• Authors:
    • Hargreaves, S. K.
    • Venterea, R. T.
    • Parkin, T. B.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 3
  • Year: 2012
  • Summary: Renewed interest in quantifying greenhouse gas emissions from soil has led to an increase in the application of chamber-based flux measurement techniques. Despite the apparent conceptual simplicity of chamber-based methods, nuances in chamber design, deployment, and data analyses can have marked effects on the quality of the flux data derived. In many cases, fluxes are calculated from chamber headspace vs. time series consisting of three or four data points. Several mathematical techniques have been used to calculate a soil gas flux from time course data. This paper explores the influences of sampling and analytical variability associated with trace gas concentration quantification on the flux estimated by linear and nonlinear models. We used Monte Carlo simulation to calculate the minimum detectable fluxes (alpha=0.05) of linear regression (LR), the Hutchinson/Mosier (H/M) method, the quadratic method (Quad), the revised H/M (HMR) model, and restricted versions of the Quad and H/M methods over a range of analytical precisions and chamber deployment times (DT) for data sets consisting of three or four time points. We found that LR had the smallest detection limit thresholds and was the least sensitive to analytical precision and chamber deployment time. The HMR model had the highest detection limits and was most sensitive to analytical precision and chamber deployment time. Equations were developed that enable the calculation of flux detection limits of any gas species if analytical precision, chamber deployment time, and ambient concentration of the gas species are known.
  • Authors:
    • Lecain, D.
    • Prihodko, L.
    • Grosso, S. del
    • Smith, D.
    • Morgan, J.
    • Parton, W.
    • Kelly, R.
    • Lutz, S.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: Net ecosystem productivity (NEP) was measured on shortgrass steppe (SGS) vegetation at the USDA Central Plains Experimental Range in northeastern Colorado from 2001 to 2003. Large year-to-year differences were observed in annual NEP, with >95% of the net carbon uptake occurring during May and June. Low precipitation during the 2002 April to June time period greatly reduced annual net carbon uptake. Large precipitation events (>10 mm day -1) promoted carbon uptake, while small precipitation events (5 mm having a similar increase in respiration (>3.00 g m Cm -2 day -1). In addition, the size of the heterotrophic respiration pulse is independent of both the amount of time since the last rainfall event and the time of occurrence during the growing season.
  • Authors:
    • Brent, L. C.
    • Newman, E. M.
    • Perlman, R.
    • Stanley, R. C.
    • Cerasale, D.
    • Pimentel, D.
    • Mullan, A.
    • Chang, D. T. I.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 161
  • Year: 2012
  • Summary: Annual grain crops are planted on about 70% of the world's cropland and provide 80% of the world's food. Currently annual grains dominate grain production. Perennial grains offer many important opportunities to produce grains in a more environmentally, economically, and energetically sound manner. Thus, major research efforts are needed to develop perennial grains to help feed the growing and malnourished world population. These grains would also aid in diversifying agriculture.
  • 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:
    • Hedtcke, J. L.
    • Kucharik, C. J.
    • Jackson, R. D.
    • Posner, J. L.
    • Sanford, G. R.
    • Lin, T. L.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 162
  • Year: 2012
  • Summary: Soil organic carbon (SOC) is highly sensitive to agricultural land management, so there is a great deal of interest in managing cultivated soils to sequester atmospheric CO 2. In this study we evaluated the influence of six cropping systems on SOC at the Wisconsin Integrated Cropping System Trial (WICST) over a 20-year period. Analysis of SOC on either a concentration or mass per volume of soil basis indicated a significant decline across all of the systems at WICST. While the rotationally grazed pasture system sequestered carbon (C) in the surface 15 cm these gains were offset by losses at depth. Both no-till (NT) practices and inclusion of perennial crops reduced SOC loss, but neither resulted in C sequestration in the soil profile. Results from this study demonstrate the importance of (i) comparing current and initial soil samples when evaluating SOC sequestration and (ii) evaluating SOC changes throughout the soil profile. The losses of SOC at depths below the plow layer point to either a lack of C input from roots, increased oxidative loss at these depths or both.
  • Authors:
    • Berhe, A. A.
    • Sarkhot, D. V.
    • Ghezzehei, T. A.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Amending soils with biochar can have multiple environmental benefits, including improvement in soil physicochemical properties, carbon sequestration, reduction in leaching losses of essential nutrients, and reduction in greenhouse gas (GHG) emissions. This study was conducted to determine the effect of enriched biochar amendments on leaching losses of essential nutrients and GHG emissions from soil. The enriched biochar was prepared by shaking biochar with dairy manure effluent for 24 h, which increased the C and N concentration of biochar by 9.3 and 8.3%, respectively. Incubation and leaching experiments were conducted for 8 wk with three treatments: soil, soil+1% biochar, and soil+1% enriched biochar. Amendment with biochar and enriched biochar relative to unamended soil resulted in 68 and 75% reduction in net nitrification, 221 and 229% reduction in net ammonification, 67 and 68% reduction in cumulative CO 2 flux, respectively, and 26% reduction in cumulative N 2O flux for both biochar treatments. There were no significant differences among treatments in total leaching losses of C, N, and base cations. Our findings suggest that enrichment of biochar with dairy manure effluent can promote C and N storage in soil and provide additional environmental benefits.
  • Authors:
    • Stockert, C. M.
    • Muhammad, S.
    • Alsina, M. M.
    • Schellenberg, D. L.
    • Wolff, M. W.
    • Sanden, B. L.
    • Brown, P. H.
    • Smart, D. R.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: The optimum yield-scaled global warming potential (GWP) of perennial crops on arid land requires effective strategies for irrigation and fertilization. In 2009-2010, N 2O emissions and CH 4 oxidation were measured from an almond [ Prunus dulcis (Mill.) D.A. Webb] production system irrigated with nitrogen (N) fertilizers. Individual plots were selected within a randomized complete block design with fertilizer treatments of urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN). Event-related N 2O emissions from irrigation and fertilization were determined for seasonal periods of post-harvest, winter, spring and summer. Peak N 2O emissions in summer occurred within 24 h after fertilization, and were significantly greater from UAN compared to CAN ( p<0.001). Cumulative N 2O emissions from UAN were on average higher than CAN though not significantly different. Air temperature, water-filled pore space (WFPS), soil ammonium (NH 4+) and soil nitrate (NO 3-) showed significant positive correlation with N 2O emissions and significant negative correlation was found for the number of days after fertilization (DAF). The percentage of N 2O loss from N fertilizer inputs was 0.23% for CAN and 0.35% for UAN while CH 4 oxidation offset 6.0-9.3% of N 2O emissions. Total kernel yield was not significantly different between fertilizer treatments. Yield-scaled GWP for almond from CAN (60.9 kg CO 2eq Mg -1) and UAN (91.9 kg CO 2eq Mg -1) represent the first report of this metric for a perennial crop. These results outline effective irrigation and fertilization strategies to optimize yield-scaled GWP for almond on arid land.
  • 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:
    • Woodroof, R. H.
    • Watts, D. W.
    • Busscher, W. J.
    • Novak, J. M.
    • Das, K. C.
    • Harris, K.
    • Gaskin, J. W.
    • Schomberg, H. H.
    • Lima, I. M.
    • Ahmedna, M.
    • Rehrah, D.
    • Xing, B. S.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Interest in the use of biochar from pyrolysis of biomass to sequester C and improve soil productivity has increased; however, variability in physical and chemical characteristics raises concerns about effects on soil processes. Of particular concern is the effect of biochar on soil N dynamics. The effect of biochar on N dynamics was evaluated in a Norfolk loamy sand with and without NH 4NO 3. High-temperature (HT) (≥500°C) and low-temperature (LT) (≤400°C) biochars from peanut hull ( Arachis hypogaea L.), pecan shell ( Carya illinoinensis Wangenh. K. Koch), poultry litter ( Gallus gallus domesticus), and switchgrass ( Panicum virgatum L.) and a fast pyrolysis hardwood biochar (450-600°C) were evaluated. Changes in inorganic, mineralizable, resistant, and recalcitrant N fractions were determined after a 127-d incubation that included four leaching events. After 127 d, little evidence of increased inorganic N retention was found for any biochar treatments. The mineralizable N fraction did not increase, indicating that biochar addition did not stimulate microbial biomass. Decreases in the resistant N fraction were associated with the high pH and high ash biochars. Unidentified losses of N were observed with HT pecan shell, HT peanut hull, and HT and LT poultry litter biochars that had high pH and ash contents. Volatilization of N as NH 3 in the presence of these biochars was confirmed in a separate short-term laboratory experiment. The observed responses to different biochars illustrate the need to characterize biochar quality and match it to soil type and land use.
  • Authors:
    • Rosenheim, J. A.
    • Segoli, M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 150
  • Year: 2012
  • Summary: The intensification of agriculture, including the increase in the spatial extent of monocultures, is widely expected to result in an increase in crop damage by herbivorous pests. The theoretical basis for this expectation is, however, unclear. We used a simulation model to explore the relationship between the field size of monocultural crops and season-long mean expected pest densities. We investigated how the underlying relationship between field size and pest densities might be influenced by the presence/absence of an effective natural enemy; by the relative dispersal abilities of the pest and natural enemy; by the ability of the pest and natural enemy to overwinter within the crop habitat; and by the pest's rate of reproduction in the crop. Our model predicts that the relationship between field size and pest densities may, under commonly satisfied conditions, assume any of several forms (positive, negative, hump-shaped, or essentially constant), depending on the biology of the organisms. Each of the underlying relationships between field size of monocultural crops and expected pest densities may motivate adoption of a different set of pest management tactics. Whereas positive relationships motivate tactics that facilitate early natural enemy colonization of the interior of large monocultures (e.g., by supplementing food resources within the crop), negative relationships may instead motivate a suite of farm-design approaches that reduce pest colonization of crop interiors by achieving larger functional field sizes (e.g., aggregating multiple fields of the same crop).