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  • Blackwell Publishing Ltd  (7,052)
  • 1990-1994  (7,052)
  • 1990  (7,052)
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. White rot (Sclerotium cepivorum) causes serious losses in Allium crops throughout the world. The pathogen produces sclerotia which survive for long periods and are the main source of inoculum. Sclerotial germination is stimulated by the host and new sclerotia are produced on the host near the soil surface. Allium crops are cultivated in various systems and environments and no one method of control is effective. There is increasing interest in control strategies based on combinations of treatments which decrease the populations of sclerotia in the soil, thereby improving the effectiveness of present methods of control. Materials and methods being tested for inclusion in programmes of integrated control include germination stimulants, soil fumigants, solar heating, roguing, aerobic composting, microbial control and combined chemical/microbial control with fungicide-resistant micro-organisms.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The relationship between take-all and grain yield was investigated in a first spring wheat crop grown in a field experiment on artificially infested soil. Different incidences and severities of disease were obtained by using different cultivations to incorporate equal amounts of inoculum (killed oat grains colonized by the fungal pathogen) at different depths. The intention of incorporating inoculum at different stages in the same sequence of cultivations to achieve identical soil conditions with inoculum at different depths was not entirely successful because of weather conditions.For most sampling dates and different assessments of disease, there was a strong relationship between yield and disease: regression coefficients were negative and significant (P= 0.01). The linear regression model using logit transformations of disease data from infestations achieved using similar sequences of cultivations accounted for 〉 70% of the variance at all sampling dates, but with untransformed data (percentage plants and percentage roots infected) percentages of variance accounted for were much less at sampling times before anthesis. The plot area affected by premature ripening (whiteheads) also correlated well with yield where similar sequences of cultivations were used, but less well where rotovating to different depths created different soil conditions.The results are discussed in relation to published results from (1) farm surveys, (2) field experiments with natural infection and (3) experiments using different amounts of artificially-produced inoculum. The wider application of artificially-produced inoculum in field experiments on take-all is also considered.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. A rotation trial of four years’ pasture followed by two years’ arable was used to study the effect of cropping on the morphological and hydraulic properties of soil. An adjacent paddock in grass for the past 35 years was included as a permanent pasture reference. Initial infiltration and field saturated hydraulic conductivity (Kfs) were least for cultivated soil and increased with increasing time under pasture. This could be explained by the contrasting porosities of resin-impregnated blocks of undisturbed soil which had been infiltrated with methylene blue dye. Small Kfs values for cultivated soil resulted mainly from a thin surface crust, although pore discontinuity at the depth of the cultivation pan (130 mm) could also have contributed. Greater Kfs values under short-term pasture resulted primarily from water flowing through biogenic pores connected to the surface. The greatest Kfs values were in soil that had been under pasture for 35 years (P35). This was attributed to flow through biogenic pores and fissures associated with the strongly-developed subangular blocky structure. The amount of water that infiltrated the two- and four-year pasture soils (P2 and P4) under ponding was 2.5 and 5 times greater, respectively, than the soil that had been cultivated for two years (C2).As irrigation duration cannot be varied under the border-dyking system used on the Canterbury Plains, the interval between irrigations must be varied if the same total amount of water is to be applied to each of these soils through the season. The interval should be less for the cultivated soil than for those under pasture, and should increase with increasing time under pasture (i.e. P35 〉 P4 〉 P2 〉 C2).
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. N-(n-butyl) thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil and for decreasing ammonia volatilization and nitrite e accumulation in soils treated with urea. It is a poor inhibitor of plant or microbial urease, but decomposes quite rapidly in soil with formation of N-(n-butyl) phosphoric triamide, which is a potent inhibitor of urease activity.The adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to ammonia produced through hydrolysis of urea by soil urease. They can be eliminated by addition of a urease inhibitor to these fertilizers.The leaf-burn commonly observed after foliar fertilization of soybeans with urea results from accumulation of toxic amounts of urea in the soybean leaves rather than formation of toxic amounts of ammonia through urea hydrolysis by leaf urease. Leaf-burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. In most soils of temperate regions nitrate is not held on soil surfaces and moves freely in solution. But when soils carry positive charges, nitrate is held as an exchangeable anion. As a result, leaching of nitrate is delayed relative to the movement of water. The delay can be predicted provided the anion exchange capacity (AEC) can be measured and the concentration of counter-anions is known. For soils with variable charge, the AEC varies with both pH and ionic strength, and the effective AEC should be determined under conditions similar to those in soil solution. A simple leaching method is described which satisfies this requirement. Delays in the leaching of nitrate measured in columns of repacked soil were strongly related to the AEC.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. A brief resumé of the organisms involved in the nitrogen cycle is given. Benefits accruing to micro-organisms are considered in two categories: (1) where the reaction product is incorporated into cells (nitrogen-fixing and nitrate assimilating species), (2) where the reaction is used to provide energy for growth (nitrifying and denitrifying species). Some aspects of nitrogen cycling in soils are briefly considered, including inhibition of nitrification, the importance of C/N ratios and nitrate pollution.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Autotrophic nitrifiers such as Nitrosomonas use ammonia mono-oxygenase for the initial stage of ammonia oxidation. Nitrification inhibitors have this enzyme as their site of action. Their mechanisms include alternative substrates, suicide substrates and cuprous copper chelators.In heterotrophs, organic nitrogen is normally in the fully reduced state, but a few cell metabolites contain N-O bonds. The synthesis and breakdown of such compounds provides a mechanism for heterotrophic nitrification. A non-enzymic mechanism for nitrogen-oxidation involves hydroxyl radicals produced by the Fenton reaction. Heterotrophic nitrification is particularly important in woodland soils, where wood-rotting fungi use free radicals to break down lignin. Tests for a radical mechanism are described.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The workshops covered various aspects of nitrogen in the environment, with special emphasis on the problems posed by nitrogenous compounds as pollutants.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 6 (1990), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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