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71.
72.
The Vertisols of the Purna Valley, which cover the districts of Amravati, Akola and Buldhana in the state of Maharashtra, India, lack any perceptible evidence of salt efflorescence on the soil surface which would indicate the presence of salt, but the drainage conditions are poor. The limited data available indicate that the adverse physical condition of the soils is due to their poor hydraulic conductivity (HC), which is impaired by sodium in the exchange complex. However, the factors and processes that are inherently related to the development of sodicity in these shrink-swell soils are not yet understood. In order to establish the cause-effect relationship, eight Vertisol pedons from methodically selected sites were studied morphometrically in the field, and for their sodicity-related physical and chemical properties in the laboratory. The soils are deep, calcareous, clayey and very dark greyish brown to dark brown in colour. Cracks extend up to the slickenside zones in soils of Pedons 1–3 in the northeastern area of the valley, while they cut through the slickenside zones in soils of Pedons 4–8 in the southwest. The slickenside faces were larger in the soils of the southwest than in those of the northeast. All these soils meet the specifications of the Vertisols order of soil taxonomy. Saturation extracts of the soils had very low electrical conductivity (ECe ⩽ 2 ds m−1). They ranged from moderately alkaline in the northeast, Pedons 1–3, to strongly alkaline in the southwest, pedons 4–8. In soils from the northeast the exchangeable sodium percentage (ESP) was less than 5 throughout the depth of the pedons, whereas in other soils it was up to 6 in the surface horizons and between 7 and 26 in the subsoil horizons; four of these soils qualified as sodic according to the criteria of the United States Salinity Laboratory. The inherently low hydraulic conductivity was due to the dispersion of clay particles caused by a high percentage of exchangeable magnesium (EMP) in the highly smectitic soils, and also to a slight increase in ESP (⩾5). The results of this study suggest that ESP 5 should be used as the lower limit for sodic subgroups of Vertisols, rather than ESP 15 as given in Keys to Soil Taxonomy (Soil Survey Staff, 1994). This is because there are severe limitations to the use of such soils owing to the development of adverse physical conditions even at such a low ESP. The authors emphasize the need to keep this fact in mind during future land resource management programmes on the soils of this valley as well as on similar soils occurring elsewhere. The development of sodicity in the soils of the southwestern part of the valley has been attributed to the semi-arid climatic conditions that have induced the pedogenetic process of depletion of calcium ions from the soil solution in the form of calcium carbonate, thereby resulting in an increase of both the sodium adsorption ratio (SAR) and the ESP with pedon depth. This chemical degradation, which affects the sodicity of Vertisols, appears to be a basic process that needs to be recognised in the future along with those already described as natural processes of soil degradation.  相似文献   
73.
The effects of total electrolyte concentrations of the equilibrium solutions (t.e.c.) on Ca2+-Na+ exchange equilibria in two soil samples (high and low in organic matter, clay content and CEC) were studied. Homoionic (Na+-saturated) soil samples were equilibrated with solutions having a large range in sodium adsorption ratio (SAR) at 25, 50, 75 and 100 meq. 1-1 t.e.c. The exchange equilibria data were analysed, using a thermodynamic approach and the selectivity coefficients of Gapon (1933), Vanselow (1932) and Krishnamoorthy et al. (1948) (KG, KV and KKDO). At a given proportion of Ca2+: Na+ in the equilibrium solution, the development of the exchangeable sodium percentage (ESP) in both soil samples increased with the increase in t.e.c. At a given SAR, the effect of t.e.c. on the development of ESP was less on a soil sample with high organic matter (O.M.), clay content and cation exchange capacity (CEC) than on a soil sample with low O.M., clay content and CEC. The values of exchange selectivity coefficients decreased with the increase in t.e.c, and did not remain constant throughout the exchange isotherm for any of the t.e.c. tried.  相似文献   
74.
Plant breeders are interested in using diverse genotypes in hybridization that can segregate for traits of importance with possibility of selection and genetic gain. Information on molecular and agro-morphological diversity helps the breeders reduce the effort for parental selection and helps the advancement of generations. A phenotypic and molecular diversity study, using 24 traits (agronomic and disease) and 6519 SNPs in a diverse collection of 336 spring barley genotypes, was carried out at Marchouch and Jemma Shiam research stations in Morocco. Based on structure and multivariate analyses, strong differentiation between the two- and six-row types were observed. The linkage disequilibrium (LD) decay of the current collection (for the combined population) was up to 3.58 cM (r 2 = 0.15) while LD decay were estimated 3.91 and 2.36 cM for two- and six-row barley, respectively. PCA of agro-morphological traits revealed grain per spike, net form of net blotch (NFNB), spot form of net blotch (SFNB), and 1000 kernel weight were the most discriminatory traits in the current collection. Association mapping in the two independent populations will be ideal for identification of markers, and QTL related to traits. The generated information on relatedness between individuals will help identify diverse genotypes for breeding programs.  相似文献   
75.
Excess nitrate (NO3-) in lakes and streams has deleterious effects for environmental and human health. Nitrate concentrations have become problematic in agricultural watersheds due to increased use of fertilizers and improper management of livestock wastes. Research has indicated that the planting and/or preservation of riparian buffer zones can be an effective means of reducing pollution from agricultural fields (Osborne and Kovacic, 1993; Jordan et al., 1992; Simmons et al., 1992). Biological denitrification is the most desirable means of nitrate attenuation as the microbial conversion of NO3- removes nitrate from the watershed in the form of N gases. Despite the inherent value of biological denitrification, a comprehensive review discussing the role of this process in removing nitrate from riparian zones is lacking. In this paper we examine the results and conclusions of past research on the topic of denitrification in riparian zones and make recommendations for future research in this area. The need for subsurface denitrification assays in riparian zones is emphasized.  相似文献   
76.
Cyanobacteria are producers of potent and environmentally abundant microcystins, representing an emerging global health issue. In the present study, we investigated the impact of cyanobacterial biomass on biochemical indices of common carp (Cyprinus carpio L., average weight of 246 ± 73 g) under laboratory conditions. The fish were fed a diet containing cyanobacterial biomass with microcystins in high concentration (0.4 mg/kg of fish weight and day) for 28 days. Statistical evaluation of the influence of the cyanobacterial biomass in food on the biochemical indices of the juvenile carp showed only minor differences. The activity of aspartate aminotransferase value and the urea concentration were significantly reduced compared to control group. The biochemical parameters of fish blood plasma significantly rose during the experiment in the control group as well as in the experimental group. This state was probably influenced by the environmental conditions and the fish diet. A significant rising value was established in calcium creatinine, total protein, phosphorus, lactate, urea and natrium. The present study demonstrates that the oral exposure of toxic cyanobacterial biomass has a minor influence on the biochemical indices of common carp and that the effect of other factors, e.g., nutrition is more visible.  相似文献   
77.
78.
A feeding trial was conducted for 60 days to delineate the effect of both gelatinized and non‐gelatinized corn with or without supplementation of exogenous α‐amylase at two level of protein 35% (optimum) and 27% (sub‐optimum) on growth, tissue composition and protein sparing effect of carbohydrate in the diet of Labeo rohita fingerlings. Three hundred and sixty fingerlings (average weight 10.00±0.15 g) were randomly distributed in 12 treatment groups with two replicates for each. Twelve semi‐purified diets containing either 35% or 27% CP were prepared with different levels of α‐amylase (0, 50, 100 and 150 mg kg?1) and starch type [gelatinized (G)/non‐gelatinized, (NG)] viz. T1 (NG, 35% CP, 0 mg kg?1α‐amylase), T2 (G, 35% CP, 0 mg kg?1α‐amylase), T3 (NG, 27% CP, 50 mg kg?1α‐amylase), T4 (NG, 35% CP, 50 mg kg?1α‐amylase), T5 (G, 27% CP, 50 mg kg?1α‐amylase), T6 (G, 35% CP, 50 mg kg?1α‐amylase), T7 (NG, 27% CP, 100 mg kg?1α‐amylase), T8 (NG, 35% CP, 100 mg kg?1α‐amylase), T9 (G, 27% CP, 100 mg kg?1α‐amylase), T10 (G, 35% CP, 100 mg kg?1α‐amylase), T11 (NG, 27% CP, 150 mg kg?1α‐amylase) and T12 (NG, 35% CP, 150 mg kg?1α‐amylase). The fish were acclimatized to the experimental condition for 24 days during which control diet (NG, 35% CP) was fed. Weight gain percentage, specific growth rate, protein efficiency ratio and apparent net protein utilization of NG corn‐fed groups at 42.43% were significantly higher (P<0.05) than the same level of G corn‐fed groups. We conclude that 42.43% NG corn supplemented with 50 mg α‐amylase kg?1 feed at sub‐optimum level of CP (27%) significantly enhanced the growth and protein in L. rohita fingerling. Addition of dietary α‐amylase to G corn had no added advantage on growth of L. rohita fingerling.  相似文献   
79.
In order to investigate the impact of dietary lipid sources on mechanisms involved in lipid deposition, three groups of European seabass fingerlings with average initial body weight of 5.2 ± 1.0 g were fed three diets differing only by lipid source. These diets were: 100% anchovy oil (diet A), 40% anchovy oil-60% mix of vegetable oils (35% linseed, 15% palm, 10% rapeseed) (diet B) and 40% anchovy oil-60% mix of vegetable oils (24% linseed, 12% palm, 24% rapeseed) (diet C). After 64 weeks of rearing, when seabass reached the size of 160 g, the activity of lipogenic enzymes (fatty acid synthetase, glucose-6-phosphate dehydrogenase and malic enzyme) in liver and of lipoprotein lipase (LPL) in perivisceral adipose tissue, liver and white muscle were measured. Transport of lipid by lipoproteins was examined by determining plasma lipid composition and lipoprotein classes. Dietary oil source did not modify growth performance or lipid content of flesh and liver of seabass. Replacement of 60% of fish oil by the two mixtures of vegetable oils had no significant effect on hepatic lipogenesis and activity of LPL in liver and adipose tissue. Activity of LPL in white muscle was decreased in fish fed diet C compared to those fed diets A and B. Diets containing the mixture of vegetable oils led to lowered plasma, VLDL and LDL cholesterol levels compared to diet A.It is concluded that replacing 60% of fish oil by the two mixtures of vegetable oils in the feeds of European seabass fingerlings until they reach the size of 160 g has no marked effect on growth performance, lipogenesis and tissue lipid uptake but has a hypocholesterolemic effect.  相似文献   
80.
We evaluated the influence of dietary nucleic acid (NA) supplied either as an RNA extract (RNA) or as brewer's yeast (BY) on nitrogen (N) utilisation, N excretion and ureogenesis in a freshwater teleost, the rainbow trout (Oncorhynchus mykiss) and a marine teleost, the turbot (Psetta maxima). Five diets containing two levels of NA or BY were formulated for each species, and fed to juvenile rainbow trout (initial body weight (IBW): 21.7 g) and turbot (IBW: 11.8 g) over 8–10 weeks. Besides growth and N utilisation, we monitored total ammonia-N and urea-N excretion rates and measured the activities of selected enzymes (glutamate dehydrogenase, ornithine carbamoyltransferase, arginase and uricase). There was no clear N sparing effect of dietary NA or BY supplementations in either species. Feeding diets containing the RNA extract led to an almost two-fold increase in postprandial plasma urea-N and uric acid concentrations and in urea-N excretion rates. Glutamate dehydrogenase and arginase activities were decreased in fish fed NA supplemented diets. Uricase activities were inversely related to dietary NA levels. Data on N excretion and enzyme activities clearly suggest that ureogenesis is influenced by dietary NA in both species. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
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