• Authors:
    • Craine, J. M.
    • Ramirez, K. S.
    • Fierer, N.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) via anthropogenic activities with the added N having potentially important impacts on microbially mediated belowground carbon dynamics. However, a comprehensive understanding of how elevated N availability affects soil microbial processes and community dynamics remains incomplete. The mechanisms responsible for the observed responses are poorly resolved and we do not know if soil microbial communities respond in a similar manner across ecosystems. We collected 28 soils from a broad range of ecosystems in North America, amended soils with inorganic N, and incubated the soils under controlled conditions for 1 year. Consistent across nearly all soils, N addition decreased microbial respiration rates, with an average decrease of 11% over the year-long incubation, and decreased microbial biomass by 35%. High-throughput pyrosequencing showed that N addition consistently altered bacterial community composition, increasing the relative abundance of Actinobacteria and Firmicutes, and decreasing the relative abundance of Acidobacteria and Verrucomicrobia. Further, N-amended soils consistently had lower activities in a broad suite of extracellular enzymes and had decreased temperature sensitivity, suggesting a shift to the preferential decomposition of more labile C pools. The observed trends held across strong gradients in climate and soil characteristics, indicating that the soil microbial responses to N addition are likely controlled by similar wide-spread mechanisms. Our results support the hypothesis that N addition depresses soil microbial activity by shifting the metabolic capabilities of soil bacterial communities, yielding communities that are less capable of decomposing more recalcitrant soil carbon pools and leading to a potential increase in soil carbon sequestration rates.
  • Authors:
    • Schuhmacher, M.
    • Nadal, M.
    • Marti, E.
    • Sierra, J.
    • Roig, N.
    • Domingo, J. L.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 158
  • Year: 2012
  • Summary: Wastewater treatment processes generate highly biodegradable solid wastes. As their fate is an environmental issue of great concern, public administrations promote a sustainable management of urban wastes. The objective of the present study was to analyze the systematic and periodical use, for 16 years, of anaerobically digested sewage sludge as an agricultural fertilizer by assessing the effects on some soil physical-chemical, functional, and ecotoxicological properties. The results showed that the input of sludge enhances soil properties proportionally to the application doses and/or frequency. The organic amendments increased the organic matter content (and its aromaticity), the soil nitrogen, and the microbial activity, improving carbon and nitrogen mineralization processes and some enzymatic functions. However, a maximum dose was identified (40 Mg ha -1 year -1), beyond which soil properties do not improve, and may even worsen. Regarding environmental risks, although the bioluminescent bacteria test showed no toxicity on soil extracts, potential adverse effects such as some potentially toxic elements accumulation, phytotoxicity and the likelihood of groundwater pollution by nitrates or dissolved organic matter should be taken into account. The complementarity of studying soil functioning parameters and ecotoxicological effects, together with the analysis of pollutant content, must be enhanced. This assures a more realistic assessment of long-term effects of sewage sludge-amended soils.
  • Authors:
    • Lauenroth, W. K.
    • Schlaepfer, D. R.
    • Bradford, J. B.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Widespread documentation of positive winter temperature anomalies, declining snowpack and earlier snow melt in the Northern Hemisphere have raised concerns about the consequences for regional water resources as well as wildfire. A topic that has not been addressed with respect to declining snowpack is effects on ecosystem water balance. Changes in water balance dynamics will be particularly pronounced at low elevations of mid-latitude dry regions because these areas will be the first to be affected by declining snow as a result of rising temperatures. As a model system, we used simulation experiments to investigate big sagebrush ecosystems that dominate a large fraction of the semiarid western United States. Our results suggest that effects on future ecosystem water balance will increase along a climatic gradient from dry, warm and snow-poor to wet, cold and snow-rich. Beyond a threshold within this climatic gradient, predicted consequences for vegetation switched from no change to increasing transpiration. Responses were sensitive to uncertainties in climatic prediction; particularly, a shift of precipitation to the colder season could reduce impacts of a warmer and snow-poorer future, depending on the degree to which ecosystem phenology tracks precipitation changes. Our results suggest that big sagebrush and other similar semiarid ecosystems could decrease in viability or disappear in dry to medium areas and likely increase only in the snow-richest areas, i.e. higher elevations and higher latitudes. Unlike cold locations at high elevations or in the arctic, ecosystems at low elevations respond in a different and complex way to future conditions because of opposing effects of increasing water-limitation and a longer snow-free season. Outcomes of such nonlinear interactions for future ecosystems will likely include changes in plant composition and productivity, dynamics of water balance, and availability of water resources.
  • Authors:
    • Ball, B. C.
    • Yamulki, S.
    • Chadwick, D. R.
    • Watson, C. J.
    • Thorman, R.
    • Dobbie, K. E.
    • Smith, K. A.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 93
  • Issue: 2
  • Year: 2012
  • Summary: Nitrous oxide emission factors (EFs) were calculated from measurements of emissions from UK wheat crops and grassland, that were part of a wider research programme on N loss pathways and crop responses. Field studies were undertaken in 2003, 2004 and 2005-a total of 12 site-seasons. Nitrous oxide emissions were measured by the closed static chamber method, following the application of various N fertilizer forms (ammonium nitrate (AN), calcium ammonium nitrate (CAN), urea (UR), urea ammonium sulphate and urea ammonium nitrate) at the recommended rates. Emission factors for the growing season (March-September) ranged from less than 0.1-3.9 %. In the 2nd year, measurements continued at three sites until the following February; the resulting annual EFs were one-third greater, on average, than those for the growing season. There was some evidence that N2O emissions from UR were smaller than from AN or CAN, but when this was adjusted for loss of ammonia by volatilization, there was generally little difference between different forms of N. Emissions from UR modified by the addition of the urease inhibitor nBTPT (UR + UI) were lower than corresponding emissions from nitrate forms, except under conditions where emissions were generally low, even allowing for indirect emissions, suggesting that the use of a urease inhibitor can provide some mitigation of N2O, as well as NH3, emissions. The emission data broadly bear out the relationships obtained in earlier UK studies, showing a strong dependence of N2O emission on soil wetness, temperature and the presence of sufficient mineral N in the soil, which decreases rapidly after N application mainly as a result of plant uptake. Overall net mean EFs for the whole season (after subtracting background emissions from unfertilized controls) covered a range wider than the 0.3-3.0 % range of IPCC (2006).
  • Authors:
    • Storkey, J.
    • Stratonovitch, P.
    • Semenov, M. A.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Predicting the impact of climate change on the damage niche of an agricultural weed at a local scale requires a process-based modelling approach that integrates local environmental conditions and the differential responses of the crop and weed to change. A simulation model of the growth and population dynamics of winter wheat and a competing weed, Sirius 2010, was calibrated and validated for the most economically damaging weed in UK cereals, Alopecurus myosuroides. The model was run using local-scale climatic scenarios generated by the LARS-WG weather generator and based on the HadCM3 projections for the periods 2046-2065 and 2080-2099 to predict the impact of climate change on the population dynamics of the weed and its effect on wheat yields. Owing to rising CO 2 concentration and its effect on radiation use efficiency of wheat, weed-free wheat yields were predicted to increase. The distribution of the weed was predicted to remain broadly similar with a possible northward shift in range. Local-scale variation in the impact of climate change was apparent owing to variation in soil type and water holding capacity. The competitive balance was shifted in favour of the deeper rooted crop under climate change, particularly on sites with lighter soils, owing to more frequent and severe drought stress events. Although the damage niche of A. myosuroides was predicted to reduce under climate change, it is likely that weeds with contrasting physiology, such as C4 species, will be better adapted to future conditions and pose a more serious threat.
  • Authors:
    • Maigne, E.
    • Leger, F.
    • Cahuzac, E.
    • Allaire, G.
    • Teillard, F.
    • Tichit, M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 149
  • Year: 2012
  • Summary: The objective of this study was to map agricultural intensity on the scale of France with spatial resolution adequate for policy targeting. Using the French Farm Accountancy Data Network (FADN), we computed an intensity indicator based on input costs per ha ("IC/ha"). Common variables between the FADN and four other datasets were included in a two steps multinomial regression to estimate the IC/ha value of each Small Agricultural Region ("SAR", units with homogeneous agro-ecological characteristics with mean width=22.4 km). The local indicator of spatial association was used to reveal clusters where SARs with homogeneous intensities were aggregated. We showed that the IC/ha indicator displayed a broad intensity gradient where production types were fairly evenly distributed. Multinomial regression models provided a reliable estimate of the intensity indicator (mean cross-validation error=23%, mean r2=0.7) with SAR resolution. At the scale of France and within the two intensity extremes (500 Euro/ha), SARs were significantly aggregated in several clusters. Most low-input SARs were aggregated into a large cluster ranging across several mountainous regions. Less high-input SARs were significantly aggregated. Our results could be used for infra-regional targeting of conservation policies.
  • Authors:
    • Freney, J. R.
    • Chen, D.
    • Edis, R. E.
    • Turner, D. A.
    • Denmead, O. T.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 93
  • Issue: 2
  • Year: 2012
  • Summary: As farmers in southern Australia typically apply nitrogen (N) to cereal crops by top-dressing with ammonia (NH3) based fertilizer in late winter or early spring there is the potential for large losses of NH3. This paper describes the results of micrometeorological measurements to determine NH3 loss and emission factors following applications of urea, urea ammonium nitrate (UAN), and ammonium sulfate (AS) at different rates to cereal crops at two locations in southern Australia. The amounts of NH3 lost are required for farm economics and management, whilst emission factors are needed for inventory purposes. Ammonia loss varied with fertilizer type (urea > UAN > AS) and location, and ranged from 1.8 to 23 % of N applied. This compares with the emission factor of 10 % of applied N advocated by IPCC ( 2007). The variation with location seemed to be due to a combination of factors including soil texture, soil moisture content when fertilizer was applied and rainfall after fertilizer application. Two experiments at one location, 1 week apart, demonstrated how small, temporal differences in weather conditions and initial soil water content affected the magnitude of NH3 loss. The results of these experiments underline the difficulties farmers face in timing fertilization as the potential for loss, depending on rainfall, can be large.
  • Authors:
    • Perales, H. R.
    • Martinez-Meyer, E.
    • Ureta, C.
    • Alvarez-Buylla, E. R.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: Climate change is expected to be a significant threat to biodiversity, including crop diversity at centers of origin and diversification. As a way to avoid food scarcity in the future, it is important to have a better understanding of the possible impacts of climate change on crops. We evaluated these impacts on maize, one of the most important crops worldwide, and its wild relatives Tripsacum and Teocintes. Maize is the staple crop in Mexico and Mesoamerica, and there are currently about 59 described races in Mexico, which is considered its center of origin. In this study, we modeled the distribution of maize races and its wild relatives in Mexico for the present and for two time periods in the future (2030 and 2050), to identify the potentially most vulnerable taxa and geographic regions in the face of climate change. Bioclimatic distribution of crops has seldom been modeled, probably because social and cultural factors play an important role on crop suitability. Nonetheless, rainfall and temperature still represent a major influence on crop distribution pattern, particularly in rainfed crop systems under traditional agrotechnology. Such is the case of Mexican maize races and consequently, climate change impacts can be expected. Our findings generally show significant reductions of potential distribution areas by 2030 and 2050 in most cases. However, future projections of each race show contrasting responses to climatic scenarios. Several evaluated races show new potential distribution areas in the future, suggesting that proper management may favor diversity conservation. Modeled distributions of Tripsacum species and Teocintes indicate more severe impacts compared with maize races. Our projections lead to in situ and ex situ conservation recommended actions to guarantee the preservation of the genetic diversity of Mexican maize.
  • Authors:
    • Lutzow, M. von
    • Schilling, B.
    • Reischl, A.
    • Haug, S.
    • Hangen, E.
    • Geuss, U.
    • Sporlein, P.
    • Wiesmeier, M.
    • Kogel-Knabner, I.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 7
  • Year: 2012
  • Summary: Precise estimations of soil organic carbon (SOC) stocks are of decided importance for the detection of C sequestration or emission potential induced by land use changes. For Germany, a comprehensive, land use-specific SOC data set has not yet been compiled. We evaluated a unique data set of 1460 soil profiles in southeast Germany in order to calculate representative SOC stocks to a depth of 1 m for the main land use types. The results showed that grassland soils stored the highest amount of SOC, with a median value of 11.8 kg m -2, whereas considerably lower stocks of 9.8 and 9.0 kg m -2 were found for forest and cropland soils, respectively. However, the differences between extensively used land (grassland, forest) and cropland were much lower compared with results from other studies in central European countries. The depth distribution of SOC showed that despite low SOC concentrations in A horizons of cropland soils, their stocks were not considerably lower compared with other land uses. This was due to a deepening of the topsoil compared with grassland soils. Higher grassland SOC stocks were caused by an accumulation of SOC in the B horizon which was attributable to a high proportion of C-rich Gleysols within grassland soils. This demonstrates the relevance of pedogenetic SOC inventories instead of solely land use-based approaches. Our study indicated that cultivation-induced SOC depletion was probably often overestimated since most studies use fixed depth increments. Moreover, the application of modelled parameters in SOC inventories is questioned because a calculation of SOC stocks using different pedotransfer functions revealed considerably biased results. We recommend SOC stocks be determined by horizon for the entire soil profile in order to estimate the impact of land use changes precisely and to evaluate C sequestration potentials more accurately.
  • Authors:
    • Nolan, P.
    • Burke, J.
    • Roth, B.
    • Helmy, M.
    • Osborne, B.
    • Jones, M.
    • Rueangritsarakul, K.
    • Abdalla, M.
    • Smith, P.
    • Williams, M.
  • Source: Water, Air, & Soil Pollution
  • Volume: 223
  • Issue: 8
  • Year: 2012
  • Summary: Field management is expected to influence nitrous oxide (N2O) production from arable cropping systems through effects on soil physics and biology. Measurements of N2O flux were carried out on a weekly basis from April 2008 to August 2009 for a spring sown barley crop at Oak Park Research Centre, Carlow, Ireland. The soil was a free draining sandy loam typical of the majority of cereal growing land in Ireland. The aims of this study were to investigate the suitability of combining reduced tillage and a mustard cover crop (RT-CC) to mitigate nitrous oxide emissions from arable soils and to validate the DeNitrification-DeComposition (DNDC) model version (v. 9.2) for estimating N2O emissions. In addition, the model was used to simulate N2O emissions for two sets of future climate scenarios (period 2021-2060). Field results showed that although the daily emissions were significantly higher for RT-CC on two occasions (p 0.05) on the cumulative N2O flux, compared with the CT treatment, was found. DNDC was validated using N2O data collected from this study in combination with previously collected data and shown to be suitable for estimating N2O emissions (r (2) = 0.70), water-filled pore space (WFPS) (r (2) = 0.58) and soil temperature (r (2) = 0.87) from this field. The relative deviations of the simulated to the measured N2O values with the 140 kg N ha(-1) fertiliser application rate were -36 % for RT-CC and -19 % for CT. Root mean square error values were 0.014 and 0.007 kg N2O-N ha(-1) day(-1), respectively, indicating a reasonable fit. Future cumulative N2O fluxes and total denitrification were predicted to increase under the RT-CC management for all future climate projections, whilst predictions were inconsistent under the CT. Our study suggests that the use of RT-CC as an alternative farm management system for spring barley, if the sole objective is to reduce N2O emissions, may not be successful.