Aggregate stabilization in kaolinitic soils by low rates of anionic polyacrylamide     

W. P. Miller  R. L. Willis  G. J. Levy 《Soil Use and Management》1998,14(2):101-105

Abstract. The stability of aggregates can be improved by amending the soil with charged synthetic polymers. We have evaluated the effects of addition of low rates of anionic polyacrylamide (PAM) on the stability of aggregates from three predominately kaolinitic soils, and investigated whether the applied PAM penetrated into the aggregates or was adsorbed onto exterior surfaces only. Aggregates (6.3–9.5 mm) from the Ap horizons of a Cecil sandy loam and a Cecil loamy sand (Typic Kanhapludult) and from the Bt horizon of a Davidson clay (Rhodic Kandiudult) were treated with a high molecular weight(2 × 10⁷Da), negatively charged (20% hydrolysis) PAM at rates of 0, 10 or 20 kg/ha. The treated aggregate were dried and exposed to 20 mm of high kinetic energy (23.0 kJ/m³) simulated rain. Some of the PAM-treated Cecil loamy sand aggregates (5 or 10 kg/ha) were broken in half to expose untreated aggregate interiors to the rain. Percentage stable aggregates (weight/weight) in the PAM treatments ranged from 52 to 97%, vs. 20-32% in the control. PAM addition significantly increased the percentage of >4 mm sized aggregates compared with the untreated aggregates. PAM was more effective at stabilization in the light to medium textured Cecil soils than in the clayey Davidson. When internal surfaces of PAM treated aggregates were exposed, the percentage of stable aggregates exceeded the amount expected if the polymer was only adsorbed on to external surfaces. This suggested that some PAM had penetrated to some degree into aggregate interiors, thereby stabilizing both external and internal aggregates surfaces. Based on these results it is envisaged that use of PAM could be a viable alternative to the commonly used soil and water conservation practices (e.g. mulching, dyking, contour tillage).  相似文献   

Soil and weed management for enhancing arbuscular mycorrhiza colonization of wheat     

I. Brito  M. Carvalho  M. J. Goss 《Soil Use and Management》2013,29(4):540-546

Tillage and weed control are critical components of cropping systems that need to be combined such that crops benefit from reduced competition. However, weeds may also contribute to the biological diversity within the agro‐environment. This greenhouse study investigated whether common weeds of arable cropping systems were suitable host plants for arbuscular mycorrhizal fungi (AMF), allowing the development of extraradical mycelium (ERM) that can contribute to the early colonization of a following wheat crop, especially in the absence of soil disturbance. Weeds were allowed to grow for up to 2 months before being controlled by soil disturbance or herbicide application (glyphosate or paraquat). Pregerminated wheat seeds were then planted. Chemical control of the weeds prior to sowing enhanced the early arbuscular mycorrhiza (AM) colonization rate of wheat roots, whereas mechanical disturbance was less acceptable as a method of weed control for rapid AM colonization. The type of herbicide (contact or systemic) had no impact on colonization of the wheat crop. Enhanced AM colonization promoted early P acquisition and growth of the crop. Appropriate management of weeds emerging between two consecutive cropping seasons coupled with no‐till soil management could ensure a quick and efficient AM colonization of the following wheat plants.  相似文献   

Effects of Dietary Fiber on Growth and Gastric Emptying Time of the Freshwater Prawn Macrobrachiurn rosenbergii (De Man, 1879)     

Maria  del Carmen González-Peña Santo Z.  Gomes Gloria S.  Moreira 《Journal of the World Aquaculture Society》2002,33(4):441-447

Feeding experiments were conducted on large and small adult freshwater prawns Macrobrachium rosenbergii (36.96 ± 1.65 and 13.48 ± 1.65 g in weight) to determine the impact of dietary fiber on growth, digestion, and gastric emptying time. Fiber was incorporated as Q- cellulose into four semi-purified diets at calculated levels of 0, 5, 10 and 15% at the expense of starch and fed for an 8-wk period. The experiment was conducted in a closed, filtered, recirculating freshwater system. The results indicate that the specific growth rates, feed conversion ratios, and protein efficiency ratios improved as the levels of dietary fiber increased from 0.4% to 8%. Gastric emptying times increased as the level of inclusion of cellulose in the diets increased. It was concluded that diets containing up to 10% dietary fiber increases growth rates in adult prawn Macrobrachium rosenbergii by increasing nutrient residence time in the gastrointestinal tract, thereby increasing absorption.  相似文献   

Response of feral cats to vaccination at the time of neutering     

Fischer SM  Quest CM  Dubovi EJ  Davis RD  Tucker SJ  Friary JA  Crawford PC  Ricke TA  Levy JK 《Journal of the American Veterinary Medical Association》2007,230(1):52-58

OBJECTIVE: To determine whether administration of inactivated virus or modified-live virus (MLV) vaccines to feral cats at the time of neutering induces protective serum antiviral antibody titers. DESIGN: Prospective study. ANIMALS: 61 feral cats included in a trap-neuter-return program in Florida. PROCEDURES: Each cat received vaccines against feline panleukopenia virus (FPV), feline herpes virus (FHV), feline calicivirus (FCV), FeLV, and rabies virus (RV). Immediately on completion of surgery, vaccines that contained inactivated RV and FeLV antigens and either MLV or inactivated FPV, FHV, and FCV antigens were administered. Titers of antiviral antibodies (except those against FeLV) were assessed in serum samples obtained immediately prior to surgery and approximately 10 weeks later. RESULTS: Prior to vaccination, some of the cats had protective serum antibody titers against FPV (33%), FHV (21%), FCV (64%), and RV (3%). Following vaccination, the overall proportion of cats with protective serum antiviral antibody titers increased (FPV [90%], FHV [56%], FCV [93%], and RV [98%]). With the exception of the FHV vaccine, there were no differences in the proportions of cats protected with inactivated virus versus MLV vaccines. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that exposure to FPV, FHV, and FCV is common among feral cats and that a high proportion of cats are susceptible to RV infection. Feral cats appeared to have an excellent immune response following vaccination at the time of neutering. Incorporation of vaccination into trap-neuter-return programs is likely to protect the health of individual cats and possibly reduce the disease burden in the community.  相似文献   

Amending Soil with Sludge,Manure, Humic Acid,Orthophosphate and Phytic Acid: Effects on Infiltration,Runoff and Sediment Loss     

Amrakh I. Mamedov  Benayahu Bar‐Yosef  Irit Levkovich  Rivka Rosenberg  Avner Silber  Pinchas Fine  Guy J. Levy 《Land Degradation \u0026amp; Development》2016,27(6):1629-1639

Application of organic wastes to cultivated lands can replace mineral fertilizers but may also alter soil physical properties and enhance pollution potential. The objective of this study was to investigate the effects of biosolids [composted manure (MC) and activated sludge (AS)] and specific biosolid component [orthophosphate (OP), phytic acid (PA) and humic acid (HA)] application on soils differing in texture [loamy‐sand (Ramat‐HaKovesh, RH), loam (Gilat, GL) and clay (Bet‐Dagan, BD)], infiltration rate, runoff volume and soil sediment loss. The soils were packed in erosion boxes (400 × 200 × 40 mm) and subjected to six consecutive simulated rainstorms, each of 186 mm deionized water. The results showed that runoff volume and sediment loss from untreated soils increased with increasing clay contents. In treated soils, the response to AS application differed from the response to other amendments; in the BD clay and GL loam, it was the only amendment that caused a decrease in sediment removed by runoff. In the RH loamy‐sand, all amendments reduced the final infiltration rate, but only AS and HA increased the measured runoff. It is proposed that the difference in the response of the soils to the amendments is associated with the soil's ability to attenuate changes in the negative charge on the clay edges following the increase in the specific adsorption of charged anions, thus controlling clay swelling and maintaining aggregate integrity. The effects of amending soils with a source of organic matter in order to control runoff and soil erosion are not straight forward and depend on soil and amendment properties. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A shattering-resistant mutant of Papaver bracteatum Lindl.: characterisation and inheritance     

Arieh Levy 《Euphytica》1985,34(3):811-815

Summary Papaver bracteatum is a potential crop for the codeine industry. Seed shattering prevailing in the species is a major problem which reduces the seed yields. A spontaneous mutant with capsules having no pores of dehiscence was isolated in an experimental field. The seed yields of this shattering-resistant mutant are lower than in plants with normal capsules but the thebaine content of the capsules from the mutant is higher. The mutation is monogenic dominant; it can be used for breeding cultivars for dual purpose-thebaine and seeds.  相似文献   

Variations in pathogenicity patterns ofMycosphaerella graminicola withinTriticum spp. in Israel     

Z. Eyal  E. Levy 《Euphytica》1987,36(1):237-250

Summary Pathogenicity patterns of 42Mycosphaerella graminicola (Septoria tritici) isolates secured from the major wheat growing regions in Israel, were assessed on seedlings of 16 bread and durum wheats. The spring bread wheat cultivar Titan (CI12615), the winter bread wheats Bezostaya 1, Kavkaz, NE7060 and the durum wheats Nursit 163 and Zenati Bouteille, all exhibited a high level of resistance. Significant cultivar × isolate interactions were recorded for isolates from the different regions in relation to the response of the 16 cultivars organized in 6 reponse classes to the test isolate ISR8036. Number of genes for resistance in the 16 cultivars was estimated, based on the assumption of a gene-for-gene relationship. Twelve complementary genes were hypothesized in the 42M. graminicola isolates × 16 wheat cultivars matrix. There was considerable variation in virulence frequencies between regions and between locations within the same region. The overall frequency of Bezostaya-Kavkaz virulence was low throughout the country (5–7%). The frequency of designated hypothesized virulence genes VST OLAF, VST COLOTANA, VST IAS 20 in Israel, was high in most locations. The reported analytical approach enables the identification of virulence hot-spots and assists in designing breeding for resistance strategies.  相似文献   

Interaction of the mutant genes B,og c,hp and t in the coloring of tomato fruit     

Thiago Matos Andrade  Wilson Roberto Maluf  Celso Mattes de Oliveira  Luiz Antônio Augusto Gomes  Daniela Costa Santos  Regis de Castro Carvalho  Ranoel José de Sousa Gonçalves  Álvaro Carlos Gonçalves Neto 《Euphytica》2015,205(3):773-783

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Path analysis of genotype-environment interactions of potatoes exposed to increasing warm-climate constraints     

George C. C. Tai  David Levy  Warren K. Coleman 《Euphytica》1994,75(1-2):49-61

Summary Twenty potato cultivars were tested in replicated trials in three seasons. The weather gradually changed from relatively high humidity and cold air temperatures in February to dry and hot in July. Fresh and dry weights, sucrose, reducing sugar and starch contents were recorded on tubers sequentially harvested over four stages during the growing period of each of the three trials. The data were analyzed for genotype-environment interactions by a path regression model which is composed of a main effect and four multiplicative effects. The model fitted well to the observed data for all traits but reducing sugar. Results of dry tuber weight were used to calculate a heat susceptibility index for each of the cultivars. Four components of the index were identified based on the path model. Comparison of sizes of the components provided information on the degree of response to the environmental stress of each of the cultivars during successive stages of growth. High yielding and heat tolerant cultivars were identified based on the experimental results.  相似文献   

Potato germplasm development for warm climates: genetic enhancement of tolerance to heat stress     

Richard E. Veilleux  Margarita M. Paz  David Levy 《Euphytica》1997,98(1-2):83-92

Complex potato hybrids were derived through unilateral sexual polyploidization between Solanum tuberosum cv. Atlantic and 11 diploid hybrids that produced 2n pollen through co-orientation of second division spindles. The hybrids represented the following genomic compositions: TAPB, TAPC, and TAPM where T = S. tuberosum, A = S. andigena, P = S. phureja, B = S. berthaultii, C = S. chacoense, and M = S. microdontum. The B, C, and M components of the hybrids had been selected from heat tolerant accessions. The heat tolerance and agronomic performance of the hybrids were assessed under both controlled environments and field tests. The hybrids exhibited good tuberization potential (tuber number, tuber weight and percent plants producing tubers) under heat stress conditions in controlled environments. Under severe heat stress conditions in the field in Israel, many of the hybrids tuberized when Atlantic failed to produce any tubers at all. Under more moderate heat stress in Virginia, the complex hybrids exhibited total tuber yield not significantly different from Atlantic, although the tuber set per plant was greater. However, the complex hybrids were more tolerant to heat necrosis and hollow heart than Atlantic. Total glycoalkaloids in field-grown tubers did not exceed the acceptable limit for 13 of 26 selections examined. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献