Temporal changes of resource use,soil fertility and economic situation in upland Northwest Vietnam

Agricultural land in lowland Vietnam is scarce due to population growth. Hence, cultivation is increasingly practised on the steep upland slopes. Factors affecting resource use, soil fertility and household economics were studied in six villages of the Black Thai ethnic group in northwest Vietnam. Farmers were interviewed about their individual household situation. Yield development of major crops and cropping patterns in upland cultivation over the last 50 years were recorded in group discussions. In addition, soil fertility was analysed on different land‐use units. Formerly predominant upland rice changed to maize and cassava production at present. Decreasing soil fertility and a shift from subsistence to market‐oriented production, facilitated by new maize varieties and better access to markets are major causes. The Black Thai farmers economy has improved in recent years. The decline in soil fertility is concealed by higher maize yields from new varieties, and soil fertility conservation ranks low among farmers' priorities. The improved economy of the individual households might be of short duration if farmers cannot be sensitized to new resource management options. These have to be developed in line with farmers' priorities and the fragile environment of Vietnam's uplands. Copyright © 2002 John Wiley & Sons, Ltd.     

中国彭州市和越南东安地区蔬菜生产的肥料使用和评价

本文详细阐述了中国和越南4个村蔬菜生产中的肥料施用情况,概述了施用肥料的种类、施用时间和施用数量。评价了影响肥料施用的因素,比较了施肥量和蔬菜从土壤中带出的养分量。在研究区域,农户施用了50多种肥料,施氮量间于0～700kg／hm^2。肥料施用时间因蔬菜种类和地区不同而不同。氮的施用量主要受作物种类影响。大部分中国蔬菜的氮、磷施用量过大,而钾肥施用量不足;相对而言,越南蔬菜的局部养分平衡比中国的情况好一些。因此,局部的养分平衡显示了不同蔬菜种类、不同季节和不周村社的养分投入量和养分输出量有很大区别。     

Responses in residual feed intake in lines of Large White pigs selected for growth rate on restricted feeding (measured on ad libitum individual feeding)

Residual feed intake (RFI) represents the deviation of the actual ad libitum food consumption of each animal from that predicted from combination of growth rate, backfat and metabolic body weight measurements. After 4 years of divergent selection of pigs in lines for either high or low postweaning growth rate on restricted feeding, the high line exhibited a significant reduction in RFI relative to the low line. This indicated, to some extents, a lower energy requirement for maintenance in the high than in the low line, possibly because of reduced physical activity of the animals. Estimates of genetical parameters showed that RFI was moderately heritable and those genetic correlations of RFI with carcass backfat and food conversion ratio were moderate to highly positive.     

Prevalence of cpb2, encoding beta2 toxin,in Clostridium perfringens field isolates: correlation of genotype with phenotype

Beta2 toxin, encoded by the cpb2 gene, has been implicated in the pathogenesis of porcine, equine and bovine enteritis by type A Clostridium perfringens. By incorporating primers to cpb2 into a multiplex genotyping PCR, we screened 3270 field isolates of C. perfringens. Of these, 37.2% were PCR positive for the cpb2 gene. The majority of isolates from cases of porcine enteritis were positive for cpb2 (>85%), and this was even more true for C. perfringens isolated from cases of porcine neonatal enteritis (91.8%). In contrast, isolates from normal pigs only contained cpb2 in 11.1% of cases. The correlation between enteritis in other animal species and the presence of cpb2 was not so strong. cpb2 was found in 21.4% of C. perfringens isolates from cattle with enteritis, and in 47.3% of isolates from calves with enteritis or abomastitis. The prevalence of cpb2 varied with genotype, with type A isolates being positive for this gene in 35.1% of cases. Furthermore, enterotoxigenic type D or type E strains almost always carried cpb2. We cloned a 6xHIS-tagged beta2 (HIS-beta2) and used this protein to raise antiserum against beta2. Culture supernatants from 68 cpb2-positive and 13 cpb2-negative strains were tested for the presence of beta2 by Western blotting. In cpb2-positive isolates of porcine origin, beta2 was almost always detected (96.9%). However, in cpb2-positive isolates from other animal species, only 50.0% expressed beta2 protein. The high rate of cpb2-positivity among strains from neonatal pigs with enteritis and the high correlation of genotype with phenotype, supports the contention that beta2 toxin plays a role in the pathogenesis of these infections. However, it may be important to consider the use of an additional method for the detection of beta2 toxin in non-porcine cpb2-positive isolates when making claims about the role of beta2 in enteritis in non-porcine species.     

The epidemiology of nematode and fluke infections in cattle in the Red River Delta in Vietnam

Over a period of 13 months, faecal samples were collected monthly from approximately 45 cattle over 3 months of age. Additionally, 74 calves of 1-2 months were sampled to determine the presence of Toxocara vitulorum eggs. Individual egg counts and infective strongyle larvae from pooled faecal samples were examined. Post-mortem worm counts were carried out on six groups of tracer calves (n=12) that had been kept for 4 weeks on pasture in and around the village studied. The following helminths were identified: T. vitulorum, Cooperia punctata, C. pectinata, C. oncophora, Oesophagostomum radiatum, Trichostrongylus axei, T. colubriformis, Haemonchus spp., Fasciola spp. and Paramphistomum spp. In 8% of the samples collected from young calves, individual egg counts for T. vitulorum were found indicative for pathogenic worm burdens. Strongyle egg counts and worm counts indicated that transmission is low without a distinct seasonality. In animals of 3-9 months old, a strongyle egg count peak can be demonstrated which at a higher age steadily and significantly decreased. In faecal cultures Cooperia spp. were most prominent in all age groups throughout the year with the exception of the period September-November when Haemonchus spp. and Oesophagostomum spp. were most prevalent. Fasciola spp. eggs were found in 22% of the collected faecal samples and the egg counts were low indicating that the intensity of Fasciola spp. infection is mild. Based on the present data, regular anthelmintic treatments seem not to be justified, except for a single treatment at the age of 2 weeks against toxocariosis.     

Passive protection of dogs against clinical disease due to Canine parvovirus-2 by specific antibody from chicken egg yolk

The protective effect of immunoglobulins derived from chicken egg yolk (IgY) against infection by Canine parvovirus 2 (CPV-2) was evaluated in 10 beagle dogs orally challenged with a strain of the virus. The 2-mo-old dogs were divided into 3 groups and treated with powders containing CPV-2 IgY or normal egg yolk for 7 d after the challenge. The 4 dogs receiving normal egg yolk (control group) demonstrated mild symptoms typical of CPV-2 infection, such as vomiting, diarrhea, and weight loss. No symptoms were observed by 16 d after challenge in the 3 dogs receiving 2 g of IgY powder. Of the 3 dogs receiving 0.5 g of IgY powder, 2 had clinical CPV-2 disease; however, the manifestations were less severe than in the control group. Furthermore, the IgY-treated groups had significantly greater weight gain and shorter duration of virus shedding than the control group. These results indicate that IgY is useful in protecting dogs from CPV-2-induced clinical disease.     

Responses in carcass lean pH at 24 hours post-mortem in lines of Large White pigs selected for growth rate on a fixed ration over a set time

A restricted maximum likelihood analysis applied to an animal model showed no significant differences (P > 0.05) in pH value of the longissimus dorsi measured at 24 h post-mortem (pH24) between high and low lines of Large White pigs selected over 4 years for post-weaning growth rate on restricted feeding. Genetic and phenotypic correlations between pH24 and production and carcass traits were estimated using all performance testing records combined with the pH24 measurements (5.05–7.02) on slaughtered animals. The estimate of heritability for pH24 was moderate (0.29 ± 0.18). Genetic correlations between pH24 and production or carcass composition traits, except for ultrasonic backfat (UBF), were not significantly different from zero. UBF had a moderate, positive genetic correlation with pH24 (0.24 ± 0.33). These estimates of genetic correlations affirmed that selection for increased growth rate on restricted feeding is likely to result in limited changes in pH24 and pork quality since the selection does not put a high emphasis on reduced fatness.     

Quality and decomposition of black locust (Robinia pseudoacacia) and alfalfa (Medicago sativa) mulch for temperate alley cropping systems

Black locust and alfalfa mulch quality were characterized over a 9-week period of decomposition. Both mulch materials were harvested with a forage harvester. The black locust material was harvested from trees annually coppiced for four years, the alfalfa from a preflorescent second cutting. Two identical, adjacent experiments were conducted, one on each mulch source. A randomized complete block design was used with four replications for this single factor experiment. Fifty grams fresh weight of both mulch types were placed in litter bags, made of 98% shade cloth, a woven plastic with holes approximately 1×0.5 mm. The treatments included two placements of the mulch material, surface and buried. Sampling took place on weeks 0, 1, 3, 6, and 9.The incorporation of mulch materials appears to accelerate dry weight loss. From an initial dry weight of 44.25 g, the buried black locust mulch averaged 4.58 g, while the surface mulch averaged 7.41 g by week 6. The alfalfa mulch initially weighed 40.99g, with buried mulch averaging 1.75 g and surface mulch averaging 4.08 g by week 9.Carbon concentration of alfalfa mulch increased with time in both mulch placements from 43.6% to 57.6% and 51.8% in surface and buried mulch, respectively. Black locust, with an initial carbon concentration of 46.9% increased to 55.9% for the buried mulch and to 53.89% in surface mulch. Nitrogen concentrations increased as well in buried mulch. Lignin concentrations increased dramatically over time for both species of mulch. Black locust lignin concentrations rose from 13.11% to 51.0% (buried) and 32.9% (surface); alfalfa mulch lignin concentrations rose from 6.67% to 31.4% (buried) and 47.7% (surface).     

Evidence of Long-Range Transport of Pollutants from the Size-Fractionated Ionic Composition of Aerosols in the Jeju Island of Korea

The ionic composition of total suspended particulate (TSP) and fine (PM_2.5) fractions was investigated from an 1,100 site in the middle of Mt. Halla in Jeju Island, Korea from March to November 2006. The sum concentrations of cation and anion species in TSP fraction were 205 ± 170 and 183 ± 164 neq m^?3, respectively, while those for PM_2.5 as 118 ± 129 and 88.5 ± 89.3 neq m^?3, respectively. In TSP, the concentration of the major ions changed in the order of SO₄ ^2? > NH₄ ⁺ > Ca²⁺ > Na⁺ > NO₃ ^? > Mg²⁺ > K⁺ > Cl^?, while its PM_2.5 counterpart as NH₄ ⁺ > SO₄ ^2? > Ca²⁺ > NO₃ ^? > Na⁺ > Mg²⁺ > K⁺ > Cl^?. Inspection of the temporal variabilities of ionic components indicated that most ions peaked in spring or fall months. The back trajectory analysis showed that the atmospheric composition of the major ionic species was affected fairly sensitively by long-range transport from China under the favorable meteorological conditions. In contrast, the lowest ionic concentration levels were seen most abundantly, when air masses passed from South Sea. Hence, the analysis of ionic concentration data suggests that their distributions are controlled by the combined effects of various source processes including the most prominent Chinese origin and the meteorological condition favorable for such transport.     

Phosphorus Retention and Release Characteristics of Sewage-Impacted Wetland Sediments

Sediment deposited in traps positioned along a sewage-impacted wetland receiving phosphorus (P)-retaining reactants from natural wetland water was fractionated into different particle sizes, and the amount of P retained in these particle sizes was investigated. Subsamples of the sediments collected from different sites along the wetland system were also equilibrated with water at different water:sediment ratios and equilibration periods to investigate the extent of P released from these sediments under aerobic and anaerobic conditions. Results obtained showed that most of P deposited in sediments is in fine fractions (<16 µm), particularly in sediments collected from confluence sites where water inflow from the natural wetland provides P-retaining reactants and from sites immediately below these confluence sites (postconfluence sites). The extent of P release from sediments depended on the aerobic-anaerobic conditions of the sediments, equilibration period, water:sediment ratio and the position of sites within the wetland. The rate of P released from sediments associated with an increase in equilibration period tended to be higher under aerobic than anaerobic conditions. Water:sediment ratio was found to be a more important factor in controlling the release of P from sediments under anaerobic than aerobic conditions. The amount of P released from the confluence and postconfluence sites was higher than that from other sites over a range of equilibration periods and water:sediment ratios under aerobic and anaerobic conditions.