of permanent traffic lanes (typically <20% of total cultivated area) if these are not managed appropriately. Quantification of the benefits of compaction avoidance in terms of GHG emissions may be possible through the use of well-developed models. © 2015 American Society of Agricultural and Biological Engineers.
  • Authors:
    • Frank,D.
    • Reichstein,M.
    • Bahn,M.
    • Thonicke,K.
    • Frank,D.
    • Mahecha,M. D.
    • Smith,P.
    • Velde,M. van der
    • Vicca,S.
    • Babst,F.
    • Beer,C.
    • Buchmann,N.
    • Canadell,J. G.
    • Ciais,P.
    • Cramer,W.
    • Ibrom,A.
    • Miglietta,F.
    • Poulter,B.
    • Rammig,A.
    • Seneviratne,S. I.
    • Walz,A.
    • Wattenbach,M.
    • Zavala,M. A.
    • Zscheischler,J.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 8
  • Year: 2015
  • Summary: Extreme droughts, heat waves, frosts, precipitation, wind storms and other climate extremes may impact the structure, composition and functioning of terrestrial ecosystems, and thus carbon cycling and its feedbacks to the climate system. Yet, the interconnected avenues through which climate extremes drive ecological and physiological processes and alter the carbon balance are poorly understood. Here, we review the literature on carbon cycle relevant responses of ecosystems to extreme climatic events. Given that impacts of climate extremes are considered disturbances, we assume the respective general disturbance-induced mechanisms and processes to also operate in an extreme context. The paucity of well-defined studies currently renders a quantitative meta-analysis impossible, but permits us to develop a deductive framework for identifying the main mechanisms (and coupling thereof) through which climate extremes may act on the carbon cycle. We find that ecosystem responses can exceed the duration of the climate impacts via lagged effects on the carbon cycle. The expected regional impacts of future climate extremes will depend on changes in the probability and severity of their occurrence, on the compound effects and timing of different climate extremes, and on the vulnerability of each land-cover type modulated by management. Although processes and sensitivities differ among biomes, based on expert opinion, we expect forests to exhibit the largest net effect of extremes due to their large carbon pools and fluxes, potentially large indirect and lagged impacts, and long recovery time to regain previous stocks. At the global scale, we presume that droughts have the strongest and most widespread effects on terrestrial carbon cycling. Comparing impacts of climate extremes identified via remote sensing vs. ground-based observational case studies reveals that many regions in the (sub-)tropics are understudied. Hence, regional investigations are needed to allow a global upscaling of the impacts of climate extremes on global carbon-climate feedbacks.
  • Authors:
    • Jacinthe,P. A.
    • Vidon,P.
    • Fisher,K.
    • Liu,X.
    • Baker,M. E.
  • Source: Journal of Environmental Quality
  • Volume: 44
  • Issue: 4
  • Year: 2015
  • Summary: Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO 2 and CH 4 fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly ( P22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH 4-C m -2 d -1), probably due to low soil temperature. Although CH 4 flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH 4 sources, with annual emission averaging +0.040.17 and +0.921.6 kg CH 4-C ha -1, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH 4 emission, underscoring the significance of landscape heterogeneity on CH 4 dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH 4 sink (-1.080.22 kg CH 4-C ha -1 yr -1), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH 4 sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.
  • Authors:
    • Jarvie,H. P.
    • Sharpley,A. N.
    • Flaten,D.
    • Kleinman,P. J. A.
    • Jenkins,A.
    • Simmons,T.
  • Source: Journal of Environmental Quality
  • Volume: 44
  • Issue: 4
  • Year: 2015
  • Summary: We make the case that phosphorus (P) is inextricably linked to an increasingly fragile, interconnected, and interdependent nexus of water, energy, and food security and should be managed accordingly. Although there are many other drivers that influence water, energy, and food security, P plays a unique and under-recognized role within the nexus. The P paradox derives from fundamental challenges in meeting water, energy, and food security for a growing global population. We face simultaneous dilemmas of overcoming scarcity of P to sustain terrestrial food and biofuel production and addressing overabundance of P entering aquatic systems, which impairs water quality and aquatic ecosystems and threatens water security. Historical success in redistributing rock phosphate as fertilizer to enable modern feed and food production systems is a grand societal achievement in overcoming inequality. However, using the United States as the main example, we demonstrate how successes in redistribution of P and reorganization of farming systems have broken local P cycles and have inadvertently created instability that threatens resilience within the nexus. Furthermore, recent expansion of the biofuels sector is placing further pressure on P distribution and availability. Despite these challenges, opportunities exist to intensify and expand food and biofuel production through recycling and better management of land and water resources. Ultimately, a strategic approach to sustainable P management can help address the P paradox, minimize tradeoffs, and catalyze synergies to improve resilience among components of the water, energy, and food security nexus.
  • Authors:
    • Jones,Andrew D.
    • Calvin,Katherine V.
    • Collins,William D.
    • Edmonds,James
  • Volume: 131
  • Issue: 4
  • Year: 2015
  • Summary: We demonstrate the effectiveness of a new method for quantifying radiative forcing from land use and land cover change (LULCC) within an integrated assessment model, the Global Change Assessment Model (GCAM). The method relies on geographically differentiated estimates of radiative forcing from albedo change associated with major land cover transitions derived from the Community Earth System Model. We find that conversion of 1 km(2) of woody vegetation (forest and shrublands) to non-woody vegetation (crops and grassland) yields between 0 and -0.71 nW/m(2) of globally averaged radiative forcing determined by the vegetation characteristics, snow dynamics, and atmospheric radiation environment characteristic within each of 151 regions we consider globally. Across a set of scenarios designed to span a range of potential future LULCC, we find LULCC forcing ranging from -0.06 to -0.29 W/m(2) by 2070 depending on assumptions regarding future crop yield growth and whether climate policy favors afforestation or bioenergy crops. Inclusion of this previously uncounted forcing in the policy targets driving future climate mitigation efforts leads to changes in fossil fuel emissions on the order of 1.5 PgC/yr by 2070 for a climate forcing limit of 4.5 Wm(-2), corresponding to a 12-67 % change in fossil fuel emissions depending on the scenario. Scenarios with significant afforestation must compensate for albedo-induced warming through additional emissions reductions, and scenarios with significant deforestation need not mitigate as aggressively due to albedo-induced cooling. In all scenarios considered, inclusion of albedo forcing in policy targets increases forest and shrub cover globally.