51. Possible impact of the Renewable Energy Directive on N fertilization intensity and yield of winter oilseed rape in different cropping systems

• Authors:
  • Boettcher, U.
  • Pahlmann, I.
  • Kage, H.
  • Sieling, K.
• Source: Biomass & Bioenergy
• Volume: 57
• Year: 2013
• Summary: In 2009, the Renewable Energy Directive (RED), established sustainability criteria for biofuels including legal thresholds for specific greenhouse gas (GHG) emissions, expressed as g CO(2)eq per MJ of biofuel. Because biofuels are a major market for winter oilseed rape (WOSR), investigating the possible impact of the RED on WOSR cropping practices is prudent. This study analyses GHG emissions for WOSR cropping practices (namely N fertilization intensity, tillage method and crop rotation) basing on a 6-year field trial in a high yielding area of northern Germany. Using the International Panel on Climate Change (IPCC) methodology the field emissions of nitrous oxide (N2O) are calculated from the nitrogen (N) inputs to the cropping system. Results showed that the predominant source of GHG emissions is the N related emissions from production of fertilizer and N2O field emissions. Specific GHG emissions are lowest without N fertilizer but rise continuously with increasing N rates. Yield per ha also responded to N fertilization resulting in lowered acreage productivity when reducing GHG emissions by reducing N fertilization level. Most calculated scenarios and cropping systems result in a drastic decrease of N fertilization to achieve thresholds, causing substantial yield losses. To a certain extent, the required drastic reduction of N fertilization in some scenarios is driven by using the IPCC methodology for calculating N2O emissions. Therefore characteristics of this methodology are also discussed within this study. To mitigate the impact of the RED on WOSR, peas (legumes) may be a possible preceding crop to WOSR. (C) 2013 Elsevier Ltd. All rights reserved.

52. 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

• Authors:
  • Suddick, E. C.
  • Six, J.
• Source: Science of the Total Environment
• Volume: 465
• Year: 2013
• Summary: 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 degrees 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.

53. Baseline-dependent responses of soil organic carbon dynamics to climate and land disturbances.

• Authors:
  • Liu, S. G.
  • Tan, Z. X.
• Source: Applied and Environmental Soil Science
• Volume: 2013
• Issue: 2013
• Year: 2013
• Summary: Terrestrial carbon (C) sequestration through optimizing land use and management is widely considered a realistic option to mitigate the global greenhouse effect. But how the responses of individual ecosystems to changes in land use and management are related to baseline soil organic C (SOC) levels still needs to be evaluated at various scales. In this study, we modeled SOC dynamics within both natural and managed ecosystems in North Dakota of the United States and found that the average SOC stock in the top 20 cm depth of soil lost at a rate of 450 kg C ha -1 yr -1 in cropland and 110 kg C ha -1 yr -1 in grassland between 1971 and 1998. Since 1998, the study area had become a SOC sink at a rate of 44 kg C ha -1 yr -1. The annual rate of SOC change in all types of lands substantially depends on the magnitude of initial SOC contents, but such dependency varies more with climatic variables within natural ecosystems and with management practices within managed ecosystems. Additionally, soils with high baseline SOC stocks tend to be C sources following any land surface disturbances, whereas soils having low baseline C contents likely become C sinks following conservation management.

54. Net CO2 exchange and carbon budgets of a three-year crop rotation following conversion of perennial lands to annual cropping in Manitoba, Canada

• Authors:
  • Fraser, T. J.
  • Amiro, B. D.
  • Taylor, A. M.
• Source: Agricultural and Forest Meteorology
• Volume: 182-183
• Year: 2013
• Summary: Eddy covariance flux towers were used to measure net ecosystem production over three adjacent agricultural fields in Manitoba, Canada, from 2009 to 2011. Two fields were converted from long-term perennial hay/pasture to annual cropping, while the third field served as a control field that was maintained as hay/pasture. One converted field had a rotation of oat-canola-oat crops, while the second was hay-oat-fallow. Weather was an important driver of inter-annual variability, with poor yields on all fields in 2011 because of dry conditions in summer, with the summer-fallow condition on one field caused by excess spring moisture not allowing planting. The cumulative net ecosystem production of the oat-canola-oat field showed a net CO2 emission of 100 g Cm-2, the hay-oat-fallow field emitted 500 g Cm-2, and the hay field gained 550 g C m(-2) by the end of the 30-month study period. The hay field had the highest cumulative gross primary production of 2500 g C m(-2), whereas the oat-canola-oat and hay-oat-fallow fields had only about 1400 g C m(-2). The perennial field had the advantage of both early- and late-season growth when crops were absent on the other fields. The hay and hay-oat-fallow fields had comparable cumulative ecosystem respiration (1400 g Cm-2). Manure additions contributed 300 g C m(-2) on the two converted fields. With harvest exports and manure additions included, the oat-canola-oat field was a carbon source of 240 g Cm-2, the hay-oat-fallow field was a source of 415 g C m(-2), and the hay/pasture field was a sink of 120 g C m(-2) over the 30-month period.

55. Modifying the Soil and Water Assessment Tool to simulate cropland carbon flux: Model development and initial evaluation

• Authors:
  • Srinivasan, R.
  • Williams, J. R.
  • Arnold, J. G.
  • Izaurralde, R. C.
  • Zhang, X.
• Source: Science of the Total Environment
• Volume: 463-464
• Year: 2013
• Summary: Climate change is one of the most compelling modern issues and has important implications for almost every aspect of natural and human systems. The Soil and Water Assessment Tool (SWAT) model has been applied worldwide to support sustainable land and water management in a changing climate. However, the inadequacies of the existing carbon algorithm in SWAT limit its application in assessing impacts of human activities on CO2 emission, one important source of greenhouse gasses (GHGs) that traps heat in the earth system and results in global warming. In this research, we incorporate a revised version of the CENTURY carbon model into SWAT to describe dynamics of soil organic matter (SOM)-residue and simulate land-atmosphere carbon exchange. We test this new SWAT-C model with daily eddy covariance (EC) observations of net ecosystem exchange (NEE) and evapotranspiration (ET) and annual crop yield at six sites across the U.S. Midwest. Results show that SWAT-C simulates well multi-year average NEE and ET across the spatially distributed sites and capture the majority of temporal variation of thesetwo variables at a daily time scale at each site. Our analyses also reveal that performance of SWAT-C is influenced by multiple factors, such as crop management practices (irrigated vs. rainfed), completeness and accuracy of input data, crop species, and initialization of state variables. Overall, the new SWAT-C demonstrates favorable performance for simulating land-atmosphere carbon exchange across agricultural sites with different soils, climate, and management practices. SWAT-C is expected to serve as a useful tool for including carbon flux into consideration in sustainable watershed management under a changing climate. We also note that extensive assessment of SWAT-C with field observations is required for further improving the model and understanding potential uncertainties of applying it across large regions with complex landscapes.

56. Farmer beliefs and concerns about climate change and attitudes toward adaptation and mitigation: Evidence from Iowa

• Authors:
  • Arbuckle,J. Gordon, Jr.
  • Morton,Lois Wright
  • Hobbs,Jon
• Source: Climatic Change
• Volume: 118
• Issue: 3-4
• Year: 2013
• Summary: Agriculture is both vulnerable to climate change impacts and a significant source of greenhouse gases. Increasing agriculture's resilience and reducing its contribution to climate change are societal priorities. Survey data collected from Iowa farmers are analyzed to answer the related research questions: (1) do farmers support adaptation and mitigation actions, and (2) do beliefs and concerns about climate change influence those attitudes. Results indicate that farmers who were concerned about the impacts of climate change on agriculture and attributed it to human activities had more positive attitudes toward both adaptive and mitigative management strategies. Farmers who believed that climate change is not a problem because human ingenuity will enable adaptations and who did not believe climate change is occurring or believed it is a natural phenomenon-a substantial percentage of farmers-tended not to support mitigation.

57. Nitrogen fixation and transfer in grass-clover leys under organic and conventional cropping systems

• Authors:
  • Oberson,A.
  • Frossard,E.
  • Buehlmann,C.
  • Mayer,J.
  • Maeder,P.
  • Luescher,A.
• Source: Plant and Soil
• Volume: 371
• Issue: 1-2
• Year: 2013
• Summary: Symbiotic dinitrogen (N-2) fixation is the most important external N source in organic systems. Our objective was to compare symbiotic N-2 fixation of clover grown in organically and conventionally cropped grass-clover leys, while taking into account nutrient supply gradients. We studied leys of a 30-year-old field experiment over 2 years in order to compare organic and conventional systems at two fertilization levels. Using N-15 natural abundance methods, we determined the proportion of N derived from the atmosphere (PNdfa), the amount of Ndfa (ANdfa), and the transfer of clover N to grasses for both red clover (Trifolium pratense L.) and white clover (Trifolium repens L.). In all treatments and both years, PNdfa was high (83 to 91 %), indicating that the N-2 fixation process is not constrained, even not in the strongly nutrient deficient non-fertilized control treatment. Annual ANdfa in harvested clover biomass ranged from 6 to 16 g N m(-2). At typical fertilizer input levels, lower sward yield in organic than those in conventional treatments had no effect on ANdfa because of organic treatments had greater clover proportions. In two-year-old leys, on average, 51 % of N taken up by grasses was transferred from clover. Both, organically and conventionally cropped grass-clover leys profited from symbiotic N-2 fixation, with high PNdfa, and important transfer of clover N to grasses, provided sufficient potassium- and phosphorus-availability to sustain clover biomass production.

58. Climate change impacts on dryland cropping systems in the Central Great Plains, USA.

• Authors:
  • Ahuja, L. R.
  • Saseendran, S. A.
  • Green, T. R.
  • Ma, L. W.
  • Nielsen, D. C.
  • Walthall, C. L.
  • Ko, J. H.
• Source: Climatic Change
• Volume: 111
• Issue: 2
• Year: 2012
• Summary: Agricultural systems models are essential tools to assess potential climate change (CC) impacts on crop production and help guide policy decisions. In this study, impacts of projected CC on dryland crop rotations of wheat-fallow (WF), wheat-corn-fallow (WCF), and wheat-corn-millet (WCM) in the U.S. Central Great Plains (Akron, Colorado) were simulated using the CERES V4.0 crop modules in RZWQM2. The CC scenarios for CO 2, temperature and precipitation were based on a synthesis of Intergovernmental Panel on Climate Change (IPCC 2007) projections for Colorado. The CC for years 2025, 2050, 2075, and 2100 (CC projection years) were super-imposed on measured baseline climate data for 15-17 years collected during the long-term WF and WCF (1992-2008), and WCM (1994-2008) experiments at the location to provide inter-annual variability. For all the CC projection years, a decline in simulated wheat yield and an increase in actual transpiration were observed, but compared to the baseline these changes were not significant ( p>0.05) in all cases but one. However, corn and proso millet yields in all rotations and projection years declined significantly ( p<0.05), which resulted in decreased transpiration. Overall, the projected negative effects of rising temperatures on crop production dominated over any positive impacts of atmospheric CO 2 increases in these dryland cropping systems. Simulated adaptation via changes in planting dates did not mitigate the yield losses of the crops significantly. However, the no-tillage maintained higher wheat yields than the conventional tillage in the WF rotation to year 2075. Possible effects of historical CO 2 increases during the past century (from 300 to 380 ppm) on crop yields were also simulated using 96 years of measured climate data (1912-2008) at the location. On average the CO 2 increase enhanced wheat yields by about 30%, and millet yields by about 17%, with no significant changes in corn yields.

59. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan.

• Authors:
  • Lemke, R. L.
  • Vandenbygaart, A. J.
  • Campbell, C. A.
  • Lafond, G. P.
  • McConkey, B. G.
  • Grant, B.
• Source: Canadian Journal of Soil Science
• Volume: 92
• Issue: 3
• Year: 2012
• Summary: Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958-2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat ( Triticum aestivum L.) (F-W), or F-W-W receiving minimum fertilizer for the previous 50 yr. We sampled soil in 1987, 1996 (6 yr after changing from conventional tillage to no-tillage management and increasing N rates markedly) and again in 2007. The SOC (0-15 cm depth) in unfertilized F-W and F-W-W appears not to have changed from the assumed starting level, even after 20 yr of no-till, but SOC in unfertilized continuous wheat (Cont W) increased slightly [not significant ( P>0.05)] in 30 yr, but increased more after 20 yr of no-till (but still not significant). No-till plus proper fertilization for 20 yr increased the SOC of F-W, F-W-W and Cont W in direct proportion to cropping frequency. The SOC in the LGM-W-W (unfertilized) system was higher than unfertilized F-W-W in 1987, but 20 yr of no-tillage had no effect, likely because grain yields and C inputs were depressed by inadequate available P. Soil organic carbon in the two aggrading systems [Cont W (N+P) and F-W-W-hay(H)-H-H (unfertilized)] increased significantly ( P<0.05) in the first 30 yr; however, a further 20 yr of no-tillage (and increased N in the case of the Cont W) did not increase SOC suggesting that the SOC had reached a steady-state for this soil and management system. The Campbell model effectively simulated SOC changes except for Cont W(N+P), which it overestimated because the model is ineffective in simulating SOC in very fertile systems. After 50 yr, efficiency of conversion of residue C inputs to SOC was negligible for unfertilized F-W and F-W-W, was 3 to 4% for fertilized fallow-containing systems, was about 6 or 7% for Cont W, and about 11% for the unfertilized F-W-W-H-H-H systems.

60. Integrated crops and livestock in central North Dakota, USA: agroecosystem management to buffer soil change.

• Authors:
  • Karn, J. F.
  • Liebig, M. A.
  • Tanaka, D. L.
  • Kronberg, S. L.
  • Scholljegerdes, E. J.
• Source: Renewable Agriculture and Food Systems
• Volume: 27
• Issue: 2
• Year: 2012
• Summary: Integrated crop-livestock systems have been purported to have numerous agronomic and environmental benefits, yet information documenting their long-term impact on the soil resource is lacking. This study sought to quantify the effects of an integrated crop-livestock system on near-surface soil properties in central North Dakota, USA. Soil bulk density, electrical conductivity, soil pH, extractable N and P, potentially mineralizable N, soil organic carbon (SOC) and total nitrogen (TN) were measured 3, 6 and 9 years after treatment establishment to evaluate the effects of residue management (Grazed, Hayed and Control), the frequency of hoof traffic (High traffic, Low traffic and No traffic), season (Fall and Spring) and production system (integrated annual cropping versus perennial grass) on near-surface soil quality. Values for soil properties were incorporated into a soil quality index (SQI) using the Soil Management Assessment Framework to assess overall treatment effects on soil condition. Residue management and frequency of hoof traffic did not affect near-surface soil properties throughout the evaluation period. Aggregated SQI values did not differ between production systems 9 years after treatment establishment (integrated annual cropping=0.91, perennial grass=0.93; P=0.57), implying a near-identical capacity of each system to perform critical soil functions. Results from the study suggest that with careful management, agricultural producers can convert perennial grass pastures to winter-grazed annual cropping systems without adversely affecting near-surface soil quality. However, caution should be exercised in applying results to other regions or management systems. The consistent freeze/thaw and wet/dry cycles typical of the northern Great Plains, coupled with the use of no-till management, modest fertilizer application rates and winter grazing likely played an important role in the outcome of the results.