Managing soil fertility in organic farming systems   总被引：9，自引：0，他引：9  

C.A. Watson  D. Atkinson  P. Gosling  L.R. Jackson  F.W. Rayns 《Soil Use and Management》2002,18(S1):239-247

Abstract. Complex relationships exist between different components of the organic farm and the quantity and quality of the end products depend on the functioning of the whole system. As such, it is very difficult to isolate soil fertility from production and environmental aspects of the system. Crop rotation is the central tool that integrates the maintenance and development of soil fertility with different aspects of crop and livestock production in organic systems. Nutrient supply to crops depends on the use of legumes to add nitrogen to the system and limited inputs of supplementary nutrients, added in acceptable forms. Manures and crop residues are carefully managed to recycle nutrients around the farm. Management of soil organic matter, primarily through the use of short-term leys, helps ensure good soil structure and biological activity, important for nutrient supply, health and productivity of both crops and livestock. Carefully planned diverse rotations help reduce the incidence of pests and diseases and allow for cultural methods of weed control. As a result of the complex interactions between different system components, fertility management in organic farming relies on a long-term integrated approach rather than the more short-term very targeted solutions common in conventional agriculture.  相似文献   

Perchlorate accumulation in forage and edible vegetation   总被引：8，自引：0，他引：8  

Jackson WA  Joseph P  Laxman P  Tan K  Smith PN  Yu L  Anderson TA 《Journal of agricultural and food chemistry》2005,53(2):369-373

The accumulation of perchlorate in vegetation is becoming a concern, with increasing numbers of sites reporting the presence of perchlorate in groundwater and surface water. This study investigated potential perchlorate uptake and distribution by a variety of forage and edible crops in both the laboratory and the field. Perchlorate concentrations in soybean leaves grown in the greenhouse were significantly higher than perchlorate concentrations in soybean seeds and pods. Perchlorate concentrations in alfalfa grown in sand were significantly lower than those in alfalfa grown in soil. The concentration of perchlorate in tomato was lower in the fruit than the leaves. Commercially grown wheat and alfalfa samples all contained perchlorate, 0.72-8.6 mg/kg of fresh weight (FW) in the wheat stems, 0.71-4.4 mg/kg of FW in the wheat heads, and 2.9 mg/kg of FW in alfalfa. All field garden samples tested (including cucumber, cantaloupe, and tomato) that were irrigated with perchlorate-tainted water contained perchlorate at various concentrations ranging from 0.040 to 1.65 mg/kg of FW. Bioconcentration factors (BCF), ratios of plant fresh weight concentrations to estimated or measured groundwater concentrations [(microg/kg of FW)/microg/L], were all in the same order of magnitude ranging from 215 +/- 126 for wheat stems to 233 +/- 264 for wheat heads and to 380 +/- 89 for alfalfa. BCF for garden fruit samples were much lower (0.5-20). Results from this study highlight the potential for perchlorate exposure by routes other than drinking water.  相似文献   

Parameter estimation with egg production surveys to estimate snapper, Pagrus auratus, biomass in Shark Bay, Western Australia     

Gary Jackson  Yuk W. Cheng 《Journal of Agricultural, Biological & Environmental Statistics》2001,6(2):243-257

Snapper (Pagrusauratus) stocks found inside Shark Bay, Western Australia, are the basis of important recreational fisheries. An evaluation of the daily egg production method for annual snapper stock assessment commenced in 1997. Initial spawning biomass estimates were inconclusive due to wide confidence intervals around egg production in particular. In 1998, more comprehensive surveys were conducted in an effort to improve the accuracy and precision of the estimated parameters. Egg survey design used information on the location of the main spawning areas and spawning times identified in 1997 and employed a systematic stratified adaptive sampling approach. Further refinements to the daily egg production method included use of nonlinear regression and nonparametric bootstrapping techniques. Results are discussed in relation to the precision of parameter estimates, with reference to egg production in particular, and the appropriateness of analytical methods used.  相似文献   

Potential for Enhancement of Biodegradation of Crude Oil in Louisiana Salt Marshes using Nutrient Amendments     

Jackson  W. Andrew  Pardue  John H. 《Water, air, and soil pollution》1999,109(1-4):343-355

Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited to intrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH ₄ ⁺ or NO ₃ ^- ) were determined. Salt marshes have relatively low intrinsic degradation rates (0–3.9% day^-1) of the alkane component (C11-C44) but high rates (8–16% day^-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be most effective if applied as NH ₄ ⁺ in the range of 100-500-N mg kg^-1 of soil producing a pore water range of 100-670-N mg L^-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh.  相似文献   

The roles of subsurface carbon and hydrogen in palladium-catalyzed alkyne hydrogenation     

Teschner D  Borsodi J  Wootsch A  Révay Z  Hävecker M  Knop-Gericke A  Jackson SD  Schlögl R 《Science (New York, N.Y.)》2008,320(5872):86-89

Alkynes can be selectively hydrogenated into alkenes on solid palladium catalysts. This process requires a strong modification of the near-surface region of palladium, in which carbon (from fragmented feed molecules) occupies interstitial lattice sites. In situ x-ray photoelectron spectroscopic measurements under reaction conditions indicated that much less carbon was dissolved in palladium during unselective, total hydrogenation. Additional studies of hydrogen content using in situ prompt gamma activation analysis, which allowed us to follow the hydrogen content of palladium during catalysis, indicated that unselective hydrogenation proceeds on hydrogen-saturated beta-hydride, whereas selective hydrogenation was only possible after decoupling bulk properties from the surface events. Thus, the population of subsurface sites of palladium, by either hydrogen or carbon, governs the hydrogenation events on the surface.  相似文献   

Equatorially dominated magnetic field change at the surface of Earth's core     

Finlay CC  Jackson A 《Science (New York, N.Y.)》2003,300(5628):2084-2086

Slow temporal variations in Earth's magnetic field originate in the liquid outer core. We analyzed the evolution of nonaxisymmetric magnetic flux at the core surface over the past 400 years. We found that the most robust feature is westward motion at 17 kilometers per year, in a belt concentrated around the equator beneath the Atlantic hemisphere. Surprisingly, this motion is dominated by a single wavenumber and persists throughout the observation period. This phenomenon could be produced by an equatorial jet of core fluid, by hydromagnetic wave propagation, or by a combination of both. Discrimination between these mechanisms would provide useful constraints on the dynamics of Earth's core.  相似文献   

Ecological effects of a major oil spill on panamanian coastal marine communities   总被引：1，自引：0，他引：1  

Jackson JB  Cubit JD  Keller BD  Batista V  Burns K  Caffey HM  Caldwell RL  Garrity SD  Getter CD  Gonzalez C  Guzman HM  Kaufmann KW  Knap AH  Levings SC  Marshall MJ  Steger R  Thompson RC  Weil E 《Science (New York, N.Y.)》1989,243(4887):37-44

In 1986 more than 8 million liters of crude oil spilled into a complex region of mangroves, seagrasses, and coral reefs just east of the Caribbean entrance to the Panama Canal. This was the largest recorded spill into coastal habitats in the tropical Americas. Many population of plants and animals in both oiled and unoiled sites had been studied previously, thereby providing an unprecedented measure of ecological variation before the spill. Documenation of the spread of oil and its biological begun immediately. Intertidal mangroves, algae, and associated invertebrates were covered by oil and died soon after. More surprisingly, there was also extensive mortality of shallow subtidal reef corals and infauna of seagrass beds. After 1.5 years only some organisms in areas exposed to the open sea have recovered.  相似文献   

Sequence interpretation. Functional annotation of mouse genome sequences     

Nadeau JH  Balling R  Barsh G  Beier D  Brown SD  Bucan M  Camper S  Carlson G  Copeland N  Eppig J  Fletcher C  Frankel WN  Ganten D  Goldowitz D  Goodnow C  Guenet JL  Hicks G  Hrabe de Angelis M  Jackson I  Jacob HJ  Jenkins N  Johnson D  Justice M  Kay S  Kingsley D  Lehrach H  Magnuson T  Meisler M  Poustka A  Rinchik EM  Rossant J  Russell LB  Schimenti J  Shiroishi T  Skarnes WC  Soriano P  Stanford W  Takahashi JS  Wurst W  Zimmer A;International Mouse Mutagenesis Consortium 《Science (New York, N.Y.)》2001,291(5507):1251-1255

  相似文献   

Organic Glasses: A New Class of Photorefractive Materials     

PM Lundquist  R Wortmann  C Geletneky  RJ Twieg  M Jurich  VY Lee  CR Moylan  DM Burland 《Science (New York, N.Y.)》1996,274(5290):1182-1185

The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties.  相似文献   

Laser ablation and the production of polymer films     

Blanchet GB  Fincher CR  Jackson CL  Shah SI  Gardner KH 《Science (New York, N.Y.)》1993,262(5134):719-721

The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface.  相似文献