Excessive nitrogen (N) application has been considered as one of the reasons for restricting yield increases in rice-wheat rotation system in the Yangtze River area. From 2007 to 2009, field experiments were conducted to evaluate the effects of optimized N management on grain yield, nitrogen use efficiency (NUE) and N surplus of winter wheat in Jianghan Plain (Hubei province, China). Results indicated that grain yield and crop N uptake of treatments with reducing fertilizer N (N135(2) for the first year and N120(3) for the second season) did not significantly reduce yield compared to farmers’ practice (FP). Under the same amount of N application, three-time splitting improved grain yield and enhanced NUE as compared with two-time splitting. The optimized N treatment of N135(2) and N120(3) was observed with higher NUE parameters, i.e. recovery efficiency (REN), agronomic efficiency (AEN) and partial factor productivity (PFPN). Positive correlation between SPAD value and leaf N concentration provided the effective tool to evaluate N status during the growth season. The optimized N rate and top dressing frequency could reduce the residual N retained in the 0–20 cm soil layer after harvest, which could reduce the possibility of soil N loss to the environment. This paper provides insights into N management strategy based on farmers’ practices, which could be regarded as a guideline to improve agricultural management for wheat growth season. 相似文献
A feeding trial with five crude protein levels (549, 513, 472, 445 and 399 g kg?1) was conducted to investigate the optimum protein level in diets of juvenile southern flounder (Paralichthys lethostigma). Budgets of nitrogen and energy were discussed. Fish (initial weight 32.9 ± 0.5 g fish?1, mean ± SD) were fed the experimental diets to satiation twice daily for 61 days. Protein levels affected specific growth rate in wet weight (SGRW) and protein (SGRP) significantly. SGRW and SGRP were highest at 512.5 g kg?1 protein level. SGRW was positively correlated to growth nitrogen (GN), growth energy (GE), nitrogen digestibility, energy digestibility, amount of digestible nitrogen and amount of digestible energy. Faecal nitrogen (FN) and faecal energy (FE) were affected significantly with trends contrary to SGRW. The nitrogen budget was described by the equation 100CN = 2.1FN + 34.4UN + 63.5GN (CN, nitrogen intake; UN, excretion nitrogen). The energy budget was 100IE = 4.04FE +3.32UE + 54.35GE + 38.30ME (IE, gross energy intake; UE, excretion energy; ME, metabolizable energy). The average proportion of GE and ME in assimilated energy (AE) was described by the equation 100AE = 58.65GE + 41.35ME. 相似文献
Abstract. Effects of stocking density on water quality and on the growth, survival and food conversion of Oreochromis niloticus (Linnaeus) were evaluated. Fingerlings of tilapia (average weight 40.25 ± 94 g) were stocked in six 3.75-m3 concrete tanks at 16, 32 and 42.6/m3 and reared for 164 days. A water flow rate of 1 l/min/kg fish biomass was maintained in all the tanks. The growth rate was inversely related to stocking density with mean weights of 337.25g, 327.0g and 323.5g at the low, medium and high densities respectively. At harvest, standing crop biomass averaged 5.36 kg, 10.44kg and 13.24kg for the three densities. The respective food conversion ratios (FCR) were 1.85, 1.88 and 1.95, while the survival rates were 99.2, 99.6 and 95.9%. However, the survival rate, growth rate and food conversion efficiencies were not significantly different at the three stocking densities. Water quality did not deteriorate in different tanks as the oxygen was continuously replenished and metabolites and waste products removed by the water flowing through the tanks. These data suggest that culture of tilapia at a density of 42.6/m3 and production of 13.24 kg/m3 in 164 days with a production of 18–20 kg/m3 in a growing season (April-October) of 210 days is possible using the drainage water in flow-through water systems. 相似文献
Diseases in shrimp farms in the Mekong Delta of Vietnam cause significant crop losses and are therefore of great concern to producers. Once a pond becomes infected, it is difficult to prevent spread of the disease to nearby shrimp farming areas. Thus, predicting the occurrence of disease is an essential part of reducing the risk for shrimp farmers. In this study, we applied an integrated geographic information system and machine learning system to predict three serious diseases of shrimp, namely, acute hepatopancreatic necrosis, white spot syndrome disease, and Enterocytozoon hepatopenaei infection, based on data collected from shrimp farms in the Tra Vinh, Bac Lieu, Soc Trang, and Ca Mau provinces of Vietnam. We first constructed a map showing the distribution of these diseases using the locations of affected farms, and then we conducted spatial analysis to acquire the geographical features of the affected locations. This latter information was combined with environmental factors and clinical signs to form the set of independent variables affecting the outbreak of diseases. The neural network model outperformed the logistic regression, random forest, and gradient boosting methods in terms of predicting infection to estimate the probability of disease occurrence in farmed areas. Acute hepatopancreatic necrosis disease infected farms downstream of the Co Chien and Hau Rivers of Tra Vinh and west of Ca Mau. Enterocytozoon hepatopenaei infection is distributed in Soc Trang Province, while white spot syndrome virus has spread to the coastal districts of Soc Trang and Bac Lieu Provinces, where it is highly associated to water from a complex canal system.
The formation of mycorrhiza on Pinus tabulaeformis (Pt) seedlings by ectomycorrhizal fungi (ECMF), the protective effect of the ECMF on damping‐off caused by Rhizoctonia solani and the expression of pathogenesis‐related proteins (PR‐proteins) induced by Amanita vaginata and/or R. solani in Pt seedlings were investigated. The results indicated that: (i) among the 10 ECMF tested, five species (Gomphidius viscidus, Suillus laricinus, Suillus tomentosus, A. vaginata and Basidiomycetes no. 058) formed mycorrhiza with Pt seedlings. There was a positive correlation between mycorrhizal colonization levels and protective effects (r =0.9207). Among the five species, A. vaginata had the highest colonization level and the best protective effect against damping‐off; however, G. viscidus had no protective effect even though it had a high mycorrhization level. (ii) Chitinases, β‐1,3‐glucanases and PR‐proteins in the seedlings were not induced by A. vaginata colonization, but were induced when A. vaginata‐mycorrhizal seedlings were attacked by R. solani. It is possible that chitinases, β‐1,3‐glucanases and 108, 97, 78, 44, 37 and 14‐kDa PR‐proteins induced both by A. vaginata and R. solani protect Pt seedlings from R. solani infection. 相似文献
Natural occurrence of mosaic disease was observed on basil (Ocimum sanctum L.) in Aligarh, U. P., India, during 2008. The disease could be transmitted by sap inoculations from naturally infected O. sanctum to O. sanctum and some test plant species. Cucumber mosaic virus (CMV) was detected by RT-PCR using coat protein gene specific primers of CMV (Acc. AM180922 & AM180923), which resulted in
the expected size ~650 bp amplicon in infected samples. The amplicon was cloned, sequenced and data were deposited in GenBank
Acc. EU600216. The sequence data analysis revealed 97–99% identities at both nucleotide and amino acid levels with the CMV
strains of subgroup II reported worldwide. Based on the high sequence identities and close phylogenetic relationships with
CMV subgroup II strains, the virus under study has been identified as a new isolate of CMV subgroup II and designated as CMV-Basil. 相似文献
Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to examine the chemical emissions from the glued wood
samples at elevated temperatures (150, 200, 250, 300, 350, 400, 450, and 500°C). Two wood species, Douglas-fir (Pseudotsuga menziesii) and southern pine (Pinus palustris), one structural adhesive, phenol–resorcinol–formaldehyde (PRF), PRF-bonded Douglas-fir, and PRF-bonded southern pine were
evaluated. The volatile compounds with a mass range of 35–300 m/z emitted from the pyrolysis samples were separated by gas
chromatography (GC) and identified by mass spectrometry (MS). The results indicated that compared to neat wood and resin film
samples, several additional pyrolysis products were observed for the PRF-bonded wood samples including (1) acetaldehyde and
butanedial for PRF-bonded Douglas-fir and (2) acetaldehyde, furfural, 2-furanmethanol, butanedial, 2,3-butanedione, cyclopropyl
carbinol, 1,2-benzenediol, and 1-(acetyloxy)-2-propanone for PRF-bonded southern pine. These additional compounds were possibly
associated with the interaction between wood and PRF resin. The results also indicated that bonded wood products would be
less thermally stable than those of neat wood and PRF resin samples. 相似文献
To examine the sensitivity of environmental systems to climatic variability and change, integrated model systems for climate impact assessment are being developed for New Zealand (CLIMPACTS) and Bangladesh (BDCLIM). Features common to both model systems include a global climate model, regional modules for generating climate scenarios, and models for biophysical impact analyses. For CLIMPACTS, modified ecosystem models for horticultural crops, arable crops, and pasture production are being incorporated. For BDCLIM, the emphasis is on analysis ofpossible changes in agroclimatic zones and hydrology, including the risks of floods and droughts. The initial emphasis of both systems is on nationwide spatial analyses, using simplified models as much as possible. The development of integrated model systems supports the needs of the respective countries in assessing scientific uncertainties, evaluating vulnerabilities, and identifying adaptation options as a basis for international reporting requirements under the U.N. Framework Convention on Climate Change and for policy and planning at national and regional levels. The major advantage of such integrated model systems is that they can readily be updated as the science of climate change advances, thus providing an evolving tool for future reassessments of climate impacts. 相似文献
Agricultural landscapes are mosaics of different land uses. Their vast extent throughout the world means that they have a key role in the conservation of biodiversity. To provide a sound basis for management, it is important to recognise the emergent properties of land mosaics and understand how they influence components of biodiversity. In most studies in agricultural landscapes, inference is restricted to single sites or patches because this is the unit used for sampling and analysis. For mosaic-level inference, sampling must encompass multiple land uses and elements within a mosaic, be aggregated to represent the ‘whole’ mosaic, and be replicated across multiple mosaics. This paper reviews studies in which land mosaics are the unit of replication, to identify the influence on biota of three categories of emergent properties of mosaic structure: the extent of habitat, composition of the mosaic and spatial configuration of elements. The extent of habitat is usually a dominant influence on the occurrence of single species or the richness of assemblages defined by habitat type (e.g., forest birds). The composition of the mosaic, based on the proportions of elements present, strongly influences the species composition of faunal assemblages. Heterogeneity or diversity of elements is often positively correlated with the richness of taxonomic assemblages. In studies that separate the independent effects of emergent properties, spatial configuration generally exerts less influence on biota than extent or composition. A fourth property, the geographic position or environmental variation among land mosaics, also significantly affects the status of the fauna in many studies. Temporal persistence of species and turnover in assemblages in agricultural landscapes are also influenced by the structure of the land mosaic, but there are few long-term data sets that allow comparison of temporal changes with mosaic properties. There is great scope for further investigation of the properties of mosaics and the mechanisms by which they affect the conservation of biodiversity. This includes studies of responses from a wider range of biota (in addition to birds), investigation of spatial scale effects on faunal responses, temporal responses of the fauna to change in mosaic structure (and potential time-lags in response), and the effects of variation in mosaic structure on population demography and ecological processes. 相似文献
The effects of water vapor and CO on the photooxidation of propylene in the presence of NOx, were investigated. The presence of up to 11 000 ppm of water vapor had no significant effect on either the consumption of hydrocarbon and NO, or the formation of N02 and 03. A simplified mechanism for the phooxidation of propylene accounts for the observation by showing that the concentration of the major reactive radical-the OH radical-is not affected by the presence of HN02 formed initially as a result of the presence of water. Carbon monoxide at up to 200 ppm accentuated all symptoms of smog in the propylene-nitrogen oxide system. However, the effect caused by CO is much less than that caused by small changes in initial N02 concentrations. The magnitude of the accentuation does not justify control of CO solely to alleviate the symptoms of photochemical smog. 相似文献