• Authors:
    • van Groenigen, K. J.
    • van Kessel, C.
    • Oenema, O.
    • Velthof, G. L.
    • van Groenigen, J. W.
  • Source: European Journal of Soil Science
  • Volume: 61
  • Issue: 6
  • Year: 2010
  • Summary: Agricultural soils are the main anthropogenic source of nitrous oxide (N2O), largely because of nitrogen (N) fertilizer use. Commonly, N2O emissions are expressed as a function of N application rate. This suggests that smaller fertilizer applications always lead to smaller N2O emissions. Here we argue that, because of global demand for agricultural products, agronomic conditions should be included when assessing N2O emissions. Expressing N2O emissions in relation to crop productivity (expressed as above-ground N uptake: "yield-scaled N2O emissions") can express the N2O efficiency of a cropping system. We show how conventional relationships between N application rate, N uptake and N2O emissions can result in minimal yield-scaled N2O emissions at intermediate fertilizer-N rates. Key findings of a meta-analysis on yield-scaled N2O emissions by non-leguminous annual crops (19 independent studies and 147 data points) revealed that yield-scaled N2O emissions were smallest (8.4 g N2O-N kg-1N uptake) at application rates of approximately 180-190 kg Nha-1 and increased sharply after that (26.8 g N2O-N kg-1 N uptake at 301 kg N ha-1). If the above-ground N surplus was equal to or smaller than zero, yield-scaled N2O emissions remained stable and relatively small. At an N surplus of 90 kg N ha-1 yield-scaled emissions increased threefold. Furthermore, a negative relation between N use efficiency and yield-scaled N2O emissions was found. Therefore, we argue that agricultural management practices to reduce N2O emissions should focus on optimizing fertilizer-N use efficiency under median rates of N input, rather than on minimizing N application rates.
  • Authors:
    • Liski, J.
    • Kitunen, V.
    • Spetz, P.
    • Tuomi, M.
    • Sonninen, E.
    • Oinonen, M.
    • Jungner, H.
    • Vanhala, P.
    • Hämäläinen, K.
    • Fritze, H.
    • Karhu, K.
  • Source: Ecology
  • Volume: 91
  • Issue: 2
  • Year: 2010
  • Summary: Feedback to climate warming from the carbon balance of terrestrial ecosystems depends critically on the temperature sensitivity of soil organic carbon (SOC) decomposition. Still, the temperature sensitivity is not known for the majority of the SOC, which is tens or hundreds of years old. This old fraction is paradoxically concluded to be more, less, or equally sensitive compared to the younger fraction. Here, we present results that explain these inconsistencies. We show that the temperature sensitivity of decomposition increases remarkably from the youngest annually cycling fraction (Q10 , 2) to a decadally cycling one (Q10 ¼ 4.2–6.9) but decreases again to a centennially cycling fraction (Q10 ¼ 2.4–2.8) in boreal forest soil. Compared to the method used for current global estimates (temperature sensitivity of all SOC equal to that of the total heterotrophic soil respiration), the soils studied will lose 30–45% more carbon in response to climate warming during the next few decades, if there is no change in carbon input. Carbon input, derivative of plant productivity, would have to increase by 100–120%, as compared to the earlier estimated 70–80%, in order to compensate for the accelerated decomposition.
  • Authors:
    • Kaufman, L.
  • Source: The New York Times
  • Year: 2010
  • Authors:
    • Loynachan, T. E.
    • Schultz, R. C.
    • Parkin, T. B.
    • Isenhart, T. M.
    • Kim, D. G.
  • Source: Journal of Environmental Quality
  • Volume: 39
  • Issue: 1
  • Year: 2010
  • Summary: While water quality functions of conservation buffers established adjacent to cropped Fields have been widely documented, the relative contribution of these re-established perennial plant systems to greenhouse gases has not been completely documented. In the case of methane (CH4), these systems have the potential to serve as sinks of CH4 or may provide favorable conditions for CH4 production. This study quantifies CH4 flux from soils of riparian buffer systems comprised of three vegetation types and compares these fluxes with those of adjacent crop fields. We measured soil properties and diel and seasonal variations of CH4 flux in 7 to 17 yr-old re-established riparian forest buffers, warm-season and cool-season grass filters, and an adjacent crop field located in the Bear Creek watershed in central Iowa. Forest buffer and grass filter soils had significantly lower bulk density (P < 0.01); and higher pH (P < 0.01), total carbon (TC) (P < 0.01), and total nitrogen (TN) (P < 0.01) than crop field soils. There was no significant relationship between CH4 flux mid soil moisture or soil temperature among sites within the range of conditions observed. Cumulative CH4 flux was -0.80 kg CH4-C ha(-1) yr(-1) in the cropped field, -0.416 kg CH4-C ha(-1) yr(-1) within the forest buffers, and 0.04 kg CH4-C ha(-1) yr(-1) within grass filters, but difference among vegetation covers was not significant. Results Suggest that CH4 flux was not changed after establishment of perennial vegetation on cropped soils, despite significant changes in soil properties.
  • Authors:
    • Kutcher, H. R.
    • Kryzanowski, L. M.
  • Source: Recent Trends in Soil Science and Agronomy Research in the Northern Great Plains of North America
  • Year: 2010
  • Summary: Variability in soil and crop productivity in the Northern Great Plains is related to the pedogenic development of the parent glacial deposits, climate, native vegetation, and topography. Anthropogenic field management over the past 100 years has contributed to additional field variability through tillage erosion, crop-fallow rotations, fertilizer management, livestock manure management and crop residue management. Field topography influences microclimate and the hydrological conditions within a landscape by the redistribution of water and soil thermal dynamics. Water movement from upper to lower slope and depression areas either by runoff or through subsoil will result in the physical redistribution of surface soil (erosion), translocation of soluble nutrients or accumulation of salts. The end result of this redistribution is drier warmer upper slopes, and wetter cooler lower slopes and depressions. This influences soil biological, chemical and physical processes that impact crop growth. Often, the lowest crop yields are measured on the upper slopes and the highest yields on the lower slopes. Upper slopes are prone to erosion, shallow surface horizons, higher carbonate levels, lower organic matter levels and lower available water. The lower slopes have deposits of eroded surface material, deeper surface horizons, greater depth to carbonates, higher organic matter levels and higher available water. However, spatial relationships between productivity and landscape position are not always consistent. Higher productivity does not always occur in lower slopes because yield reductions can occur as a result of planting delays, poor crop germination, poor soil aeration, poor drainage, poor root development, foliar and root diseases, compaction, nutrient deficiencies, weed competition, limited root development, stunted crop development, acidic soil and salinity. Precision farming provides an opportunity to utilize technology to manage the topographical and spatial variability. Elevation and positioning data collected from global positioning systems can be managed by means of geographic information systems. Landform segmentation provides a fundamental basis for subdividing fields into landscape management units based on topography. Field sensors such as crop yield monitors along with remote sensing, aerial photography, soil sampling and weed populations provide additional data layers needed for site specific management. Variable rate controllers provide the technology for fertilizer, manure, lime and herbicide applications. Ultimately, economics will determine the adoption of precision farming technology and practices.
  • Authors:
    • Paré, D.
    • Angers, D. A.
    • Laganière, J.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 1
  • Year: 2010
  • Summary: Deforestation usually results in significant losses of soil organic carbon (SOC). The rate and factors determining the recovery of this C pool with afforestation are still poorly understood. This paper provides a review of the influence of afforestation on SOC stocks based on a meta-analysis of 33 recent publications (totaling 120 sites and 189 observations), with the aim of determining the factors responsible for the restoration of SOC following afforestation. Based on a mixed linear model, the meta-analysis indicates that the main factors that contribute to restoring SOC stocks after afforestation are: previous land use, tree species planted, soil clay content, preplanting disturbance and, to a lesser extent, climatic zone. Specifically, this meta-analysis (1) indicates that the positive impact of afforestation on SOC stocks is more pronounced in cropland soils than in pastures or natural grasslands; (2) suggests that broadleaf tree species have a greater capacity to accumulate SOC than coniferous species; (3) underscores that afforestation using pine species does not result in a net loss of the whole soil-profile carbon stocks compared with initial values (agricultural soil) when the surface organic layer is included in the accounting; (4) demonstrates that clay-rich soils (>33%) have a greater capacity to accumulate SOC than soils with a lower clay content (<33%); (5) indicates that minimizing preplanting disturbances may increase the rate at which SOC stocks are replenished; and (6) suggests that afforestation carried out in the boreal climate zone results in small SOC losses compared with other climate zones, probably because trees grow more slowly under these conditions, although this does not rule out gains over time after the conversion. This study also highlights the importance of the methodological approach used when developing the sampling design, especially the inclusion of the organic layer in the accounting.
  • Authors:
    • Karlen, D. L.
    • Wang, B.
    • Horton, R.
    • Davis, D. D.
    • Fleming, P.
    • Laird, D. A.
  • Source: Geoderma
  • Volume: 158
  • Issue: 3-4
  • Year: 2010
  • Authors:
    • Phillips, R. L.
    • Kronberg, S. L.
    • Gross, J. R.
    • Liebig, M. A.
  • Source: Journal of Environmental Quality
  • Volume: 39
  • Issue: 3
  • Year: 2010
  • Summary: The role of grassland ecosystems as net sinks or sources of greenhouse gases (GHGs) is limited by a paucity of information regarding management impacts on the flux of nitrous oxide (N2O) and methane (CH4). Furthermore, no long-term evaluation of net global warming potential (GWP) for grassland ecosystems in the northern Great Plains (NGP) of North America has been reported. Given this need, we sought to determine net GWP for three grazing management systems located within the NGP. Grazing management systems included two native vegetation pastures (moderately grazed pasture [MGP], heavily grazed pasture [HGP]) and a heavily grazed crested wheatgrass [Agropyron desertorum (Fisch. ex. Link) Schult.] pasture (CWP) near Mandan, ND. Factors evaluated for their contribution to GWP included (i) CO2 emissions associated with N fertilizer production and application, (ii) literature-derived estimates of CH4 production for enteric fermentation, (iii) change in soil organic carbon (SOC) over 44 yr using archived soil samples, and (iv) soil-atmosphere N2O and CH4 fluxes over 3 yr using static chamber methodology. Analysis of SOC indicated all pastures to be significant sinks for SOC, with sequestration rates ranging from 0.39 to 0.46 Mg C ha-1 yr-1. All pastures were minor sinks for CH4 (<2.0 kg CH4-C ha-1 yr-1). Greater N inputs within CWP contributed to annual N2O emission nearly threefold greater than HGP and MGP. Due to differences in stocking rate, CH4 production from enteric fermentation was nearly threefold less in MGP than CWP and HGP. When factors contributing to net GWP were summed, HGP and MGP were found to serve as net CO2equiv. sinks, while CWP was a net CO2equiv. source. Values for GWP and GHG intensity, however, indicated net reductions in GHG emissions can be most effectively achieved through moderate stocking rates on native vegetation in the NGP.
  • Authors:
    • Gross, J. R.
    • Tanaka, D. L.
    • Liebig, M. A.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: The inclusion of cover crops during fallow (i.e., green fallow) may mitigate greenhouse gas (GHG) emissions from dryland cropping systems. An investigation was conducted to quantify the effects of chemical and green fallow on soil organic C (SOC) and CO2, CH4, and N2O flux within spring wheat (Triticum aestivum L.)-fallow (chemical fallow) and spring wheat-safflower (Carthamus tinctorius L.)-rye (Secale cereale L.) (green fallow) under no-till management in west-central North Dakota. Using static chamber methodology, flux measurements were made during 19 mo of the fallow period of each cropping system. Soil samples collected before initiation of flux measurements indicated no difference in SOC in the surface 10 cm between cropping systems. Additionally, differences in gas flux between cropping systems were few. Emission of CO2 was greater under green fallow than chemical fallow during spring thaw until the termination of rye (P = 0.0071). Uptake of atmospheric CH4 was the dominant exchange process during the evaluation period, and was significantly (P = 0.0124) greater under chemical fallow (-2.7 g CH4-C ha-1 d-1) than green fallow (-1.5 g CH4-C ha-1 d-1) following the termination of rye. Cumulative fluxes of CO2, CH4, and N2O did not differ between the chemical- and green-fallow phases during the 19-mo period (P = 0.1293, 0.2629, and 0.9979, respectively). The results from this evaluation suggest there was no net GHG benefit from incorporating a rye cover crop during the fallow phase of a dryland cropping system under no-till management.
  • Authors:
    • Yang, Z.
    • Chen, D.
    • Li, M.
    • Liang, W.
    • Wang, K.
    • Wang, Y.
    • Han, S.
    • Zhou, Z.
    • Zheng, X.
    • Liu, C.
  • Source: Plant and Soil
  • Volume: 332
  • Issue: 1-2
  • Year: 2010
  • Summary: Cotton is one of the major crops worldwide and delivers fibers to textile industries across the globe. Its cultivation requires high nitrogen (N) input and additionally irrigation, and the combination of both has the potential to trigger high emissions of nitrous oxide (N2O) and nitric oxide (NO), thereby contributing to rising levels of greenhouse gases in the atmosphere. Using an automated static chamber measuring system, we monitored in high temporal resolution N2O and NO fluxes in an irrigated cotton field in Northern China, between January 1st and December 31st 2008. Mean daily fluxes varied between 5.8 to 373.0 µg N2O-N m-2 h-1 and -3.7 to 135.7 µg NO-N m-2 h-1, corresponding to an annual emission of 2.6 and 0.8 kg N ha-1 yr-1 for N2O and NO, respectively. The highest emissions of both gases were observed directly after the N fertilization and lasted approximately 1 month. During this time period, the emission was 0.85 and 0.22 kg N ha-1 for N2O and NO, respectively, and was responsible for 32.3% and 29.0% of the annual total N2O and NO loss. Soil temperature, moisture and mineral N content significantly affected the emissions of both gases (p<0.01). Direct emission factors were estimated to be 0.95% (N2O) and 0.24% (NO). We also analyzed the effects of sampling time and frequency on the estimations of annual cumulative N2O and NO emissions and found that low frequency measurements produced annual estimates which differed widely from those that were based on continuous measurements.