Row-crop agriculture is a major source of nitrous oxide (N₂O) globally, and results from recent field experiments suggest that significant decreases in N₂O emissions may be possible by decreasing ...nitrogen (N) fertilizer inputs without affecting economic return from grain yield. We tested this hypothesis on five commercially farmed fields in Michigan, USA planted with corn in 2007 and 2008. Six rates of N fertilizer (0-225 kg N ha⁻¹) were broadcast and incorporated before planting, as per local practice. Across all sites and years, increases in N₂O flux were best described by a nonlinear, exponentially increasing response to increasing N rate. N₂O emission factors per unit of N applied ranged from 0.6% to 1.5% and increased with increasing N application across all sites and years, especially at N rates above those required for maximum crop yield. At the two N fertilizer rates above those recommended for maximum economic return (135 kg N ha⁻¹), average N₂O fluxes were 43% (18 g N₂O-N ha⁻¹ day⁻¹) and 115% (26 g N₂O-N ha⁻¹ day⁻¹) higher than were fluxes at the recommended rate, respectively. The maximum return to nitrogen rate of 154 kg N ha⁻¹ yielded an average 8.3 Mg grain ha⁻¹. Our study shows the potential to lower agricultural N₂O fluxes within a range of N fertilization that does not affect economic return from grain yield.
Whole soil profile assessments of soil C stocks are enormously important for evaluating a soil's potential for sequestering C. Carbon stock measurements are often highly variable, which makes the ...detection of statistically significant differences among different land uses and management systems difficult. A common mistake is to interpret a lack of statistical significance as evidence for the absence of differences. This mistake is costly: failure to identify practices and habitats that accumulate C can affect our understanding of soil C cycling and hide possible sequestration potentials. In this study, we investigated inadequate replication as a major cause of a lack of statistical significance. Power analysis is a well-established statistical tool that allows researchers to infer whether the lack of statistical significance is due to the absence of meaningful differences or due to insufficient replication. We used data from two published studies to illustrate the value of power analysis. In particular, we showed that in these studies the chances of detecting even substantial (e.g., 50%) differences among experimental treatments can be as low as 20 to 60% due to the natural variability in soil C concentrations and stocks. Carbon variability in different soil horizons suggests that statistical analyses of soil C stocks should be conducted separately for each sampled horizon and that conclusions about the profile as a whole should be made based on the individual horizon results. Devising an optimal sampling strategy that identifies the appropriate number of replicates needed to detect significant C change by horizon is essential.
Increasing the potential of soil to store carbon (C) is an acknowledged and emphasized strategy for capturing atmospheric CO
. Well-recognized approaches for soil C accretion include reducing soil ...disturbance, increasing plant biomass inputs, and enhancing plant diversity. Yet experimental evidence often fails to support anticipated C gains, suggesting that our integrated understanding of soil C accretion remains insufficient. Here we use a unique combination of X-ray micro-tomography and micro-scale enzyme mapping to demonstrate for the first time that plant-stimulated soil pore formation appears to be a major, hitherto unrecognized, determinant of whether new C inputs are stored or lost to the atmosphere. Unlike monocultures, diverse plant communities favor the development of 30-150 µm pores. Such pores are the micro-environments associated with higher enzyme activities, and greater abundance of such pores translates into a greater spatial footprint that microorganisms make on the soil and consequently soil C storage capacity.
ABSTRACT
In the two decades since the first extra‐solar planet was discovered, the detection and characterization of extra‐solar planets has become one of the key endeavours in all of modern science. ...Recently, direct detection techniques such as interferometry or coronagraphy have received growing attention because they reveal the population of exoplanets inaccessible to Doppler or transit techniques, and moreover they allow the faint signal from the planet itself to be investigated. Next‐generation stellar interferometers are increasingly incorporating photonic technologies due to the increase in fidelity of the data generated. Here, we report the design, construction and commissioning of a new high‐contrast imager, the integrated pupil‐remapping interferometer, an instrument we expect will find application in the detection of young faint companions in the nearest star‐forming regions. The laboratory characterization of the instrument demonstrated high‐visibility fringes on all interferometer baselines in addition to stable closure phase signals. We also report the first successful on‐sky experiments with the prototype instrument at the 3.9‐m Anglo‐Australian Telescope. Performance metrics recovered were consistent with ideal device behaviour after accounting for expected levels of decoherence and signal loss from the uncompensated seeing. The prospect of complete Fourier coverage coupled with the current performance metrics means that this photonically enhanced instrument is well positioned to contribute to the science of high‐contrast companions.
Understanding how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 is critical to preventing future zoonotic outbreaks before they become the next pandemic. The Huanan ...Seafood Wholesale Market in Wuhan, China, was identified as a likely source of cases in early reports, but later this conclusion became controversial. We show here that the earliest known COVID-19 cases from December 2019, including those without reported direct links, were geographically centered on this market. We report that live SARS-CoV-2-susceptible mammals were sold at the market in late 2019 and that within the market, SARS-CoV-2-positive environmental samples were spatially associated with vendors selling live mammals. Although there is insufficient evidence to define upstream events, and exact circumstances remain obscure, our analyses indicate that the emergence of SARS-CoV-2 occurred through the live wildlife trade in China and show that the Huanan market was the epicenter of the COVID-19 pandemic.
•We studied eight ecosystem service indicators in eight Michigan cropping systems.•None of the systems could maximize the delivery of all ecosystem services.•Trade-offs among ecosystem services ...showed positive and negative relationships.•Tillage, cover crops, and fertilizer usage had large impacts on ecosystem services.
To assess tradeoffs and synergies among different services provided by major ecosystems in agricultural landscapes, we examined agricultural yield, aboveground net primary productivity, global warming impact, soil quality, water conservation, water quality, and plant diversity in eight replicated ecosystems along a management intensity gradient on the same soil type in SW Michigan, USA. Ecosystems included four annual grain systems in a maize–soybean–wheat rotation, two perennial crops (alfalfa and hybrid poplar trees), an early successional community, and a late-successional deciduous forest. The annual grain systems included tilled and no-till treatments both managed with conventional chemical inputs; and reduced input and biologically based treatments both managed with tillage for weed control and leguminous winter cover crops for nitrogen. Radar diagrams illustrated the suite of services provided by each system. We found 13 significant interactions between ecosystem service indicators, seven being positive and six negative. Numerous trade-offs with grain yield were found, suggesting that by focusing on grain yield in these systems, land managers may be neglecting other ecosystem services. Management of nitrogen fertilizer, cover crops, and tillage (no-till) were particularly important determinants for the delivery of multiple ecosystem services.
Soil C sequestration research has historically focused on the top 0 to 30 cm of the soil profile, ignoring deeper portions that might also respond to management. In this study we sampled soils along ...a 10-treatment management intensity gradient to a 1-m depth to test the hypothesis that C gains in surface soils are offset by losses lower in the profile. Treatments included four annual cropping systems in a corn (Zea mays)-soybean (Glycine max)- wheat (Triticum aestivum) rotation, perennial alfalfa (Medicago sativa) and poplar (Populus x euramericana), and four unmanaged successional systems. The annual grain systems included conventionally tilled, no-tillage, reduced-input, and organic systems. Unmanaged treatments included a 12-yr-old early successional community, two 50-yr-old mid-successional communities, and a mature forest never cleared for agriculture. All treatments were replicated three to six times and all cropping systems were 12 yr post-establishment when sampled. Surface soil C concentrations and total C pools were significantly greater under no-till, organic, early successional, never-tilled mid-successional, and deciduous forest systems than in the conventionally managed cropping system (p ≤ 0.05, n = 3–6 replicate sites). We found no consistent differences in soil C at depth, despite intensive sampling (30–60 deep soil cores per treatment). Carbon concentrations in the B/Bt and Bt2/C horizons were lower and two and three times more variable, respectively, than in surface soils. We found no evidence for C gains in the surface soils of no-till and other treatments to be either offset or magnified by carbon change at depth.
Nutrient Imbalances in Agricultural Development Vitousek, P.M; Naylor, R; Crews, T ...
Science (American Association for the Advancement of Science),
06/2009, Letnik:
324, Številka:
5934
Journal Article
Recenzirano
Nutrient additions to intensive agricultural systems range from inadequate to excessive--and both extremes have substantial human and environmental costs.
► Long term changes in soil quality and crop productivity with fertilizer and tillage. ► Soil Quality Index (SQI) developed using Principal Components Approach. ► Improved soil quality in No-till, ...Reduced Input compared to conventional management. ► Conservation management improves nutrient availability, soil stability and structure. ► Soil quality concord with microbial nitrogen processing, nitrogen use and leaching.
Intensively cropped agricultural production systems should be managed to improve soil quality and ecological processes and ultimately strengthen system capacity for sustained biological productivity. We examined the long-term changes (>20 years) in soil quality and productivity with incorporation of ecological management principles in a set of intensively managed row crop systems of the upper Midwest, USA. Replicated experimental treatments include corn (maize)–soybean–wheat cropping systems under four different management regimes: (a) conventional tillage and fertilizer/chemical inputs (
Conventional), (b) no tillage with conventional fertilizer/chemical inputs (
No-till), (c) conventional tillage with ∼30% of conventional fertilizer/chemical inputs and a leguminous cover crop (
Reduced Input), and (d) conventional tillage with no fertilizer/chemical input and a leguminous cover crop (
Organic). Effects of these treatments on soils were compared by developing a soil quality index (SQI) from 19 selected soil health indicators. An old field community maintained in early succession provided a benchmark for comparison. Reduction in tillage or fertilizer (
No-till,
Reduced Input and
Organic) resulted in increased SQI and improved crop production. The
No-till (SQI
=
1.02) and
Reduced Input (SQI
=
1.01) systems outperformed
Conventional management (SQI
=
0.92) in nitrogen availability and use efficiency, soil stability and structure improvement, and microbial nitrogen processing. Improvements in soil quality corresponded with increased primary production and crop yield in these systems, illustrating the value of an ecologically defined SQI for assessing the long-term effects of fertility and tillage management regimes in agricultural production systems.
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