This study was conducted to assess the herbicide savings and the cost efficiency of site-specific herbicide application strategies in comparison with other strategies based on uniform application of herbicides throughout the whole field. The specific situation considered was Sorghum halepense infested maize fields in Spain. The results from a theoretical economic model were contrasted with the information derived from a S. halepense survey conducted in 37 commercial maize fields distributed over three Spanish maize production areas. Seven application strategies were simulated: 1) no herbicide; 2) overall full-rate; 3) overall half-rate; 4) and 5) site-specific spraying infested cells with full- and half-rate, respectively; 6) and 7) site-specific spraying infested cells plus adjacent buffer areas with full- and half-rate, respectively. The simulation results showed that site-specific weed management was the most profitable strategy when S. halepense infested area ranged between 6.5 and 18.7%. This scenario was present in 22% of the surveyed fields. In fields with less than 6.5% infestation (a situation present in 51% of the surveyed fields), yield losses were slight and the most profitable strategy was using no herbicide. When the infested area ranged between 18.7 and 40.8% (19% of the surveyed fields), no significant differences were observed between the net benefits of the various strategies. Full rate herbicide applications throughout the entire field resulted in the highest net returns in fields with more than 40.8% weed infestation (8% of the surveyed fields). In these cases, the added costs of weed detection, mapping and site-specific herbicide application were not justified by the herbicide savings obtained. Likewise, herbicide savings obtained with the various strategies depended on the proportion of the field infested. Considering the high difference between site-specific treatments and uniform application of herbicides when the infested area ranged between 18.7 and 40.8%, and that no significant differences in net returns were observed in this range, site-specific treatments should be preferred. Adding a buffer area to the site-specific treatments does not seem a suitable strategy due to the considerable increases in costs and reductions in herbicide savings. 相似文献
Abstract In a lysimeter study it was found that moderate rates of ammonium nitrate increased utilization percentages in spring wheat, and the leaching was 10% or less of added N. Over-optimal rates reduced utilization percentages and increased leaching to almost 50% of the highest doses. Late split application of calcium nitrate increased the percentage of N in grain. Furthermore, leaching of N was not reduced, but occurred somewhat later in the fall and winter seasons. Leaching of Cl? was more rapid and that of SO42- was delayed relative to the leaching of NO3?. Rather large negative N balances were obtained, also after over-optimal application rates, and total N content of the soil was reduced. Compared with the N0 treatment, differences in soil N residues amounted to 15–25% of added N in seven years. Gaseous losses had apparently taken place both from the added N and from soil N according to the total-N analysis. 相似文献
Two series of field trials were performed at three sites in Schleswig-Holstein between 1981 and 1988 to inquire into the yield structure of European winter types of Vicia faba L. and to compare their yield potential with that of spring types. Due to low winter survival, 6 winter types could be evaluated only in 4 environments in dependence of 1–3 sowing times (series α: seed rate 30/m2) and 1 winter type in 5 environments in dependence of 3 sowing times and 3 seed rates (series β: seed rate 15, 30, 45/m2). Seed yield of winter type averaged 410 g/m2 (D.M.) surpassing spring types by about 14 %. Environments caused a considerable variation in yield (275–620 g/m2) and in each yield component of winter types, while sowing dates and seed rates hardly affected the components seeds/pod and seed weight, which displayed stable genotypic rank orders. Compensative forces among the components plants/m2, tillers/plant and pods/tiller, were established. Plant densities of less than 10/m2 in spring, generally led to seed yield below 350 g/m2. Variation between 15–30 plants/m2 due to environments, sowing times or seed rates were frequently not fully compensated by tillering of plants, but often variation of the thus formed yield potential was reduced by pod set of tillers resulting in 210–270 pods/m2. The direction of correlations of pods/tillers with tillers/plant and plants/m2 differed due to experimental conditions whereas negative correlations between pods/tiller and tillers/ m2 were generally evident. Tillering was significantly influenced by the sowing time, though the increase because of early sowing was often covered by compensative effects of different plant densities. A genotypic capability to produce reproductive tillers was demonstrated using an approach which considered different plant densities and compensative forces. Neither a genotypic capability of tillers to set pods nor direct effects of environments or sowing time on pod set were established. 相似文献
The primary aim of the study was to investigate whether post-ejection udder massage 1–2 weeks pp (post partum) had an effect on the amount of mammary tissue and milk production in the domestic sow.
The nursing behaviour of 35 primiparous LYL or YLY sows and their litters was followed on days 7 and 14 pp. The milk production was measured by the weigh–suckle–weigh method of the whole litter on days 11 and 18 pp. After weaning on day 28 pp, the sows were slaughtered and the mammary tissue excised and weighed.
No significant correlations were found between the duration of post-ejection udder massage and the subsequent milk production. LYL sows had more mammary tissue (P < 0.05) and their piglets spent more time performing post-ejection udder massage compared to the YLY sows (P < 0.01). Individual variation was found in the proportion of time that the sows were lying on either their right or left side. The weight of the mammary tissue from the left side was positively affected by the amount of udder massage (pre- and post-ejection massage) that the sows had received while lying on the right side relative to the amount that she had received while lying on the left side on day 7 pp (P < 0.01).
In conclusion, the intensity of udder massage influenced the amount of mammary tissue at slaughter. The genotype of the sow affected the expression of nursing behaviour and milk production. No connection was found between post-ejection udder massage and the measures of milk production 1–2 weeks pp. Finally, feeding during the last half of gestation affected the nursing behaviour. 相似文献
A model was developed to explain the influence of different local and regional factors on the prevalence of foot-pad dermatitis in broilers at the time of slaughter. Data from a recent two-year study of broiler foot-health in Sweden were used to construct the model. The model was based on regression analysis, using a Tobit model for censored data. This type of Tobit regression model has been used for several decades in econometrics and can also be found in the medical-scientific literature. It has, however, reportedly not been used in veterinary medicine although there appears to be several situations where it should be considered useful. Week of slaughter was significantly (p<0.001) associated with total foot-pad score, which decreased over time. The birds' age at slaughter was also significantly (p<0.01) associated with total foot-pad score. Five out of the 11 slaughterhouses included in the study were included as significant (p<0.01) variables in the final model. Three feed suppliers (p<0.05) and four regions (p<0.01) were also included as significant variables in the model. There were also significant (p<0.001) interactions between several of these factors (mainly, between the time variable and specific slaughterhouses, feed suppliers or regions, respectively).
The information gathered in this study regarding the influence of a number of risk factors for the development of foot-pad dermatitis and their reciprocal interactions will enable us to modify the Swedish broiler foot-health programme. 相似文献
The role of tree diversity and identity as determinants of soil animal community structure is little understood. In a mature deciduous forest dominated by beech we identified clusters of one, two and three tree species of beech, ash and lime allowing to investigate the role of tree species diversity and identity on the density and community structure of oribatid mites. To relate oribatid mite community structure to environmental factors we measured leaf litter input, fine root biomass, mass of organic layers, topsoil pH and C and N content. We expected oribatid mite density to increase with increasing tree diversity, but we expected the effects of tree species identity to override effects of tree diversity. Further, we hypothesized the density of oribatid mites to be reduced by the presence of beech but increased by the presence of lime and ash. As expected tree diversity little affected oribatid mite communities, whereas tree species identity strongly altered density and community structure of oribatid mites. However, in contrast to our expectations the density of oribatid mites was highest in presence of beech indicating that many oribatid mite species benefit from the presence of recalcitrant litter forming thick organic layers. Especially Oppioidea benefited from the presence of beech presumably due to an increased availability of food resources such as fungi and nematodes. Lower density of oribatid mites in monospecific clusters of lime and ash suggests that oribatid mites did not benefit from high quality litter of these species. Notably, large and strongly sclerotized oribatid mite species, such as Steganacarus magnus and Chamobates voigtsi, benefited from the presence of ash and lime. Presumably, these large species better resist harsh microclimatic conditions in shallow organic layers. 相似文献
The main aims of this article are to calculate the erosion rates from sediments accumulated in the check dams and to compare the results with those of other methodologies. 相似文献