• 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:
    • Shanahan, J. F.
    • Adamchuk, V. I.
    • Kitchen, N. R.
    • Ferguson, R. B.
    • Roberts, D. F.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: Integrating soil-based management zones (MZ) with crop-based active canopy sensors to direct spatially variable N applications has been proposed for improving N fertilizer management of corn ( Zea mays L.). Analyses are needed to evaluate relationships between canopy sensing and soil-based MZ and their combined potential to improve N management. The objectives of this study were to: (i) identify soil variables related to in-season crop canopy reflectance and yield and use these variables to delineate MZ for N fertilizer management; and (ii) compare corn yield response to different N fertilizer treatments for different MZ. Eight N rates (0-274 kg N ha -1 in 39 kg ha -1 increments) were applied in replicated small plots across six irrigated fields in 2007 to 2008 throughout central Nebraska. Soil variables evaluated for MZ delineation included: apparent soil electrical conductivity (EC a), soil optical reflectance, and landscape topography. Crop response to N was determined via active sensor assessments of in-season canopy reflectance (chlorophyll index, CI 590) and grain yield. Relationships between soil and topography data and crop performance were evaluated, with selected soil variables used to delineate two MZ within four of the six fields. Economic benefits to N application according to soil-based MZ were observed in fields with silty clay loam and silt loam soils with substantial relief and eroded slopes. Sensor-based algorithms may need to be adjusted according to MZ to account for differences in crop N response.
  • Authors:
    • Compaore, H.
    • Hien, F.
    • Djagbletey, G.
    • Veenendaal, E.
    • Feldpausch, T. R.
    • Schwarz, M.
    • Schrodt, F.
    • Domingues, T.
    • Bird, M. I.
    • Saiz, G.
    • Diallo, A.
    • Lloyd, J.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 8
  • Year: 2012
  • Summary: We examine the influence of climate, soil properties and vegetation characteristics on soil organic carbon (SOC) along a transect of West African ecosystems sampled across a precipitation gradient on contrasting soil types stretching from Ghana (15°N) to Mali (7°N). Our findings derive from a total of 1108 soil cores sampled over 14 permanent plots. The observed pattern in SOC stocks reflects the very different climatic conditions and contrasting soil properties existing along the latitudinal transect. The combined effects of these factors strongly influence vegetation structure. SOC stocks in the first 2 m of soil ranged from 20 Mg C ha -1 for a Sahelian savanna in Mali to over 120 Mg C ha -1 for a transitional forest in Ghana. The degree of interdependence between soil bulk density (SBD) and soil properties is highlighted by the strong negative relationships observed between SBD and SOC ( r2>0.84). A simple predictive function capable of encompassing the effect of climate, soil properties and vegetation type on SOC stocks showed that available water and sand content taken together could explain 0.84 and 0.86 of the total variability in SOC stocks observed to 0.3 and 1.0 m depth respectively. Used in combination with a suitable climatic parameter, sand content is a good predictor of SOC stored in highly weathered dry tropical ecosystems with arguably less confounding effects than provided by clay content. There was an increased contribution of resistant SOC to the total SOC pool for lower rainfall soils, this likely being the result of more frequent fire events in the grassier savannas of the more arid regions. This work provides new insights into the mechanisms determining the distribution of carbon storage in tropical soils and should contribute significantly to the development of robust predictive models of biogeochemical cycling and vegetation dynamics in tropical regions.
  • Authors:
    • Garcia-Torres, L.
    • Sanchez-Martin, L.
    • Sanz-Cobena, A.
    • Vallejo, A.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 149
  • Year: 2012
  • Summary: Urea has become the predominant source of synthetic nitrogen (N) fertilizer used throughout the world. Among the various available mitigation tools, urease inhibitors like NBPT have the most potential to improve efficiency of urea by reducing N losses, mainly via ammonia volatilization. However, there is a lack of information on the effect of N-(n-butyl) thiophosphoric triamide (NBPT) on other N losses such as gaseous emissions of N 2O and NO and NO 3- leaching. A two-year field experiment using irrigated maize ( Zea mays) crop was carried out under Mediterranean conditions to evaluate the effectiveness of urea coated with NBPT (0.4%, w/w) alone and with both NBPT and nitrification inhibitor dicyandiamide (DCD) (0.4 and 3%, w/w, respectively) to mitigate N 2O-N, NO-N and NO 3--N losses. The different treatments of U, U+NBPT and U+NBPT+DCD were applied to the maize crop in 2009 and then in 2010. The 2010 maize crop followed a fallow period, during which the 2009 crop residues were incorporated into the soil. Two different irrigation regimes were followed each year. In 2009, irrigation was controlled for the first 2 weeks following urea fertilization; whereas, the 2010 crop period was characterized by increased irrigation in the same period. After each treatment application, measurements of the changes in soil mineral N, gaseous emissions of N 2O and NO, nitrate leaching and biomass production were made. N 2O emissions were effectively abated by NBPT and NBPT+DCD and were reduced by 54 and 24%, respectively, in 2009. A reduction in nitrification rate by the inhibitors was also observed during 2009. In 2010 cropping period, NBPT reduced N 2O emissions by 4%; while the combination of NBPT and DCD treatment reduced N 2O emission by 43%. Yield-scaled N 2O emissions were reduced by 50 and 18% by NBPT and the mixture of NBPT+DCD, respectively, in 2009. Applying inhibitors did not have any significant effect on yield-scaled N 2O emissions in the 2010 crop period. Total NO losses from urea were 2.25 kg NO-N ha -1 in the 2009 crop period and 5 times lower in the following year; this may provide an indicator of the prevalence of nitrification as the main process in the production of N 2O in the 2009 maize crop. Most of the NO 3- was lost within the fallow period (i.e. 92, 81 and 75% of the total NO 3- leached for U, U+NBPT and U+NBPT+DCD, respectively), so the incorporation of crop residues was not as effective as expected at reducing these N losses. Our study suggests that the effectiveness of NBPT and combination of NBPT+DCD in reducing N losses from applied urea is influenced by management practices, such as irrigation, and climatic conditions.
  • 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:
    • Kanengieter, R. L.
    • Sleeter, R. R.
    • Bennett, S. L.
    • Reker, R. R.
    • Bouchard, M. A.
    • Sayler, K. L.
    • Sleeter, B. M.
    • Sohl, T. L.
    • Zhu, Z. L.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 153
  • Year: 2012
  • Summary: The Great Plains of the United States has undergone extensive land-use and land-cover change in the past 150 years, with much of the once vast native grasslands and wetlands converted to agricultural crops, and much of the unbroken prairie now heavily grazed. Future land-use change in the region could have dramatic impacts on ecological resources and processes. A scenario-based modeling framework is needed to support the analysis of potential land-use change in an uncertain future, and to mitigate potentially negative future impacts on ecosystem processes. We developed a scenario-based modeling framework to analyze potential future land-use change in the Great Plains. A unique scenario construction process, using an integrated modeling framework, historical data, workshops, and expert knowledge, was used to develop quantitative demand for future land-use change for four IPCC scenarios at the ecoregion level. The FORE-SCE model ingested the scenario information and produced spatially explicit land-use maps for the region at relatively fine spatial and thematic resolutions. Spatial modeling of the four scenarios provided spatial patterns of land-use change consistent with underlying assumptions and processes associated with each scenario. Economically oriented scenarios were characterized by significant loss of natural land covers and expansion of agricultural and urban land uses. Environmentally oriented scenarios experienced modest declines in natural land covers to slight increases. Model results were assessed for quantity and allocation disagreement between each scenario pair. In conjunction with the U.S. Geological Survey's Biological Carbon Sequestration project, the scenario-based modeling framework used for the Great Plains is now being applied to the entire United States.
  • 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:
    • Pavani, M.
    • Susanna, P.
    • Raghvendra, G.
    • Rao, C. S.
    • Sahrawat, K. L.
    • Chander, G.
    • Wani, S. P.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 161
  • Year: 2012
  • Summary: The effects of growing Jatropha in on-farm and on-station degraded lands were evaluated on carbon (C) sequestration and soil properties. Jatropha accumulated and added to soil significant amounts of C (305 kg ha -1 year -1) from the year one itself. Overall, a 3-5-year old plantation added per year around 4000 kg plant biomass equivalent to 1450 kg C ha -1-800 kg C through leaves, 150 kg C through pruned twigs, and 495 kg C as deoiled Jatropha cake. Biodiesel C replacement in the fossil fuel was 230 kg ha -1. Besides adding biomass to the soil, and C replacement in fossil fuel; the standing Jatropha rendered ecosystem service by fixing 5100-6100 kg ha -1 C as the aboveground plus belowground biomass. Carbon additions by Jatropha during 4 years increased C content in the degraded surface soil layer by 19%, resulting in about 2500 kg ha -1 C sequestered. Huge C additions and live root activity under Jatropha increased microbial population, respiration rate and microbial biomass C and N in soil. Along with C additions, 4000 kg ha -1 year -1 plant biomass recycled into the soil 85.5 kg nitrogen, 7.67 kg phosphorus, 43.9 kg potassium, 5.20 kg sulphur, 0.11 kg boron, 0.12 kg zinc and other nutrients. The C additions improved water holding capacity of the soil under Jatropha as compared with the adjacent control soil which increased by 35% at 30 kPa and 21% at 1500 kPa soil water potential.
  • Authors:
    • Khizar, A.
    • Abbasi, M. K.
  • Source: Ecological Engineering
  • Volume: 39
  • Issue: February
  • Year: 2012
  • Summary: Application of organic amendments to soil is an important management strategy for enhancing the restoration of degraded soils and providing better soil conditions to below-ground soil microbial composition and above-ground plant community development. This study was conducted to investigate the effect of organic amendments (poultry manure - PM; white clover residues - WCR), a mineral N fertilizer (urea N - UN), or mixtures of these fertilizers on microbial activity and nitrogen (N) mineralization through both soil analysis (laboratory incubation) and aboveground maize (Zea mays L) growth (pot experiment). In the incubation experiment, soil was amended with PM, WCR, PM + WCR, UN, UN + PM, UN + WCR, and UN + PM + WCR at the rate equivalent to 200 mg N kg(-1) soil. Pot experiment was conducted in a glasshouse using same amendments to examine the response of maize seedlings to these treatments. Organic amendments and UN applied alone or in mixtures increased soil microbial biomass compared to the control. Among N amendments, the highest evaluation of CO2-C (47.7 mg kg(-1) day(-1)), microbial biomass C (434 mg kg) and microbial biomass N (86 mg kg(-1)) were recorded in the UN + PM + WCR while the lowest values were recorded in UN. It is estimated that 9-18% of the applied N had been assimilated into microbial N pool after 105 days. Mineralization of N was higher in the fertilized soil and ranged between 85 and 192 mg N kg(-1) compared with 46 mg N kg(-1) in the control. The net cumulative N mineralized (NCNM) ranged between 43 and 169 mg kg(-1) while the net cumulative N nitrified (NCNN) ranged between 16 and 69%. Combined application of UN + PM + WCR exhibited the highest NCNM and NCNN. On average, percentage conversion of added N into NO3--N was: 21% from organic sources, 40% from UN and 52% from UN + organic sources. The apparent recovery of added N (ANR) from PM, WCR and PM + WCR was 20, 24 and 45%, respectively, while UN, UN + PM, UN + WCR and UN + PM + WCR exhibited 50, 57, 64, and 73% ANR, respectively. Results obtained from the pot experiment (on maize) were consistent with the total mineral N (TMN) released from different amendments and highly significant correlations existed between TMN and plant dry matter yield (r(2) = 0.92) and TMN and N uptake of plants (r(2) = 0.89). The present study demonstrates the existence of substantial amount of N reserve present in organic substrates, which can be transformed into inorganic N pool and can be taken into account as potential sources in the management of the nutrient poor soils and crop growth. (C) 2011 Published by Elsevier B.V.