• Authors:
    • Joergensen, R. G.
    • Schweinsberg-Mickan, M. S. Z.
    • Mueller, T.
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 175
  • Issue: 5
  • Year: 2012
  • Summary: A greenhouse rhizobox experiment was carried out to investigate the fate and turnover of 13C- and 15N-labeled rhizodeposits within a rhizosphere gradient from 08?mm distance to the roots of wheat. Rhizosphere soil layers from 01, 12, 23, 34, 46, and 68?mm distance to separated roots were investigated in an incubation experiment (42 d, 15 degrees C) for changes in total C and N and that derived from rhizodeposition in total soil, in soil microbial biomass, and in the 0.05 M K2SO4extractable soil fraction. CO2-C respiration in total and that derived from rhizodeposition were measured from the incubated rhizosphere soil samples. Rhizodeposition C was detected in rhizosphere soil up to 46?mm distance from the separated roots. Rhizodeposition N was only detected in the rhizosphere soils up to 34?mm distance from the roots. Microbial biomass C and N was increased with increasing proximity to the separated roots. Beside 13C and 15N derived from rhizodeposits, unlabeled soil C and N (native SOM) were incorporated into the growing microbial biomass towards the roots, indicating a distinct acceleration of soil organic matter (SOM) decomposition and N immobilization into the growing microbial biomass, even under the competition of plant growth. During the soil incubation, microbial biomass C and N decreased in all samples. Any decrease in microbial biomass C and N in the incubated rhizosphere soil layers is attributed mainly to a decrease of unlabeled (native) C and N, whereas the main portion of previously incorporated rhizodeposition C and N during the plant growth period remained immobilized in the microbial biomass during the incubation. Mineralization of native SOM C and N was enhanced within the entire investigated rhizosphere gradient. The results indicate complex interactions between substrate input derived from rhizodeposition, microbial growth, and accelerated C and N turnover, including the decomposition of native SOM (i.e., rhizosphere priming effects) at a high spatial resolution from the roots.
  • Authors:
    • Klakegg, O.
    • Arnoldussen, A. H.
    • Skjelvag, A. O.
    • Tveito, O. E.
  • Source: Acta Agriculturae Scandinavica, Section A — Animal Science
  • Volume: 62
  • Issue: 4
  • Year: 2012
  • Summary: Models for an holistic analysis of a farm's greenhouse gas (GHG) emissions are available, e.g. HolosNor. They require access to a farm's management data and its soil and climatic conditions. The objective of this investigation was to demonstrate how available soil and climatic data can be used to provide the required inputs of a farm's natural resource base. Soil type recordings from six municipalities representing main agroclimatic zones of Norway were used. By means of a soil moisture model a combined index of soil moisture and temperature was estimated for use in a carbon balance model, also taking crop species into account. Water filled pore space (Wfps) to saturation and soil temperature were estimated for calculation of emission of nitrous oxide. Input variables for calculation of GHG emissions varied considerably among municipalities and among farms therein.
  • Authors:
    • Azooz, R. H.
    • Soon, Y. K.
    • Arshad, M. A.
    • Lupwayi, N. Z.
    • Chang, S. X.
  • Source: AGRONOMY JOURNAL
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Wood ash has the properties to be an effective liming material, and research is needed to compare its effectiveness relative to agricultural lime on acidic agricultural soils. Wood ash at a calcium carbonate rate of 6.72 t ha -1 was compared with an equivalent rate of agricultural lime on a clay loam soil with an initial pH of 4.9. Replicated plots were managed under a barley ( Hordeum vulgare L.)-canola ( Brassica rapa L.)-pea ( Pisum sativum L.) rotation for 4 yr (2002-2005). Soil pH increased in the order of: wood ash=lime > control (without lime or wood ash). Available soil P increased in the order of: wood ash > lime ≥ control. The effect of wood ash and lime application on pH and available P was greatest in the 0- to 5-cm depth, less but still significant in the 5- to 10-cm depth, and not significant below 10 cm. The effect on soil aggregation was: wood ash > lime > control. Averaged over 4 yr, application of wood ash increased grain yields of barley, canola, and pea by 49, 59, and 55%, respectively, compared to a corresponding increase of 38, 31, and 49% by agricultural lime. The increase in crop yield with wood ash compared with lime is attributed partly to increased P availability in wood ash-amended plots. It is concluded that wood ash applied at rates equivalent to agricultural lime improved some soil chemical and physical properties and increased crop production relative to agricultural lime.
  • Authors:
    • Tenuta, M.
    • Sparling, B.
    • Bell,L. W.
    • Entz, M. H.
  • Source: Web Of Knowledge
  • Volume: 158
  • Year: 2012
  • Summary: Soil carbon stocks are useful indicators of both C sequestration capacity and sustainability of agricultural systems. Yet, most investigations have only studied the effects of agricultural management on soil carbon in surface layers (<0.3 m). Current soil organic carbon (SOC), total soil nitrogen (TN) and plant available phosphorus (P Olsen) to a depth of 1.2 m was measured at two long-term (9 and 18 years) farming systems experiments in southern Manitoba, Canada. Both experiments compared an annual-crop rotation, an alfalfa ( Medicago sativa L.)/crop rotation and re-established perennial grassland. At one site the two cropping systems were managed conventionally as well as in adherence to organic farming guidelines, but without manure additions. Due to higher net primary productivity and higher carbon inputs, particularly below ground, SOC stocks (0-120 cm) were 21-65 t C ha -1 higher under the re-established grassland than cropping systems at the clay soil site after 18 years, but not at the site with sandy loam soil after 9 years. On the clay soil, 30-40% of the additional C in the soil profile under the re-established grassland was found below 30 cm indicating the capacity of deep plant roots to sequester C in the sub-soil. Using alfalfa cut for hay in crop rotations did not increase SOC or N stocks compared to annual crop rotations, but plant-available P concentrations were depleted, especially under organic management. SOC was 25-30 t C ha -1 lower under organic than conventionally managed cropping systems, due to lower inputs of plant C (0.8 t C ha -1 yr -1) over the life of the experiment. This highlights that without additional C inputs organic management can reduce SOC compared to conventional cropping systems unless C inputs are maintained which may require manure or compost additions.
  • Authors:
    • Monk, Wendy A.
    • Baird, Donald J.
    • Peters, Daniel L.
    • Armanini, David G.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 1
  • Year: 2012
  • Summary: Agricultural land use can place heavy demands on regional water resources, strongly influencing the quantity and timing of water flows needed to sustain natural ecosystems. The effects of agricultural practices on streamflow conditions are multifaceted, as they also contribute to the severity of impacts arising from other stressors within the river ecosystem. Thus, river scientists need to determine the quantity of water required to sustain important aquatic ecosystem components and ecological services, to support wise apportionment of water for agricultural use. It is now apparent that arbitrarily defined minimum flows are inadequate for this task because the complex habitat requirements of the biota, which underpin the structure and function of a river ecosystem, are strongly influenced by predictable temporal variations in flow. We present an alternative framework for establishing a first-level, regional ecological instream flow needs standard based on adoption of the Indicators of Hydrologic Alteration/Range of Variability Approach as a broadly applicable hydrological assessment tool, coupling this to the Canadian Ecological Flow Index which assesses ecological responses to hydrological alteration. By explicitly incorporating a new field-based ecological assessment tool for small agricultural streams, we provide a necessary verification of altered hydrology that is broadly applicable within Canada and essential to ensure the continuous feedback between the application of flow management criteria and ecological condition.
  • Authors:
    • Netland, J.
    • Brandsaeter, L. O.
    • Sjursen, H.
  • Source: Acta Agriculturae Scandinavica, Section B - Soil & Plant Science
  • Volume: 62
  • Issue: 2
  • Year: 2012
  • Summary: Cover crops can be used to reduce leaching and erosion, introduce variability into crop rotation and fix nitrogen (N) for use by the main crops, less is however known about effects on weeds. The effects on weed seed bank, weed growth and grain yield of 4 years of annual undersown clover and ryegrass alone and in combination, and one of the 4 years with clover or clover + grass as green manure, were studied in oat and spring wheat at two experimental sites in south-eastern Norway. These treatments were compared with no undersown crop (control) and with weed harrowing. In contrast to many results in the literature, the undersown clover in this study did not suppress annual weeds, but fertilized the weeds as well as the cereals. Undersown clover resulted in a statistically significant increase of grain yield at the two sites to 116% and 121% of control. During the 4-year period relative seed bank and density of emerged weed (dominated by Spergula arvensis) increased significantly about 4.5 and 10 times respectively in the undersown clover plots at Apelsvoll. At Kise both ryegrass alone and ryegrass mixed with clover significantly suppressed the weed biomass to 70% and 74% of control respectively. It is concluded that fertilization effects of undersown clover may have dominated and overriden the competitive effects. One whole-season clover green manure did not increase the mean yield, but resulted in a significant drop in seed bank size the following year, because of limited weed establishment in an established ley. Only a slight increase in average weed biomass was observed at one of the two experimental sites. The weed seed bank and the weed biomass were essentially kept at steady state during the experimental period in harrowed plots, but harrowing decreased grain yield significantly at both sites.
  • Authors:
    • Krumhardt, K. M.
    • Kaplan, J. O.
    • Zimmermann, N. E.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: The long residence time of carbon in forests and soils means that both the current state and future behavior of the terrestrial biosphere are influenced by past variability in climate and anthropogenic land use. Over the last half-millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO 2 concentrations, and human induced deforestation and land abandonment. To quantify the importance of these processes, we performed a series of simulations with the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO 2 concentrations. Although land use change was the major control on the carbon inventory of Europe over the last 500 years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability led to temporary sequestration events of up to 3 Pg, whereas increasing atmospheric CO 2 concentrations during the 20th century led to an increase in carbon storage of up to 15 Pg. Anthropogenic land use caused between 25 Pg of carbon emissions and 5 Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12 Pg of carbon at the present day.
  • 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:
    • 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:
    • Klakegg, O.
    • Janzen, H. H.
    • Skjelvag, A. O.
    • Bonesmo, H.
    • Tveito, O. E.
  • Source: Agricultural Systems
  • Volume: 110
  • Issue: July
  • Year: 2012
  • Summary: To increase food production while mitigating climate change, cropping systems in the future will need to reduce greenhouse gas emission per unit of production. We conducted an analysis of 95 arable farms in Norway to calculate farm scale emissions of greenhouse gases, expressed both as CO2 eq per unit area, and CO2 eq per kg DM produced and to describe relationships between the farms' GHG intensities and heir economic efficiencies (gross margin). The study included: (1) design of a farm scale model for net GHG emission from crop production systems; (2) establishing a consistent farm scale data set for the farms with required soil, weather, and farm operation data; (3) a stochastic simulation of the variation in the sources of GHG emission intensities, and sensitivity analysis of selected parameters and equations on GHG emission intensities; and (4) describing relationships between GHG emission intensities and gross margins on farms. Among small seed and grain crops the variation in GHG emissions per kg DM was highest in oilseed (emission intensity at the 75th percentile level was 1.9 times higher than at the 25th percentile). For barley, oats, spring wheat, and winter wheat, emissions per kg DM at the 75th percentile levels were between 1.4 and 1.6 times higher than those at the 25th percentiles. Similar trends were observed for emissions per unit land area. Invariably soil N2O emission was the largest source of GHG emissions, accounting for almost half of the emissions. The second largest source was the off farm manufacturing of inputs (similar to 25%). Except for the oilseed crop, in which soil carbon (C) change contributed least, the on farm emissions due to fuel use contributed least to the total GHG intensities (similar to 10%). The soil C change contributed most to the variability in GHG emission intensities among farms in all crops, and among the sensitivity elasticities the highest one was related to environmental impacts on soil C change. The high variation in GHG intensities evident in our study implies the potential for significant mitigation of GHG emissions. The GHG emissions per kg DM (intensity) decreased with increasing gross margin in grain and oilseed crops, suggesting that crop producers have economic incentives to reduce GHG emissions. (c) 2012 Elsevier Ltd. All rights reserved,