• Authors:
    • Armstrong, R.
    • Norton, R.
    • Chen, D. l.
    • Lam, S. K.
  • Source: Nutrient Cycling in Agroecosytems
  • Volume: 92
  • Issue: 2
  • Year: 2012
  • Summary: There are few reports on the effects of atmospheric carbon dioxide concentration ([CO2]) on fertilizer N recovery by crops under open-air conditions. This study was conducted at the Australian Grains Free-Air CO2 Enrichment (AGFACE) facility in southern Australia to investigate the effects of elevated [CO2] (550 mu mol mol(-1)) on growth, N uptake and fertilizer N-15 recovery by spring wheat (Triticum aestivum L. cv. Yitpi) over a 2-year period. N-15-enriched (10.22 atom%) granular urea was applied to microplots at 50 kg N ha(-1) at varying seasonal rainfall and temperature scenarios (simulated by supplementary irrigation and late sowing) for three experimental periods [2008 normal sowing (2008NS), 2008 late sowing (2008LS) and 2009 normal sowing (2009NS)]. Elevated [CO2] increased wheat biomass (27-58%), N uptake (18-44%) and amount of plant N derived from soil (20-50%) at 2008NS and 2009NS (rainfed), but the effect was not apparent at 2008LS (hotter and drier) and supplementary irrigated plots for 2009NS (above-average rainfall). Tissue N concentration and N derived from fertilizer were unaffected by elevated [CO2] in any experimental period. Irrespective of [CO2], grain yield and whole plant fertilizer N uptake was 37-94 and 13-609%, respectively, higher under supplementary irrigated plots than that in rainfed counterparts. These results indicate that more fertilizer N will need to be applied to this wheat production zone under future [CO2] environments, and yield gains in hotter and drier climates will be lower than those in higher rainfall zones.
  • Authors:
    • Sheppard, L. J.
    • Ostle, N.
    • Mills, R.
    • Mcnamara, N. P.
    • Jones, T.
    • Jones, S. K.
    • Gray, A.
    • Gaiawyn, J.
    • Fowler, D.
    • Evans, C.
    • Drewer, J.
    • Dinsmore, K. J.
    • Cooper, M. D. A.
    • Burden, A.
    • Levy, P. E.
    • Skiba, U.
    • Sowerby, A.
    • Ward, S. E.
    • Zielinski, P.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 5
  • Year: 2012
  • Summary: Nearly 5000 chamber measurements of CH 4 flux were collated from 21 sites across the United Kingdom, covering a range of soil and vegetation types, to derive a parsimonious model that explains as much of the variability as possible, with the least input requirements. Mean fluxes ranged from -0.3 to 27.4 nmol CH 4 m -2 s -1, with small emissions or low rates of net uptake in mineral soils (site means of -0.3 to 0.7 nmol m -2 s -1) and much larger emissions from organic soils (site means of -0.3 to 27.4 nmol m -2 s -1). Less than half of the observed variability in instantaneous fluxes could be explained by independent variables measured. The reasons for this include measurement error, stochastic processes and, probably most importantly, poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. When temporal variation was accounted for, and the fluxes averaged at larger spatial scales, simple models explained up to ca. 75% of the variance in CH 4 fluxes. Soil carbon, peat depth, soil moisture and pH together provided the best sub-set of explanatory variables. However, where plant species composition data were available, this provided the highest explanatory power. Linear and nonlinear models generally fitted the data equally well, with the exception that soil moisture required a power transformation. To estimate the impact of changes in peatland water table on CH 4 emissions in the United Kingdom, an emission factor of +0.4 g CH 4 m -2 yr -1 per cm increase in water table height was derived from the data.
  • Authors:
    • Kunkel, K.
    • Reddy, K. R.
    • Gao, W.
    • Xu, M.
    • Liang, X. Z.
    • Schmoldt, D. L.
    • Samel, A. N.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Climate variability and changes affect crop yields by causing climatic stresses during various stages of the plant life cycle. A crop growth model must be able to capture the observed relationships between crop yields and climate stresses before its credible use as a prediction tool. This study evaluated the ability of the geographically distributed cotton growth model redeveloped from GOSSYM in simulating U.S. cotton ( Gossypium hirsutum L.) yields and their responses to climate stresses during 1979 to 2005. Driven by realistic climate conditions, the model reproduced long-term mean cotton yields within 10% of observations at the 30-km model resolution across virtually the entire U.S. Cotton Belt and correctly captured the critical dependence of their geographic distributions on regional climate characteristics. Significant correlations between simulated and observed interannual variations were found across 87% of the total harvest grids. The model also faithfully represented the predictive role of July to August air temperature and August to September soil temperature anomalies on interannual cotton yield changes on unirrigated lands, with a similar but weaker predictive signal for irrigated lands as observed. The modeled cotton yields exhibited large, positive correlations with July to August leaf area index. These results indicate the model's ability to depict the regional impact of climate stresses on cotton yields and suggest the potential predictive value of satellite retrievals. They also provide a baseline reference for further model improvements and applications in the future study of climate-cotton interactions.
  • Authors:
    • Lin, X. M.
    • Hubbard, K. G.
    • Yang, X. G.
    • Liu, Z. J.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 11
  • Year: 2012
  • Summary: Northeast China (NEC) is not only one of the major agricultural production areas in China, but it is also the most susceptible to climate variability. This led us to investigate the impact of climate change on maize potential yield and yield gaps in this region, where maize accounts for about 30% of the nation's production. The APSIM-Maize model was calibrated and validated for maize phenology and yields. The validated model was then used to estimate potential yields, rain-fed potential yields, and yield gaps for assessing the climate impacts on maize productivity in NEC. During maize growing seasons from 1981 to 2010, the analysis indicates a warming trend all across NEC, whereas the trends in solar radiation and total precipitation tended to decrease. When the same hybrid was specified in APSIM for all years, a simulated increase of maximum temperature resulted in a negative impact on both potential yield and rain-fed potential yield. A simulated increase in minimum temperature produced no significant changes in potential or rain-fed potential yield. However, the increase of minimum temperature was shown to result in a positive impact on the on-farm yield, consistent with our finding that farmers adopted longer season hybrids for which the increase in minimum temperature provided better conditions for germination, emergence, and grain filling during night time. The gap between potential and rain-fed potential yields was shown to be larger at locations with lower seasonal precipitation (<500 mm). Our results indicate that regions with the largest yield gaps between rain-fed potential and on-farm yields were located in the southeast of NEC. Within NEC, on-farm maize yields were, on average, only 51% of the potential yields, indicating a large exploitable yield gap, which provides an opportunity to significantly increase production by effective irrigation, fertilization, herbicide, and planting density in NEC.
  • Authors:
    • Nyamangara, J.
    • Wuta, M.
    • Mapanda, F.
    • Rees, R. M.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 94
  • Issue: 1
  • Year: 2012
  • Summary: Agricultural efforts to end hunger in Africa are hampered by low fertilizer-use-efficiency exposing applied nutrients to losses. This constitutes economic losses and environmental concerns related to leaching and greenhouse gas emissions. The effects of NH4NO3 (0, 60 and 120 kg N ha(-1)) on N uptake, N-leaching and indirect N2O emissions were studied during three maize (Zea mays L.) cropping seasons on clay (Chromic luvisol) and sandy loam (Haplic lixisol) soils in Zimbabwe. Leaching was measured using lysimeters, while indirect N2O emissions were calculated from leached N using the emission factor methodology. Results showed accelerated N-leaching (3-26 kg ha(-1) season(-1)) and N-uptake (10-92 kg ha(-1)) with N input. Leached N in groundwater had potential to produce emission increments of 0-94 g N2O-N ha(-1) season(-1) on clay soil, and 5-133 g N2O-N ha(-1) season(-1) on sandy loam soil following the application of NH4NO3. In view of this short-term response intensive cropping using relatively high N rate may be more appropriate for maize in areas whose soils and climatic conditions are similar to those investigated in this study, compared with using lower N rates or no N over relatively larger areas to attain a targeted food security level.
  • Authors:
    • Devienne, S.
    • Delaby, L.
    • Durand, P.
    • Raimbault, T.
    • Mabon, F.
    • Ruiz, L.
    • Moreau, P.
    • Vertes, F.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 147
  • Year: 2012
  • Summary: Integrated assessment tools are used ever more frequently for solving new environmental, social, and economic challenges related to agriculture sustainability. This is particularly relevant in ecologically vulnerable areas, where mitigation options include a complete redefinition of farming systems. This paper presents an assessment of mitigation options of a coastal agricultural watershed affected by algal proliferations (Lieue de Greve, western France). We developed a methodology based on two existing assessment approaches, an agrarian system diagnosis and an environmental assessment, to identify connections between farming systems and risky nitrogen-agricultural practices and to explore potential ways to reduce the environmental impact of farms while respecting their economic viability and technical feasibility. To understand the functioning of farming systems and calculate key indicators of economic performance, the agrarian system diagnosis combines landscape, historical, and techno-economic aspects of a farm. The environmental assessment includes (i) calculation of farm-gate nitrogen (N) budgets and N-use efficiency and (ii) use of a spatially explicit biophysical model, which simulates the effect of agricultural practices on water and N dynamics at the watershed scale and on N fluxes at the outlet. At the farm scale, the main outputs of the approach were (i) the identification of 11 farming-system types and factors influencing them in the past and present, (ii) the assessment of their techno-economic performances and (iii) for the main dairy systems, the assessment of their potential environmental impacts. Insights about the capacity of some systems to adapt to new constraints linked with environmental objectives were also brought out. Grass-based systems appeared to be the best alternative for existing farming systems since they display good economic results while limiting N emission risks. Scenarios of changes in agricultural practices at the watershed scale were tested with the biophysical model, comparing them to a reference scenario based on the continuation of current agricultural practices. The main results indicated that: (i) current water quality was in equilibrium with current agricultural practices, (ii) the response time of the watershed to changes in agricultural practices was relatively short (6-7 years) and (iii) the expansion of an agro-environmental incentive based on low-input practices and grass-based fodder proposed by local stakeholders to the whole watershed would result in a significant decrease in N fluxes but would not fulfill water-quality objectives. This integrated assessment approach demonstrated its ability to promote the emergence of mitigation solutions and to improve decision support.
  • Authors:
    • Ruser, R.
    • Muller, T.
    • Fiedler, S.
    • Buegger, F.
    • Palmer, I.
    • Pfab, H.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 150
  • Year: 2012
  • Summary: Arable soils are a major source of the climate relevant trace gas nitrous oxide (N 2O). Although N 2O emissions from soils increase with the amount of N-fertilizer, there is still a lack of data for intensively fertilized systems, such as vegetable production. We investigated the effect of an ammonium sulfate nitrate (ASN) fertilization either placed or broadcast applied combined with a nitrification inhibitor (3,4-dimethylepyrazole phosphate (DMPP)) on soil surface N 2O fluxes as compared to conventional broadcast ASN fertilization in a lettuce-cauliflower rotation over two years of measurement. Except for a lower cauliflower yield in the second experimental year with placed fertilization, no differences in yields between the fertilized treatments were observed. Annual cumulative N 2O emissions of the conventionally fertilized treatment were 8.8 and 4.7 kg N 2O-N ha -1 yr -1 for the first and second experimental year, respectively, indicating a high inter-annual variability. The addition of the nitrification inhibitor significantly reduced N 2O emissions during the cropping season and also during the winter period, resulting in an annual reduction of 45 and 40% as compared to the conventionally fertilized (CONV) treatment. The reason for the lower N 2O release in the DMPP treatment as compared to the conventionally fertilized treatment remained unclear. Since we did not find any significant differences in the mineral N pools during periods with distinctive inhibition, this can be ruled out as reason for the lower N 2O release in the DMPP treatment. We found lower soil respiration in the DMPP treatment during several months starting about six weeks after fertilizer application. In contrast to the treatment with nitrification inhibitor, the placed fertilization as an N-depot (fertilizer bands inserted into the soil) did not reduce annual N 2O emissions, although the ratio of ammonium (NH 4+) to nitrate (NO 3-) in the first weeks after N-application indicate inhibition of nitrification in the fertilizer depot. We assume that, even though NH 4+ concentrations in the depots were high, toxicity was not sufficient for a complete inhibition of microbial activity in the surrounding of the depots, resulting in considerable N 2O production. The emission factors calculated for CONV treatment were 1.6 and 0.8% for the first and second experimental year, respectively. For the treatment with nitrification inhibitor (NI), they were only 0.9 and 0.5%; for the treatment with placed fertilization as an N-depot (DEPOT) 2.0 and 0.8%. They were thus within the range proposed by the guidelines of the IPCC (2006). However, although the N-input related N 2O emission factors were within the range proposed by the guidelines of the IPCC, the absolute N 2O emissions from the intensively fertilized vegetable field were high. For effective, but environmentally sound vegetable production, a deeper understanding of nitrification inhibitory strategies is necessary.
  • Authors:
    • Goulding, K. W. T.
    • Macdonald, A. J.
    • Coleman, K.
    • Chambers, B. J.
    • Bhogal, A.
    • Powlson, D. S.
    • Whitmore, A. P.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 146
  • Issue: 1
  • Year: 2012
  • Summary: Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble. The average annual increase in SOC deriving from reduced tillage was 310 kg C180 kg C ha -1 yr -1. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N 2O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha -1 yr -1 t -1 dry solids added) by on average 6020 (farm manures), 18024 (digested biosolids), 5015 (cereal straw), 6010 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha -1 yr -1) but outweighed by N 2O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N 2O emission.
  • Authors:
    • Steffens, D.
    • Qayyum, M. F.
    • Reisenauer, H. P.
    • Schubert, S.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Application of biochars to soils may stabilize soil organic matter and sequester carbon (C). The objectives of our research were to study in vitro C mineralization kinetics of various biochars in comparison with wheat straw in three soils and to study their contribution to C stabilization. Three soils (Oxisol, Alfisol topsoil, and Alfisol subsoil) were incubated at 25°C with wheat straw, charcoal, hydrothermal carbonization coal (HTC), low-temperature conversion coal (LTC), and a control (natural organic matter). Carbon mineralization was analyzed by alkali absorption of CO 2 released at regular intervals over 365 d. Soil samples taken after 5 and 365 d of incubation were analyzed for soluble organic C and inorganic N. Chemical characterization of biochars and straw for C and N bonds was performed with Fourier transformation spectroscopy and with the N fractionation method, respectively. The LTC treatment contained more N in the heterocyclic-bound N fraction as compared with the biochars and straw. Charcoal was highly carbonized when compared with the HTC and LTC. The results show higher C mineralization and a lower half-life of straw-C compared with biochars. Among biochars, HTC showed some C mineralization when compared with charcoal and LTC over 365 d. Carbon mineralization rates were different in the three soils. The half-life of charcoal-C was higher in the Oxisol than in the Alfisol topsoil and subsoil, possibly due to high Fe-oxides in the Oxisol. The LTC-C had a higher half-life, possibly due to N unavailability. We conclude that biochar stabilization can be influenced by soil type.
  • Authors:
    • Herrmann, A.
    • Techow, A.
    • Pacholski, A.
    • Quakernack, R.
    • Taube, F.
    • Kage, H.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 160
  • Year: 2012
  • Summary: Anaerobic co-fermentation of animal slurries and crop silages leads to new types of biogas residues with an uncertain fertilizer value. Ammonia volatilization losses and crop productivity after supplying co-fermented biogas residues were investigated at a marshland site in Northern Germany. Due to the ecological risks of monocultures, maize ( Zea mays) in monoculture as the dominant biogas crop in the marsh was tested against a crop rotation (maize, wheat ( Triticum aestivum), Italian ryegrass ( Lolium multiflorum)) and perennial ryegrass ( Lolium perenne). Biogas residues, applied by trail hoses, and CAN (mineral fertilizer) were used as nitrogen fertilizers. Ammonia losses at all application dates were investigated by an approach including passive flux samplers and a calibrated dynamic chamber method. Simultaneously a micrometeorological technique was used as a reference. A comparison of methods showed a close correlation ( r2=0.92) between micromet and passive flux sampler techniques. Ammonia volatilization losses (on average 15% NH 4+-N applied) occurred mainly within the first 10 h. Concomitant with high ammonia losses, a significant yield depression of 5 t DM ha -1 for ryegrass fertilized by biogas residues compared to CAN was observed. Little or no affect of biogas was observed for maize and wheat. The crop rotation had yields (34 t DM ha -1 2 year -1) that were comparable with the maize monoculture (31 t DM ha -1 2 year -1).