REDUCING SHALLOW LANDSLIDE OCCURRENCE IN PASTORAL HILL COUNTRY USING WIDE‐SPACED TREES     

G. B. Douglas  I. R. Mcivor  A. K. Manderson  J. P. Koolaard  M. Todd  S. Braaksma  R. A. J. Gray 《Land Degradation \u0026amp; Development》2013,24(2):103-114

Shallow landslides occur globally on soil‐mantled hilly and mountainous terrain. In New Zealand, they are a nation‐wide problem, particularly on pastoral hill country grazed by livestock. On these landscapes, trees are planted at low densities, often <70 stems per hectare (sph), to reduce landslide occurrence, but there has been limited quantification of their effectiveness in this role. This study determined the reduction in landslide occurrence at 65 sites planted with spaced trees (53 × Populus, 6 × Salix, 6 × Eucalyptus) following rainstorm events. Sites had a mean slope angle of 27 degrees and soils were predominantly silt or sand‐loams. Tree density across all sites was 32–65 sph, height was 8–43 m, canopy radius was 1–10 m and trunk diameter was 18–99 cm. Trees reduced landslide occurrence by 95 per cent compared to paired pasture control sites (0·4 per cent vs. 7·9 per cent scar area, respectively), and scars occurred on fewer sites with trees than pasture (10 vs. 45). For the 10 tree sites with scars, their area was <3·5 per cent, except at one site where it was 11·3 per cent. There were no significant differences between species in their effectiveness in reducing landslide occurrence. Analyses were partially successful in discriminating between sites with and without shallow landslides and identified some attributes with potentially useful discriminatory power. Aspect, mean slope angle and tree density did not feature significantly in the analyses because they were homogeneous across site groups. The study verified the large benefit from wide‐spaced tree planting on sites susceptible to shallow landslides. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Drip fertigation with nitrogen and potassium and postharvest susceptibility to bacterial soft rot of bell peppers     

Sergio J. Carballo  Sylvia M. Blankenship  Douglas C. Sanders  David F. Ritchie 《Journal of plant nutrition》2013,36(7):1175-1191

In 1991 and 1992, drip irrigation was used to apply various rates and timings of nitrogen (N) and potassium (K) to black polyethylene plastic‐mulched bell pepper (Capsicum annuum L.) to determine the effect on fruit quality and susceptibility to postharvest bacterial soft rot (Ervinia carotovora subsp. carotovora). Neither rate nor application timing affected total yield in either year. In 1991, the high fertilizer rate (266–309 kg/ha of N and K, respectively) increased class 1 yield in the first harvest and reduced total discards. In 1992, a year with a colder than average spring, the low fertilizer rate (70–81 kg/ha of NK) increased class 1 yield in the first harvest. Mid‐ or late‐season fertigation produced more second harvest yield and less discards than the first harvest in 1991, but not in 1992. Fruits of plants fertilized with high N and K rates had greater N and dry matter concentration. No differences in color or wall thickness at harvest were detected among treatments. Stored fruits turned red slower with the late season low fertilizer rate. There were no differences in rate of weight loss during storage at 10°C. No differences in progression of bacterial soft rot were detected among treatments in 1991, but the higher fertigation rates or late timing application increased resistance in 1992.  相似文献   

Effects of plant age on nitrogen uptake and distribution by greenhouse plants     

Touria El‐Jaoual  Douglas Cox 《Journal of plant nutrition》2013,36(5):1055-1066

Water‐soluble nitrogen (N) fertilizer is intensively used in greenhouse crop production. Any N not used by a crop is subject to leaching as nitrate (NO₃‐N), which may pollute groundwater. A close correlation between N supply and N uptake by plants would increase the efficiency of N fertilization and minimize the possibility of NO₃‐N pollution. The objectives of this study were to measure N uptake by American marigold (Tagetes erecta L. ‘First Lady') and New Guinea Impatiens (NGI) (Impatiens hawkeri Bull. ‘Selenia') during growth, to determine the effect of plant age on N uptake, to determine if the two species have a preference for NO₃‐N or ammonium (NH₄‐N), and to determine the total N required for 70 days of growth.The plants were grown in solution culture using solutions supplying 120 mg each of NO₃‐N and NH₄‐N. At ten day intervals, six cultures were chosen at random for nutrient solution analysis and plant sampling for dry weight and tissue analysis. Nitrate‐N uptake was greater than NH₄‐N uptake throughout the experiment for both marigold and NGI. Total N uptake by marigold was greater during the first 50 days after transplanting with maximum N uptake during the period 30 to 50 days. In contrast, N uptake by NGI was greater during the period 40 to 70 days after transplanting. Maximum N uptake for NGI occurred during the period 60 to 70 days. Results of this study suggest that early N fertilization of marigold could be more important for their growth and quality than N applied later. For NGI, N fertilization later in the crop's development appears to be more important than early on. The total N absorbed by marigold during the experiment was 1.1 gm N plant^‐1; for NGI the quantity was 0.5 gm N plant‐¹.  相似文献   

Assessing the Value of Using a Remote Sensing-Based Evapotranspiration Map in Site-Specific Management     

Umakant Mishra  David Clay  Todd Trooien  Kevin Dalsted  Douglas Malo  C. G. Carlson 《Journal of plant nutrition》2013,36(7):1188-1202

ABSTRACT

In the glaciated regions of the northern Great Plains, water - either too much or too little - influences soil development, carbon storage, and plant productivity. Integrating site-specific water variability information directly into management is difficult. Simulation models that employ remotely sensed data can generate hard to measure values such as evapotranspiration (ET). This information can be used to identify management zones. The objective of this study was to determine if the METRIC (Mapping Evapotranspiration at High Resolution and with Internalized Calibration) model, which uses weather station and remote sensing data can be used as a tool in site-specific management. This study was conducted on a 65 ha corn (Zea mays L.) field located in east central South Dakota. The METRIC model used Landsat 7 data collected on August 4, 2001 to calculate ET values with spatial resolution of 30 m. ET values were correlated with corn yield (r = 0.85??), apparent electrical conductivity (EC_a; r = 0.71??), soil organic carbon (SOC; r = 0.32?), and pH (r = 0.28?). In the footslope positions, high ET values were associated with high corn yields, SOC, EC _a , and pH values, while in the summit/shoulder areas low ET values were associated with low yields, SOC, EC_a, and pH values. The strong relationship between ET and productivity was attributed to landscape processes that influenced plant available water, which in turn influenced productivity. Cluster analysis of the ET and EC data showed that these data bases complimented each other. Remote sensing-based ET data was most successful in identifying areas where water stress reduced corn yields, while EC_a was most successful in identifying high yielding management zones. Findings from this study suggest that remote sensing-based ET estimates can be used to improve management zone delineation.  相似文献   

Detection of Leptospira spp. in wildlife reservoir hosts in Ontario through comparison of immunohistochemical and polymerase chain reaction genotyping methods     

Karen E. Shearer  Michael J. Harte  Davor Ojkic  Josepha DeLay  Douglas Campbell 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(3):240-248

A total of 460 kidney samples from wildlife (beavers, coyotes, deer, foxes, opossums, otters, raccoons, skunks) were obtained from road-kill and hunter/trapper donations in Ontario between January 2010 and November 2012. The objectives of the study were to detect Leptospira spp. by immunohistochemistry and polymerase chain reaction (PCR), to map presence of leptospires in wildlife relative to livestock and human populations, and to characterize positive samples by sequencing and comparison to leptospires known to affect domestic animals and humans. The proportion of samples that tested positive ranged from 0% to 42%, with the highest rates in skunks and raccoons. Leptospira spp. were present in kidneys of wildlife across Ontario, particularly in areas of high human density, and areas in which livestock populations are abundant. The PCR was too weak in most samples to permit genotyping and examination of the relationship between the leptospires found in this study and those affecting domestic animals and humans.  相似文献   

Effects of different dietary arachidonic acid : docosahexaenoic acid ratios on phospholipid fatty acid compositions and prostaglandin production in juvenile turbot (Scophthalmus maximus)   总被引：1，自引：0，他引：1  

J. Gordon Bell  John D. Castell  Douglas R. Tocher  Fiona M. MacDonald  John R. Sargent 《Fish physiology and biochemistry》1995,14(2):139-151

Five purified diets containing AA (20:4n-6) at 0.02–0.78% dry weight and DHA (22:6n-3) at 0.93–0.17% dry weight were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 0.87 g for a period of 11 weeks. The dietary DHA:AA ratio ranged from 62 to 0.2. Incorporation of AA into liver phospholipids increased with increasing dietary AA input. Phospholipids from fish fed diets containing 0.02, 0.06 and 0.11% of dry weight as AA generally contained less AA compared to fish fed fish oil while those fed diets containing 0.35 and 0.78% of dry weight as AA had higher AA levels in their phospholipids. The highest levels of AA were found in PI but the greatest percentage increase in AA incorporation was in PE and PC. Brain phospholipid fatty acid compositions were less altered by dietary treatment than those of liver but DHA content of PC and PE in brain was substantially lower in fish fed 0.93% pure DHA compared to those fed fish oil. This suggests that dietary DHA must exceed 1% of dry weight to satisfy the requirements of the developing neural system in juvenile turbot. In both tissues, (20:5n-3) concentration was inversely related to both dietary and tissue PI AA concentration. Similar dietary induced changes in AA, EPA and DHA concentrations occurred in the phospholipids of heart, gill and kidney. PGE₂ and 6-ketoPGF₁ were measured in homogenates of heart, brain, gill and kidney. In general, fish fed the lowest dietary AA levels had reduced levels of prostaglandins in their tissue homogenates while those fed the highest level of AA had increased prostaglandin levels, compared to fish fed fish oil. In brains, the PGE₂ concentration was only significantly increased in fish fed the highest dietary AA.Abbreviations AA arachidonic acid - DHA docosahexaenoic acid - EFA essential fatty acid - EPA eicosapentaenoic acid - HPTLC high performance thin-layer chromatography - HUFA highly unsaturated fatty acid - PC phosphatidylcholine - PE phosphatidylethanolamine - PGE prostaglandin E - PGE prostaglandin E - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid - TLC thin-layer chromatography  相似文献   

Incorporation and metabolism of14C-labelled polyunsaturated fatty acids in wild-caught juveniles of golden grey mullet,Liza aurata,in vivo     

Gabriel Mourente  Douglas R. Tocher 《Fish physiology and biochemistry》1993,12(2):119-130

The incorporation, and the capacity for desaturation and elongation in vivo, of intraperitoneally-injected,¹⁴C-labelled n-3 and n-6 C₁₈ and C₂₀ polyunsaturated fatty acids (PUFA) were investigated in juvenile golden grey mullet,Liza aurata. The results indicate that juvenile mullet have only limited ability to convert C₁₈ polyunsaturated fatty acids to C₂₀ and C₂₂ highly unsaturated fatty acids (HUFA)in vivo. This suggests that juvenile golden grey mullet require the provision of preformed C_20/22 HUFA, such as eicosapentaenoic and docosahexaenoic acids, in the diet. The impairment in the desaturase/elongase pathway was similar to that found in turbot,Scophthalmus maximus, and gilthead sea bream,Sparus aurata, being primarily at the level of Δ5-desaturase. The data from the largely herbivorous golden grey mullet juveniles are consistent with the hypothesis that marine fish in general, irrespective of dietary habits, have limited capacity for the desaturation and elongation of C₁₈ PUFA. The defect in Δ5-desaturase activity combined with the consistent finding that arachidonic acid is selectively incorporated and retained in membrane phosphatidylinositol suggests that, like turbot and gilthead sea bream, golden grey mullet may also have a requirement for preformed arachidonic acid in the diet.  相似文献   

Essential fatty acid deficiency in freshwater fish: the effects of linoleic, α-linolenic, γ-linolenic and stearidonic acids on the metabolism of [1-14C]18:3n-3 in a carp cell culture model     

Douglas R. Tocher  James R. Dick 《Fish physiology and biochemistry》2000,22(1):67-75

The desaturation of [1-¹⁴C]18:3n-3 to 20:5n-3 and 22:6n-3 is enhanced in an essential fatty acid deficient cell line (EPC-EFAD) in comparison with the parent cell line (EPC) from carp. In the present study, the effects of competing, unlabeled C₁₈ polyunsaturated fatty acids (PUFA), linoleic (18:2n-6), -linolenic (18:3n-3), -linolenic (18:3n-6) and stearidonic (18:4n-3) acids, on the metabolism of [1-¹⁴C]18:3n-3 were investigated in EPC-EFAD cells in comparison with EPC cells. The incorporation of [1-¹⁴C]18:3n-3 in both cell lines was significantly reduced by competing C₁₈ PUFA, with the rank order being 18:4n-3>18:3n-3 = 18:2n-6>18:3n-6. In the absence of competing PUFA, radioactivity from [1-¹⁴C]18:3n-3 in EPC cells was predominantly recovered in phosphatidylethanolamine followed by phosphatidylcholine. This pattern was unaffected by competing n-6PUFA, but n-3PUFA reversed this pattern as did essential fatty acid deficiency in the presence of all competing PUFA. The altered lipid class distribution was most pronounced in cells supplemented with 18:4n-3. Competing C₁₈ PUFA significantly decreased the proportions of radioactivity recovered in 22:6n-3, pentaene and tetraene products, with the proportions of radioactivity recovered in 18:3n-3 and 20:3n-3 increased, in both cell lines. However, the inhibitory effect of competing C₁₈ PUFA on the desaturation of [1-¹⁴C]18:3n-3 was significantly greater in EPC-EFAD cells. The magnitude of the inhibitory effects of C₁₈ PUFA on [1-¹⁴C]18:3n-3 desaturation was dependent upon the specific fatty acid with the rank order being 18:4n-3>18:3n-3>18:2n-6, with 18:3n-6 having little inhibitory effect on the metabolism of [1-¹⁴C]18:3n-3 in EPC cells. The differential effects of the C₁₈ PUFA on [1-¹⁴C]18:3n-3 metabolism were consistent with mass competition in combination with increased desaturation activity in EPC-EFAD cells and the known substrate fatty acid specificities of desaturase enzymes. However, the mechanism underpinning the greater efficacy with which the unlabeled C₁₈PUFA competed with [1-¹⁴C]18:3n-3 in the desaturation pathway in EPC-EFAD cells was unclear.  相似文献   

Development and Evaluation of Diets for Crustacean Aquaculture   总被引：1，自引：0，他引：1  

Clark E.  Bordner  Louis R.  D'Abramo  Douglas E.  Conklin Nancy A.  Baum 《Journal of the World Aquaculture Society》1986,17(1-4):44-51

Effective purified and unrefined diets have been developed and evaluated for use in studying the nutrition of lobsters ( Homarus sp.). A 4-month growth experiment showed that the purified diets yielded weight increases nearly 80% of that achieved on a live food diet, with concomitant high survival rates. Lower-cost unrefined diets supported growth over half of that observed on live food diets. Supplementation of a purified diet with an astaxanthin concentrate derived from crayfish waste enhanced growth significantly, and all the diets tested promoted growth and survival with only 0.2% dietary cholesterol.
Growth and survival are the most useful criteria for evaluating crustacean diets, but other factors such as proximate analyses of feeds, physical characteristics such as pellet leaching rates, and measurable physiological effects can provide important supplemental information. Our analysis of some of these factors suggests that pellet integrity and resistance to leaching may not be directly related either to growth, or to levels of binder in the diets.  相似文献   

Comparison of methods for sampling populations of ghost shrimp, Trypaea australiensis (Decapoda: Thalassinidea: Callianassidae)     

Douglas Rotherham  Ronald J. West 《Fisheries Research》2003,60(2-3):585-591

Coring and pumping methods, commonly used to determine the abundance and population parameters of burrowing ghost shrimp, were assessed in three widely separated south-eastern Australian estuaries. First, a comparison of two sizes of coring tube (0.04 and 0.07 m²) revealed no significant differences in catches of the ghost shrimp Trypaea australiensis Dana, nor differences in precision. However, the smaller sized core was consistently more cost effective. Second, when sampling a 0.1 m² quadrat, it was found that 12 “pumps” of a suction pump produced significantly higher numbers of individuals at most sites than using either four, eight or 16 pumps. In a third set of experiments, the coring method was compared to the pumping method, in terms of sampling efficiency, abundance estimates and sex ratios of captured ghost shrimp. Pumping was found to be more efficient, catching significantly greater numbers of ghost shrimp per minute than the coring. In addition, pump catches displayed a more normal size distribution than catches from the core and included a wider range of sizes. Sex ratios of catches from coring was 1:1, while catches from pumping were significantly biased toward females (0.71:1). Since female-biased sex ratios are characteristic of many thalassinid populations, this latter result probably reflects actual sex ratios for T. australiensis and not method based size selectivity.  相似文献