Comparative assessment of several rainfall erosivity indices in Southern Nigeria

Soil erosion, measured in field runoff plots, was correlated with several rainfall erosivity indices. Erosion was measured on field plots established on a Typic Paleudult in southeastern Nigeria. Several erosivity indices were computed from a daily recording rain gauge sited in vicinity of the runoff plots. Erosivity indices computed included EI₃₀ (WISCHMEIER & SMITH 1978), KE>1 (HUDSON 1971) and AI_m (LAL 1976). In addition, several new indices were computed including E_kI_m and E_kI₃₀, where, the new kinetic energy (E_k) factor was computed using an empirical relation developed by KOWAL & KASSAM (1976) in northern Nigeria. Two new indices were slightly better correlated with soil erosion than the conventionally used indices.     

Perforation-mediated modified atmosphere packaging: Part I. Development of a mathematical model

A space-and-time dependent mathematical model describing perforation-mediated modified atmosphere packages was developed for respiring commodities. The model is based primarily on fundamental laws, with empirical relations used only when no other approach can be devised or when there is a significant advantage from using an empirical approach. The computational domain is divided into four subdomains: a part of the ambient storage environment; the perforation, allowing gas exchange between the package and the ambient; the commodity layer, inside the package; and the headspace above the commodity, but also contained in the package. The package walls are rigid and impermeable to gases but heat conducting. The commodity is treated as a homogenous porous medium with distributed sinks for oxygen consumption and distributed sources for carbon dioxide production due to commodity respiration. The commodity model also accounts for water vapour production due to transpiration and removal caused by possible condensation. The effects of commodity temperature and headspace gas composition on oxygen consumption and carbon dioxide production are accounted through a respiration model. The model permits the determination of the gas mixture velocity as the solution of Darcy's law in the commodity layer and the Navier–Stokes equations in the headspace, perforation, and surrounding ambient storage area. Transport of oxygen, carbon dioxide, water vapour and nitrogen is modelled based on Maxwell–Stefan equations coupled with the Navier–Stokes equations and Darcy's law. Solubility of carbon dioxide within the commodity has been included in the model. Commodity temperature and gas mixture temperature are modelled as solutions of the energy equation in the appropriate subdomains, coupled through transpiration, condensation, and convective heat transfer at the commodity surface.     

The analysis of spectroscopical data to map soil types and soil crusts of Mediterranean eroded soils

A study was carried out to investigate the potential use of imaging spectroscopy for mapping erosion hazard in Mediterranean areas. In the study area in southern France five soil types are recognized showing different vulnerability towards erosion. Samples were taken to the laboratory and exposed to artificial rainfall to stimulate crust formation. In the laboratory the spectroscopical behaviour of the soils with and without crusts was measured in the near and shortwave infrared in very narrow bands.Correspondence analysis was used to analyze the soil physical data and the soil spectra. This multivariate analysis method was useful to select spectral bands on which to focus to discriminate between the different soil types. Two important soil types having different vulnerability towards erosion, were discriminated by absorption features of iron and calcite. Crusting of the soils was not recognized by spectral absorption features, but generally crusts caused an increase of albedo of approximately 12%. This increase of albedo might be used to assess the presence of crusts.It was concluded that some main soil types can be discriminated by spectral absorption features and that imaging spectroscopy might have a good potential for surveying the hazard of physical soil degradation in Mediterranean areas.     

种子产业化的内涵及其理论基础(下)

(上接第 1期第 3页 )4　微观产业化的优势和局限性微观产业化的有利之处是 :(1)产业化内部各企业(包括龙头企业和被产业化的企业 )可以拥有稳定的生产资料供应来源和产品的需求市场 ;(2 )产业化内部各企业可以在相对稳定的价格下购入生产资料和销售产品 ,避免受市场价格波动的影响 ;(3)生产资料的质量可以相对地得到保障 ;(4)在产业化内部可以避免推销产品的各种费用 ,降低交易成本 ;(5 )有利于产业化内部各企业的设备投资 ;(6 )有利于产业化内部各企业的技术开发。然而 ,我们不能忽视微观产业化并不是一帖包治百病的万能药 ,作为在特定市场…     

Genetic analysis of Lolium. I. Identification of linkage groups and the establishment of a genetic map

A genetic map of Lolium has been produced using isozyme, restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) markers applied to a segregating family derived from an F₁ hybrid plant of L. perenne × L. multiflorum provenance, crossed on to a doubled haploid L. perenne. A total of 106 markers, out of a total of 160 polymorphic loci analysed, have been ascribed to seven linkage groups covering a map distance of 692cM, Two of these groups may be allocated to chromosomes 2 and 6 of the Lolium genome. The remaining unallocated markers, the majority of which showed severe segregation distortion, could be associated into small groups of two or three markers which showed no linkage with the main groups at a LOD of 2.8 or, if associated, could not be mapped in a satisfactory manner. This high incidence of disturbed segregations could be accounted for by the use of an interspecific hybrid between two species of differing genome size, with consequent cytological imbalance.     

The construction of a linkage map of Alstroemeria aurea by AFLP markers

An AFLP based linkage map has been generated for the ornamental crop species Alstroemeria aurea. In view of the large genome size of Alstroemeria (25,000 Mb) the number of selective nucleotides for AFLP amplification was increased to EcoRI+4/MseI+4 to generate fingerprints of moderate complexity. In addition, markers were generated with the enzyme combination Sse/Mse, where Sse8387I is an8-cutter, thereby reducing AFLP template complexity. Segregation of 374AFLP polymorphisms was recorded in the F₁ of an intraspecific A. aurea cross (A002 × A003). The map consisted of 8 A002 and 10A003 linkage groups with 122 and 214 markers covering 306.3 and605.6 cM, respectively. The two maps were integrated by using the21% of the AFLP markers that were heterozygous in both parents, and31% of the markers remained unlinked. Pollen color was assigned to linkage group A002-6. The enzyme combinations EcoRI+4/MseI+4 and Sse+2/MseI+3 generated 80 and 30 clear bands per lane with 16 and 9 polymorphic markers, respectively. Twenty percent of the EcoRI+4/MseI+4 primer combinations resulted in fingerprints that were disturbed by a few excessively thick bands (55 out of 288 primer combinations). We conclude that fingerprints and markers generated with the eight-cutter enzyme Sse8387I, in combination with+2/+3 selective nucleotides (Sse+2/MseI+3) are superior toEcoRI+4/MseI+4. This revised version was published online in August 2006 with corrections to the Cover Date.     

多熟种植——中国农业的中流砥柱

以高产、优质、高效、生态为目标的多熟制适合中国国情与需要,遍布南北的多熟种植是中国农业的中流砥柱,必须加以保护、支持与发展。集约化是中国多熟制的主要特征,持续化是多熟制的重要保证,要从中国实际出发,坚持走中国式的多熟农业集约化与持续化相结合的道路,半个多世纪中国农业实践和研究证明,通过艰苦努力达到这个目标是可能的,不能盲目跟着西方的模式或时兴口号走。中国多熟制的前途是和中国农业的前途紧紧捆绑在一起的,要坚持以多熟为主体的集约持续农业战略,积极推进传统多熟农艺现代化、科学化。     

Studying airflow and heat transfer characteristics of a horticultural produce packaging system using a 3-D CFD model. Part I: Model development and validation

A 3-D computational fluid dynamics (CFD) model of airflow and heat transfer processes within packed horticultural produce was developed. The model included explicit geometries of the product and package. Model results showed that airflow and temperature inside produce bulk were heterogeneous. The regions near the package vents showed relatively higher cooling air velocity and turbulence intensity. The coldest region was located behind the entrance vents. Pressure drops through entrance and exit vents were 51.1% and 45.2%, respectively. As the cooling air passed through the package vents and produce bulk, there was an increase in turbulence intensity. Validation of the model was conducted using experimental results. There was a good agreement between the predicted and measured results, average relative errors of predicted pressure drop and produce temperature were 13.80% and 16.27%, respectively.     

Application of a dendrogram seriation algorithm to extract pattern from plant breeding data

A dendrogram is often used to display the results from hierarchical clustering; however, the order of objects in a standard dendrogram is arbitrary and so similarity cannot be readily interpreted. An optimized dendrogram, a dendrogram produced by re-ordering the objects using a seriation method, has a customized ordering that reflects the similarity among objects with most similar objects located closest together. Hierarchical clustering has been applied to the analysis of data from plant breeding programs to identify the patterns in breeding populations and to study genotype by environment interactions. In this paper we demonstrate the advantage of an optimized dendrogram for interpretation of plant breeding data and, given this advantage, argue that an optimized dendrogram should be used as the default whenever hierarchical clustering is used.     

Mixing and flushing of tidal embayments in the western Dutch Wadden Sea part I: Distribution of salinity and calculation of mixing time scales

The distribution of salinity in the western Dutch Wadden Sea is described, mainly on the basis of surveys carried out during 1970 to 1974. Relations are discussed between the salinity distribution and relevant environmental factors such as: fresh water discharge, salinity of the North Sea, the tide, the windfield and the morphology of the area. Flushing time scales of 15 and 31 tidal periods were obtained for fresh water originating from the main sluicing gates near Den Oever and Kornwerderzand, respectively Stationary salinity distributions were used for the calculation of exchange coefficients between compartments of a box model of the area. By means of the box model a series of time scale relevant to the flushing of the area has been calculated and their areal distribution is shown. Distinction has been made between ages and transit times of water originating either from one of the two tidal inlets (sea water) or from one of the two sluicing gates (fresh water). Of the former, the ages in the basin (11.3 and 12.3 T) exceed the transit times (2.7 and 3.0 T) whereas the opposite is found for fresh water (ages 10.6 and 19.8 T, transit times 14.5 and 29.1 T). Turn-over times of the main tidal basins were also calculated, the result being 13.7 T for the Marsdiep basin and 9.0 T for the Vlie basin.     

Water and salt transport in the irrigated cracking clay soils of the Kachhi Plains,Pakistan: Part I. Vertical transport

Investigations with respect to the transport of water and salt in the irrigated cracking clay soils of the Kachhi Plains in Pakistan are reported. The leaching of salts under intermittently irrigated crops on deep fine-textured soils is insufficient. Hence, such crops can be grown only if deeper leaching under a wet crop is provided from time to time.The results of field observations and infiltration experiments indicate that more water transport and salt leaching occurs if the fine-textured topsoils are underlain by more permeable medium-textured subsoils at depths between 50 and 150 cm. This suggests that it is not the cracked topsoils but the uncracked subsoils that limit the water transport in deep fine-textured soils. The infiltration experiments show that swelling and the closing of cracks under water ponding is a slow process, lasting more than 1 month.     

Agglomeration and firm performance in times of economic turmoil: Evidence from Tunisian firm-level data

The paper analyzes the relationship between agglomeration economies (urbanization, specialization, and diversity) and firm-level performance during a period of deep economic downturn (2011–2018). We use data from the National Survey of Economic Activities for eight Tunisian manufacturing industries to explore which agglomeration externalities matter most for firm performance after the revolution. The analysis considers, in addition, the role played by selected firm-specific characteristics. The empirical results, based on a multilevel analysis approach, sanction the importance of firm-specific determinants of productivity and exporting. They also indicate that only specialization externalities have a positive and significant effect on firms' performance. The replicate results during a period of economic stability (1998–2004) show, however, that specialization and urbanization economies are both relevant predictors of firms' productivity and that more productive firms, in particular the smaller ones, are better able to benefit from agglomeration. This finding has not been confirmed for the post-revolutionary period.     

Temperature abuse timing affects the rate of quality deterioration of commercially packaged ready-to-eat baby spinach. Part I: Sensory analysis and selected quality attributes

Temperature abuse of fresh-cut products occurs routinely during transport and retail store display. However, the stage of product shelf life during temperature abuse and its impact on sensory attributes have not been studied. This study evaluated the effect of temperature abuse occurring immediately after processing and late in shelf life through measurements of sensory attributes, and membrane integrity of commercially packaged ready-to-eat baby spinach. The packaged products were received within 2 days of processing. Samples subject to early temperature abuse were immediately placed at 1, 4, 8, 12, 16 and 20 °C storage upon arrival, and those subject to late temperature abuse were stored at 1 °C for six days, and then transferred to 4, 8, 12, 16 and 20 °C storage. Package headspace gas composition, in-package visual appeal, purchase intent, product color, off-odor, decay, texture, overall quality, and tissue electrolyte leakage were evaluated every 1–2 day up to 16 day total. Results indicate that when the product temperature is maintained at 1–4 °C, the quality of commercially packaged baby spinach can be retained for up to 18 days post-processing. However, storage temperature of 8 °C or above, significantly (P < 0.001) shortened product shelf life as exhibited by accelerated tissue electrolyte leakage, product yellowing, decay and off-odor development. Most importantly, the product's shelf life stage significantly affected its response to temperature. Quality deterioration proceeded more rapidly when temperature abuse occurred in late as opposed to early shelf life stage.     

Varietal selection for perennial crops where data relate to multiple harvests from a series of field trials

Varietal selection for yield from a series of multi-environment trials can be regarded as a multi-trait selection problem in which the yields in different environments are synonymous with traits. As such an analysis of the data combined across environments should be conducted in order to form an index for selection. Analytical methods that include appropriate models for both the genetic variance structure (that is, the variances and covariances of genotype effects from different environments) and the residual variance structure (which typically comprises spatial covariance models for each trial) have been published previously. In the case of perennial crops, yields are often obtained from multiple harvests which implies that the data comprise short sequences of repeated measurements. Varietal performance in individual harvests is important for selection so that a combined analysis across both trials and harvests is required. The repeated measures nature of the data provides additional modelling challenges. In this paper we propose an approach for the analysis of multi-environment, multi-harvest data that accommodates the major sources of variation and correlation (including temporal). The approach is illustrated using two examples from sugarcane breeding programmes. The proposed models were found to provide a superior fit to the data and thence more accurate selection decisions than the common practice of conducting separate analyses of individual trials and harvests.     

Population genetic responses of wild forage species to grazing along a rainfall gradient in the Sahel: A study combining phenotypic and molecular analyses

Genetic diversity was studied in wild forage species subjected to grazing along a rainfall gradient in West Niger, within the Sahel with aim of identifying adapted genotypes, which could be used to reclaim degraded land. Two legumes (Alysicarpus ovalifolius and Zornia glochidiata) and two grasses (Brachiaria xantholeuca and Cenchrus biflorus) were selected to relate phenotypic adaptation to genetic diversity in response to grazing and rainfall. Populations of each species were sampled from both heavily grazed and ungrazed sites along a rainfall gradient, approximating 200 mm yr⁻¹ to 800 mm yr⁻¹ rainfall isohyets. The adaptative phenotypic expressions to aridity and grazing of the populations from each of the species were characterised by morphological measures performed on the plants sampled in the field. These analyses were then compared with the results from genetic analyses using the PCR-based techniques of amplified fragment length polymorphism (AFLP) and random amplified polymorphic DNA (RAPD). Analyses of molecular data using cluster analysis (UPGMA), principal co-ordinates analysis (PCO), Mantel tests and an Analysis of Molecular Variance (AMOVA), revealed genotypic distinction between populations subjected to both differing aridity and grazing. The majority of the total genotypic variation sampled in all species occurred among individuals within a population. The significant morphological differentiation found among populations subjected to varying grazing and aridity stresses, determined through linear regression analyses, did not correlate significantly with the genotypic differentiation, as revealed by Mantel tests. The results suggest that grazing does not cause a loss of genetic diversity in the wild forage species studied, although with increasing aridity the impact of grazing on the genetic diversity of populations may increase.R. Jamnadass and A. Muchugi Equal contribution to this work by both authors.