The mineralization/immobilization of nutrients from the crop residues is correlated with the quality of the plant material and carbon compartments in the recalcitrant and labile soil fractions. The objective of this study was to correlate the quality and quantity of crop residues incubated in the soil with carbon compartments and CO2-C emission, using multivariate analysis.
Materials and methods
The experiment was conducted in factorial 4?+?2?+?5 with three replicates, referring to three types of residues (control, sugarcane, Brachiaria, and soybean), and two contributions of the crop residues in constant rate, CR (10 Mg ha?1 residue), and agronomic rate, AR (20, 8, and 5 Mg ha?1 residue, respectively, for sugarcane, soybean, and Brachiaria), evaluated five times (1, 3, 6, 12, and 48 days after incubation). At each time, we determined the CO2-C emission, nitrogen and organic carbon in the soil, and the residues. In addition, the microbial biomass and water-soluble, labile, and humic substance carbons fractionated into fulvic acids, humic acids and humin were quantified.
Results and discussion
Higher CO2-C emissions occurred in the soil with added residue ranging from 0.5 to 1.1 g CO2-C m?2 h?1 in the first 6 days of incubation, and there was a positive correlation with the less labile organic soil fractions as well as residue type. In the final period, after 12 days of soil incubation, there was a higher relation of CO2-C emission with carbon humin. The sugarcane and soybean residue (20 Mg ha?1) promoted higher CO2-C emission and the reduction of carbon residue. The addition of residue contributed to an 82.32 % increase in the emission of CO2-C, being more significant in the residue with higher nitrogen availability.
Conclusions
This study shows that the quality and quantity of residue added to soil affects the carbon sequestration and CO2-C emission. In the first 6 days of incubation, there was a higher CO2-C emission ratio which correlates with the less stable soil carbon compartments as well as residue. In the final period of incubation, there is no effect of quality and quantity of residue added to soil on the CO2-C emission.
The breeding densities of many bird-species which nest in tree cavities are in some areas limited by shortage of sites. This is evident from circumstantial evidence in which the numbers of breeding pairs in different areas correlate with the numbers of local nest sites, or where changes in the numbers of nest sites resulting from natural processes or human action are followed by changes in the numbers of pairs. It is also shown experimentally, where nest site provision or removal has been followed by a corresponding change in breeding density.
When nest boxes were provided, they were often occupied in the same year, leading to an immediate rise in breeding density. This implied that surplus birds were available in the vicinity and able to take them up. In future years, pair numbers often increased further but eventually they levelled off. This implied that, at this higher level, other limiting factors came into play. Experiments on nest site provision thus provide examples of different factors acting successively to limit breeding density at different levels.
By constraining breeding density, shortage of nest sites not only prevents some birds from breeding, but must also limit the total numbers of breeders and non-breeders, because no population can increase beyond a certain point, when the production of young is limited. Once all available nest sites are occupied, reproduction is inevitably density-dependent with respect to the total population of breeders and non-breeders.
Because several bird species can use the same type of site, competition is frequent, and the numbers of dominant species can affect the numbers and distribution of others. In extreme situations, a species may be totally absent from areas where all suitable nest sites are occupied by dominant competitors. In less extreme situations, the numbers of a subordinate species may vary from year to year or from place to place in inverse relation to the numbers of a dominant species. Both these situations can be changed by the provision of extra sites.
In managed woods and modern tree plantations, most hole-nesting bird species are excluded or kept at extremely low levels by shortage of nest sites. This is a direct result of forestry practice, which usually entails removal of the old and dying trees that normally provide the sites. The problem can be rectified by allowing a number of old and dead trees to remain in managed forests, or (on a more local scale) by the provision of nest boxes. By appropriate design and positioning of the boxes, the most desired species can be favoured. 相似文献
A semiquantitative capillary column gas chromatographic method is described for the determination of diesel fuel contamination in various canned seafood products. The diesel contaminants are separated from the fish sample by steam distillation, with little carry-over of interfering intrinsic materials such as fish oils. The diesel fuel is extracted from the condensate with n-hexane, and the extract is analyzed on an SPB-1 fused silica capillary column. The efficiency of recovery of diesel fuel added to canned seafood at levels of 40-400 ppt ranged from 72 to 102%. With the additional step of concentrating the hexane extract, the sensitivity of this procedure may be increased at least 10-fold. This procedure can detect the differences among diesel fuel grades No. 1, 2, and 5, and variations within diesel grade No. 2, and thus may be useful in determining the type of petroleum contaminants present in various canned fish products. 相似文献
Summary Twenty-nine spring barley genotypes ranging from primitive landraces to modern cultivars were characterised for partial resistance to powdery mildew on detached leaves and in the field. Detached seedling and adult plant leaves were produced under spore-free glasshouse conditions and were assessed for infection frequency (IF) and then total mildew biomass using enzyme-linked immunosorbent assay (ELISA), and thereby biomass per colony (BMC), following controlled infection. Field plants were assessed visually for infection and for total mildew biomass using ELISA. Several genotypes were identified as having below average IF and BMC on both seedling and adult detached leaves and field scores of leaf area infected with mildew. IF at the seedling stage was highly correlated with IF at adult plant stage and with mildew biomass in the field. Adult plant IF was highly correlated with visual field scores. BMC data were often negatively correlated with other assessments. 相似文献
A range of mixtures including one set made from cultivars grown in the UK and one from cultivars grown in Poland, were included,
along with their component cultivars, in nine trials at Scottish Crop Research Institute, Dundee, UK or at the Experimental
Plant Breeding Station of the IHAR, Baków near Kluczbork, Poland, over five seasons. The effects of inoculum pressure, plot
size, fertiliser level and germplasm on mixture efficacy were investigated. In the four trials where inoculum pressure was
controlled, mixtures reduced infection more at lower inoculum pressures, but this did not translate into yield benefit. Smaller
plots increased mildew in monocultures but not mixtures. Fertiliser levels increased mildew levels but did not affect mixture
efficacy. There were large differences between both Polish and UK germplasm, and between Polish and UK trial sites, but the
performance of the mixtures compared with their respective monoculture components was similar within both germplasm groups
and trial sites. Mixtures reduced lodging and affected plant height and heading date. The advantages of mixtures for improving
yield, reducing fungicide applications and improving agronomic characteristics was demonstrated and there seems to be great
potential for their further improvement and exploitation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Summary Barley genotypes representing a wide range of resistance expressions and origins, from major resistance genes in modern cultivars to field resistances in landraces, were assessed for tolerance to disease under glasshouse and field conditions. A few genotypes were picked out as showing less yield loss than would be expected from the level of mildew infection. Genotypes showing more than the expected yield loss were also found. The potential use of tolerance as a breeding character is discussed. 相似文献
Parasitic zoonoses are common and widely distributed in the Southeast Asian region. However, the interactions between parasites, hosts and vectors are influenced by environmental, socio-cultural and livestock production changes that impact on the distribution, prevalence and severity of disease. In this review we provide an update on new knowledge in the context of ongoing changes for the food-borne pig associated zoonoses Taenia solium and Trichinella spp., the food-borne trematodes Opisthorchis viverrini and Clonorchis sinensis, the water-borne trematodes Schistosoma spp., the vector-borne zoonotic protozoa Plasmodium knowlesi and Leishmania spp. and the soil-borne zoonotic hookworm Ancylostoma ceylanicum. These various changes need to be considered when assessing or developing regional control programs or devising new research initiatives in a changing SE Asia. 相似文献
Peanut skins were fed at 15% of steer diets in metabolism and feedlot trials. Elevation of dietary protein using soybean meal or soybean meal plus urea and ammoniation of skins were evaluated as methods of overcoming detrimental performance and digestibility effects of tannins in peanut skins. Digestibility of dry matter, crude protein and energy were not different (P greater than .05) for steers fed a control diet with 11.4% crude protein with no skins compared with high-protein 15% peanut skin diets with soybean meal (15.5% crude protein) or soybean meal plus urea (16% crude protein). Dry matter, crude protein and energy digestibilities of control and of high-protein peanut skin diets were higher (P less than .05) compared with an 11.4% crude protein peanut skin diet and a 12.2% crude protein diet with ammoniated peanut skins. Ether extract digestibility was higher (P less than .05) for all peanut skin diets compared with the control. Nitrogen retention (g/d) was not different (P greater than .05) for control and high-protein peanut skin diets, and nitrogen retention on these diets was higher (P less than .05) compared with the lower protein and ammoniated peanut skin diets. Diets fed in the metabolism trial, except for the ammoniated peanut skin diet, were fed to 96 steers (345 kg initial wt) in a 109-d feedlot trial. Performance was lower (P less than .05) for steers fed the lower-protein peanut skin diet compared with other treatments through d 56; this diet was discontinued as a treatment on d 62.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
SUMMARY: Linear regression analysis was used to describe the decline in numbers of Culicoides brevitarsis Kieffer into winter with monthly maximum, average and minimum temperatures at the southern limits to its distribution in New South Wales. From this, low temperature thresholds were derived when C brevitarsis would be absent from the field. The low minimum threshold ± 2 SE (95% Confidence Interval) of 8.1 ± 0.3°C was used with historical temperature data to estimate the last month that the species should occur (March to June) and the mean number of months (2 to 6.5) below the threshold at 17 selected sites. Probability for survival during winter at these sites was estimated from years when the number of consecutive months below the threshold was ≤ 2 months. This varied from zero to 51% depending on the location of the site. Last occurrence was 0.7 months later on average and absolute probabilities for survival ranged from zero to 100% when the temperatures were increased by an arbitrary 2°C. 相似文献