• Authors:
    • Quenea, K.
    • Mutema, M.
    • Muller-Nedebock, D.
    • Mchunu, C.
    • Everson, C.
    • Dlamini, P.
    • Darboux, F.
    • Bourennane, H.
    • Alexis, M.
    • Abdalla, K.
    • Chaplot, V.
    • Thenga, H.
    • Chivenge, P.
  • Source: Journal
  • Volume: 203
  • Issue: 1
  • Year: 2015
  • Summary: The impact of agricultural practices on CO 2 emissions from soils needs to be understood and quantified to enhance ecosystem functions, especially the ability of soils to sequester atmospheric carbon (C), while enhancing food and biomass production. The objective of this study was to assess CO 2 emissions in the soil surface following tillage abandonment and to investigate some of the underlying soil physical, chemical and biological controls. Maize ( Zea mays) was planted under conventional tillage (T) and no-tillage (NT), both without crop residues under smallholder farming conditions in Potshini, South Africa. Intact top-soil (0-0.05 m) core samples (N=54) from three 5*15 m 2 plots per treatment were collected two years after conversion of T to NT to evaluate the short-term CO 2 emissions. Depending on the treatment, cores were left intact, compacted by 5 and 10%, or had surface crusts removed. They were incubated for 20 days with measurements of CO 2 fluxes twice a day during the first three days and once a day thereafter. Soil organic C (SOC) content, soil bulk density (rho b), aggregate stability, soil organic matter quality, and microbial biomass and its activity were evaluated at the onset of the incubation. CO 2 emissions were 22% lower under NT compared with T with CO 2 emissions of 0.90.10 vs 1.10.10 mg C-CO 2 gC -1 day -1 under NT and T, respectively, suggesting greater SOC protection under NT. However, there were greater total CO 2 emissions per unit of surface by 9% under NT compared to T (1.150.03 vs 1.050.04 g C-CO 2 m -2 day -1). SOC protection significantly increased with the increase in soil bulk density ( r=0.89) and aggregate stability (from 1.70.25 mm to 2.30.31, r=0.50), and to the decrease in microbial biomass and its activity ( r=-0.59 and -0.57, respectively). In contrast, the greater NT CO 2 emissions per m 2 were explained by top-soil enrichment in SOC by 48% (from 12.40.2 to 19.10.4 g kg -1, r=0.59). These results on the soil controls of tillage impact on CO 2 emissions are expected to inform on the required shifts in agricultural practices for enhancing C sequestration in soils. In the context of the study, any mechanism favoring aggregate stability and promoting SOC allocation deep in the soil profile rather than in the top-soil would greatly diminish soil CO 2 outputs and thus stimulate C sequestration.
  • Authors:
    • Dondini,M.
    • Jones,E. O.
    • Richards,M.
    • Pogson,M.
    • Rowe,R. L.
    • Keith,A. M.
    • Perks,M. P.
    • McNamara,N. P.
    • Smith,J. U.
    • Smith,P.
  • Source: Global Change Biology
  • Volume: 7
  • Issue: 3
  • Year: 2015
  • Summary: Understanding and predicting the effects of land-use change to short rotation forestry (SRF) on soil carbon (C) is an important requirement for fully assessing the C mitigation potential of SRF as a bioenergy crop. There is little current knowledge of SRF in the UK and in particular a lack of consistent measured data sets on the direct impacts of land use change on soil C stocks. The ECOSSE model was developed to simulate soil C dynamics and greenhouse gas (GHG) emissions in mineral and organic soils. The ECOSSE model has already been applied spatially to simulate land-use change impacts on soil C and GHG emissions. However, it has not been extensively evaluated under SRF. Eleven sites comprising 29 transitions in Britain, representing land-use change from nonwoodland land uses to SRF, were selected to evaluate the performance of ECOSSE in predicting soil C and soil C change in SRF plantations. The modelled C under SRF showed a strong correlation with the soil C measurements at both 0-30 cm ( R=0.93) and 0-100 cm soil depth ( R=0.82). As for the SRF plots, the soil C at the reference sites have been accurately simulated by the model. The extremely high correlation for the reference fields ( R ≥0.99) shows a good performance of the model spin-up. The statistical analysis of the model performance to simulate soil C and soil C changes after land-use change to SRF highlighted the absence of significant error between modelled and measured values as well as the absence of significant bias in the model. Overall, this evaluation reinforces previous studies on the ability of ECOSSE to simulate soil C and emphasize its accuracy to simulate soil C under SRF plantations.
  • Authors:
    • Aziz, S. A.
    • Gong, P.
    • Hansen, M.
    • Justice, C.
    • Becker-Reshef, I.
    • Herrero, M.
    • Wood-Sichra, U.
    • Thornton, P.
    • Mosnier, A.
    • Havlik, P.
    • Perger, C.
    • Schill, C.
    • Albrecht, F.
    • Duerauer, M.
    • Moltchanova, E.
    • Bun, A.
    • You, L.
    • McCallum, I.
    • See, L.
    • Fritz, S.
    • Cipriani, A.
    • Cumani, R.
    • Cecchi, G.
    • Conchedda, G.
    • Ferreira, S.
    • Gomez, A.
  • Source: Journal Article
  • Volume: 21
  • Issue: 5
  • Year: 2015
  • Summary: A new 1 km global IIASA-IFPRI cropland percentage map for the baseline year 2005 has been developed which integrates a number of individual cropland maps at global to regional to national scales. The individual map products include existing global land cover maps such as GlobCover 2005 and MODIS v.5, regional maps such as AFRICOVER and national maps from mapping agencies and other organizations. The different products are ranked at the national level using crowdsourced data from Geo-Wiki to create a map that reflects the likelihood of cropland. Calibration with national and subnational crop statistics was then undertaken to distribute the cropland within each country and subnational unit. The new IIASA-IFPRI cropland product has been validated using very high-resolution satellite imagery via Geo-Wiki and has an overall accuracy of 82.4%. It has also been compared with the EarthStat cropland product and shows a lower root mean square error on an independent data set collected from Geo-Wiki. The first ever global field size map was produced at the same resolution as the IIASA-IFPRI cropland map based on interpolation of field size data collected via a Geo-Wiki crowdsourcing campaign. A validation exercise of the global field size map revealed satisfactory agreement with control data, particularly given the relatively modest size of the field size data set used to create the map. Both are critical inputs to global agricultural monitoring in the frame of GEOGLAM and will serve the global land modelling and integrated assessment community, in particular for improving land use models that require baseline cropland information. These products are freely available for downloading from the http://cropland.geo-wiki.org website.
  • Authors:
    • Pethybridge, S. J.
    • Hay, F.
  • Source: Web Of Knowledge
  • Issue: 1073
  • Year: 2015
  • Summary: A desktop study was undertaken to assess the contribution of the pyrethrum industry in Tasmania, Australia to on-farm greenhouse gas (GHG) emissions in comparison to potato and onion. Pyrethrum used significantly less diesel in transport than potato or onion. This was mainly due to the lower weight of dried flowers harvested from pyrethrum crops in comparison to the weight of crop from potato and onion fields (60 t/ha). First harvest pyrethrum required a similar amount of diesel to potato and onion for tractor and harvester operations. However, older pyrethrum crops required only 41% of the diesel used in potato and onion crops due mainly to the perennial nature of pyrethrum and the absence of cultivation in years subsequent to planting. Pyrethrum required greater inputs (kg a.i./ha) of herbicides and lower inputs of fungicides than potato and onion. All three crops required little input of insecticides. Pyrethrum had substantially lower inputs of nitrogen (N) and phosphorus (P) than potato or onion. First-harvest pyrethrum required only 38 and 59% of the N required by potato and onion, respectively. Moreover, pyrethrum required lower potassium (K) than potato, but higher K than onion. The electricity consumption associated with irrigation of pyrethrum and onion were similar, and amounted to 39% that of potato, due to the higher irrigation requirement of potato (5.1 ML/ha) in comparison to pyrethrum and onion (2.0 ML/ha) in Tasmania. The global warming potential (GWP) per hectare associated with planting to harvest of first year pyrethrum (18 months) and subsequently from one harvest to another (12 months) was estimated at 4,128.8 and 2,184.7 kg CO 2-e/ha, respectively. By comparison the GWP resulting from planting to harvest of potato and onion in Tasmania (4 months) was estimated at 5,284.0 and 4,875.3 kg CO 2-e/ha. The GWP of first year pyrethrum was therefore 78% that of potato and 85% that of onion, while the annual GWP per hectare of older pyrethrum fields was 41% that of potato and 45% that of onion. This study was based on strict assumptions and on generic emission factors for greenhouse gases. Therefore caution is required with the absolute figure for GWP. However, this study indicated that the on-farm production of pyrethrum is a relatively low contributor to GHG production on a per hectare basis, in comparison to other annual crops often grown in rotation.
  • Authors:
    • Van Dael, M.
    • Witters, N.
    • Njakou Djomo, S.
    • Gabrielle, B.
    • Ceulemans, R.
  • Source: Article
  • Volume: 154
  • Year: 2015
  • Summary: Bioenergy (i.e., bioheat and bioelectricity) could simultaneously address energy insecurity and climate change. However, bioenergy's impact on climate change remains incomplete when land use changes (LUC), soil organic carbon (SOC) changes, and the auxiliary energy consumption are not accounted for in the life cycle. Using data collected from Belgian farmers, combined heat and power (CHP) operators, and a life cycle approach, we compared 40 bioenergy pathways to a fossil-fuel CHP system. Bioenergy required between 0.024 and 0.204MJ (0.86MJth+0.14 MJel)-1, and the estimated energy ratio (energy output-to-input ratio) ranged from 5 to 42. SOC loss increased the greenhouse gas (GHG) emissions of residue based bioenergy. On average, the iLUC represented ~67% of the total GHG emissions of bioenergy from perennial energy crops. However, the net LUC (i.e., dLUC+iLUC) effects substantially reduced the GHG emissions incurred during all phases of bioenergy production from perennial crops, turning most pathways based on energy crops to GHG sinks. Relative to fossil-fuel based CHP all bioenergy pathways reduced GHG emissions by 8-114%. Fluidized bed technologies maximize the energy and the GHG benefits of all pathways. The size and the power-to-heat ratio for a given CHP influenced the energy and GHG performance of these bioenergy pathways. Even with the inclusion of LUC, perennial crops had better GHG performance than agricultural and forest residues. Perennial crops have a high potential in the multidimensional approach to increase energy security and to mitigate climate change. The full impacts of bioenergy from these perennial energy crops must, however, be assessed before they can be deployed on a large scale. © 2015 The Authors.
  • Authors:
    • Dufour, J.
    • I., Diego
    • Peters, J. F.
  • Source: Science Article
  • Volume: 49
  • Issue: 8
  • Year: 2015
  • Summary: The application of biochar as a soil amendment is a potential strategy for carbon sequestration. In this paper, a slow pyrolysis system for generating heat and biochar from lignocellulosic energy crops is simulated and its life-cycle performance compared with that of direct biomass combustion. The use of the char as biochar is also contrasted with alternative use option's: cofiring in coal power plants, use as charcoal, and use as a fuel for heat generation. Additionally, the influence on the results of the longterm stability of the biochar in the soil, as well as of biochar effects on biomass yield, is evaluated. Negative greenhouse gas emissions are obtained for the biochar system, indicating a significant carbon abatement potential. However, this is achieved at the expense of lower energy efficiency and higher impacts in the other assessed categories when compared to direct biomass combustion. When comparing the different use options of the pyrolysis char, the most favorable result is obtained for char cofiring substituting fossil coal, even assuming high long-term stability of the char. Nevertheless, a high sensitivity to biomass yield increase is found for biochar systems, In this sense, biochar application to low-quality soils where high yield increases are expected would show a more favorable performance in terms of global warming.
  • Authors:
    • Rey,A.
  • Source: Article
  • Volume: 21
  • Issue: 5
  • Year: 2015
  • Summary: Widespread recognition of the importance of soil CO 2 efflux as a major source of CO 2 to the atmosphere has led to active research. A large soil respiration database and recent reviews have compiled data, methods, and current challenges. This study highlights some deficiencies for a proper understanding of soil CO 2 efflux focusing on processes of soil CO 2 production and transport that have not received enough attention in the current soil respiration literature. It has mostly been assumed that soil CO 2 efflux is the result of biological processes (i.e. soil respiration), but recent studies demonstrate that pedochemical and geological processes, such as geothermal and volcanic CO 2 degassing, are potentially important in some areas. Besides the microbial decomposition of litter, solar radiation is responsible for photodegradation or photochemical degradation of litter. Diffusion is considered to be the main mechanism of CO 2 transport in the soil, but changes in atmospheric pressure and thermal convection may also be important mechanisms driving soil CO 2 efflux greater than diffusion under certain conditions. Lateral fluxes of carbon as dissolved organic and inorganic carbon occur and may cause an underestimation of soil CO 2 efflux. Traditionally soil CO 2 efflux has been measured with accumulation chambers assuming that the main transport mechanism is diffusion. New techniques are available such as improved automated chambers, CO 2 concentration profiles and isotopic techniques that may help to elucidate the sources of carbon from soils. We need to develop specific and standardized methods for different CO 2 sources to quantify this flux on a global scale. Biogeochemical models should include biological and non-biological CO 2 production processes before we can predict the response of soil CO 2 efflux to climate change. Improving our understanding of the processes involved in soil CO 2 efflux should be a research priority given the importance of this flux in the global carbon budget.
  • Authors:
    • Savabi, M. R.
    • Abdo, Z.
    • Sullivan, D. G.
    • Hubbard, R. K.
    • Scully, B. T.
    • Strickland, T. C.
    • Lee, R. D.
    • Olson, D. M.
    • Hawkins, G. L.
  • Source: Soil and Water Journal
  • Volume: 70
  • Issue: 3
  • Year: 2015
  • Summary: Although conservation tillage is widely believed to be an agricultural management practice effective for increasing soil carbon (C) accretion and associated soil quality, there is limited research to determine whether conservation tillage increases net C accretion versus simply altering the distribution of C content by soil depth. We implemented conservation farming practices (winter cover cropping plus strip tillage) for a nonirrigated corn (Zea mays L.) production system in the southeastern coastal plain of Georgia, United States, that had been previously managed under a conventional plow and harrow tillage regime. Total soil C and nitrogen (N) were measured on samples collected from 0 to 65 cm (0 to 25.6 in) at 57 sites before and after five years under conservation farming practices. Crop yield, winter and summer aboveground crop biomass production, and biomass C and N content were also measured annually at each site. Soil C increased an average of 20 Mg ha-1 (8.9 tn ac-1; 6 to 62 Mg C ha-1 [2.6 to 27.6 tn C ac-1], depending upon slope position) and was associated with a N increase of 2 Mg ha-1 (0.89 tn ac-1). Although 72% to 80% of the C accretion was in the top 35 cm (13.8 in), 3 to 6 Mg C ha-1 (1.3 to 2.6 tn C ac-1) was accreted from 35 to 65 cm (13.8 to 25.6 in). The soil C accreted during the study amounted to 36% of the net biomass C produced. Corn yield increased 2,200 kg ha-1 (1,964 lb ac-1) depending upon slope position (1,200 to 2,500 kg ha-1 [1,071 to 2,232 lb ac-1]) during the same time. Analysis indicated that soil C content from 15 to 35 cm (5.9 to 13.8 in) was the soil parameter primarily associated with corn yield. Season rainfall from planting to corn silking stage for both corn production years was the lowest in the past 45 years (20 to 25 cm [7.8 to 9.8 in] below the net crop demand) suggesting that soil C-mediated increase in plant-available soil water was a mechanism contributing to improved corn yield. Calculated estimates (from soil clay, sand, and C content) of increased soil water holding capacity suggest that C accretion in the top 35 cm (13.8 in) of soil potentially increased water storage enough to supply up to four days' worth of additional crop water demand. These results indicated that conservation farming practices can increase soil C and N accretion in degraded sandy soils of the humid southeastern United States coastal plain, and that increased soil C may potentially mitigate the deleterious effects of short-term rainfall deficits in nonirrigated production systems.
  • Authors:
    • Huang, S.
    • Pan, X.
    • Shi, Q.
    • Zeng, Y.
    • Sun, Y.
  • Source: Article
  • Volume: 153
  • Year: 2015
  • Summary: Runoff from farmland is of great importance to both agricultural and environmental sustainability. In the present study, a meta-analysis was conducted to quantify the effectiveness of no-tillage (NT) in reducing surface runoff and to explore the factors controlling the effectiveness. Results showed that overall, NT significantly reduced runoff by 21.9% and 27.2% compared to reduced tillage (RT) and conventional moldboard plow (MP), respectively. The effectiveness of NT in reducing runoff was higher under simulated than natural rainfall, particularly as compared to MP. The reduction in runoff under NT was significant and greatest for moderate slope gradients (5-10%) relative to both RT and MP, but without statistical significance for both gentle (10%) slope gradients. As compared to MP, the effectiveness of NT in reducing runoff decreased over time, whereas no such trend was found relative to RT. Compared to RT, NT significantly reduced runoff in soils with low clay content (<33% clay), while resulting in a slight but non-significant increase in runoff in soils with high clay content (=33% clay). The effectiveness of NT in reducing runoff compared to RT did not vary with tillage direction. Runoff was significantly reduced by NT with crop residue retention relative to RT, but not with residue removal. Our results conclude that NT needs to be adapted to specific environmental conditions and management practices for improved controls on runoff. © 2015.
  • Authors:
    • Lobell, D.
    • Abelleyra, D.
    • Veron, S.
  • Source: Article
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: Understanding regional impacts of recent climate trends can help anticipate how further climate change will affect agricultural productivity. We here used panel models to estimate the contribution of growing season precipitation (P), average temperature (T) and diurnal temperature range (DTR) on wheat, maize and soy yield and yield trends between 1971 and 2012 from 33 counties of the Argentine Pampas. A parallel analysis was conducted on a per county basis by adjusting a linear model to the first difference (i.e., subtracting from each value the previous year value) in yield and first difference in weather variables to estimate crop sensitivity to interannual changes in P, T, and DTR. Our results show a relatively small but significant negative impact of climate trends on yield which is consistent with the estimated crop and county specific sensitivity of yield to interannual changes in P, T and DTR and their temporal trends. Median yield loss from climate trends for the 1971-2012 period amounted to 5.4 % of average yields for maize, 5.1 % for wheat, and 2.6 % for soy. Crop yield gains for this time period could have been 15-20 % higher if climate remained without directional changes in the Pampas. On average, crop yield responded more to trends in T and DTR than in P. Translated into economic terms the observed reductions in maize, wheat, and soy yields due to climate trends in the Pampas would equal $1.1 B using 2013 producer prices. These results add to the increasing evidence that climate trends are slowing yield increase.