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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Nutrient cycling in agroecosystems 16 (1988), S. 3-13 
    ISSN: 1573-0867
    Keywords: dicalcium orthosilicate ; calcium metasilicate ; mini-granulation ; extractable Si ; Si in saturation extract ; Oxisol ; Andept
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Silicate materials, dicalcium orthosilicate (Ca2SiO4), calcium metasilicate (CaSiO3), and mini-granulated CaSiO3, were incorporated into three highly weathered, low-Si soils. The mixtures were moistened to field moisture-holding capacity and incubated in plastic bags for 60 days at approximately 25°C, after which Si was extracted. Application rates of silicate materials were 0, 460, 920, and 1380 mg Si per kg soil. Two ranges of particles sizes, 0.25 to 0.84 mm and 0.074 to 0.15 mm CaSiO3 and Ca2SiO4 were compared. The soils were a Typic Gibbsiorthox, pH 4.6; a Humoxic Tropohumult, pH 4.2; and a Typic Hydrandept, pH 5.0. Materials were evaluated by four extraction procedures: shaking in water, water displacement from saturated soil, shaking in ammonium acetate solution, and biologically by roots of sugarcane (Saccharum Spp. hybrid). Silicate from the CaSiO3 materials were generally more readily extracted chemically and biologically than silicate from the Ca2SiO4. Solubility and availability of Si usually increased as primary particle size of the silicate materials decreased. The exceptions were associated with the most acid (pH 4.2) Ultisol. Mini-granulation did not reduce the effectiveness of CaSiO3 thus confirming agronomic feasibility of mini-granulation. Plant uptake of Si was most closely related to water-extractable soil Si, followed by Si in saturation extracts and then by NH4 OAc-extractable Si.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 162 (1994), S. 203-210 
    ISSN: 1573-5036
    Keywords: corn ; hairy vetch ; red clover ; nitrogen availability ; tillage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract It has been shown that legume green manures have great potential for replacing a substantial amount of the N fertilizer required for corn (Zea mays L.) production. An experiment was conducted in central Pennsylvania (USA) to study seasonal fluctuation of nitrogen (N) availability in corn with conventional tillage (CT) and no-till (NT) following red clover (Trifolium pratense L.) and hairy vetch (Vicia villosa Roth) green manures double-cropped with winter wheat (Triticum aestivum L.). Samples of corn, weeds, and soil were taken periodically and analyzed for total N content in plant tissue and soil nitrate-N content. The sum of plant N (corn plus weed) and soil nitrate-N in the upper 45 cm profile was used as an indicator of total available N. Under CT, total available N increased rapidly upon legume incorporation and reached 80% of the maximum within 4 weeks. Under NT, total available N increased steadily after the legumes were killed with herbicides and reached a maximum within 7 to 8 weeks. Seasonal corn N accumulations with the legume N source were similar to those where corn followed fallow with 200 kg N ha−1 fertilizer with CT, but were less than those in the same fallow 200 kg N ha−1 treatment with no-till. Dry weather conditions together with weed competition reduced N availability to the no-till corn compared to the CT treatments. The seasonal fluctuations of total available N and corn N uptake suggest good synchronization between N availability from the legume green manures and N accumulation by corn plants in both tillage systems under the conditions of this study.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 177 (1995), S. 235-247 
    ISSN: 1573-5036
    Keywords: corn ; nitrogen availability ; N simulation ; soil ; tillage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The objective of this study was to determine if a re-calibrated version of the computer model NCSWAP (version 36) could accurately predict corn growth and soil N dynamics in conventionally tilled (CT) and no-till (NT) corn supplied with legume green manure or ammonium nitrate as N sources. We also attempted to ascertain the reasons for limitations in the model's ability to simulate corn growth and soil N dynamics found by our colleagues in a previous study and to propose potential improvements. The model was calibrated to accurately simulate total available N (N in plant above-ground biomass plus soil nitrate in the 0 to 45 cm profile) for a control and a fertilizer CT treatment in the 1992 growing season. To do so, input values defining the quantities of active soil organic N had to be reduced to 19% of the values proposed by the model developers and a solute transport factor defining the mobile vs. immobile fractions of soil nitrate adjusted from 0.8 to 0.2. The discrepancies between the proposed values and the lower values employed in this study might be due to the uncertainties in quantitatively describing soil N mineralization processes and the way they are handled in the model, as well as the lack of a component simulating macroporous-influenced water flow and solute transport in the model. With the current version, until one knows how to predict what these values are, the model needs to be re-calibrated for each experimental site and condition and thus is of limited value as a general model. With no further adjustment of input values, model validation success was mixed. The model accurately predicted total available N for treatments in the second year of the experiment that had the same N source and tillage as the treatments used for the calibration year but with the different weather and growing conditions. However, total available N was underpredicted where legume green manure was the N source and overpredicted with no-till cultivation. The model was accurate in simulating seasonal corn growth for nearly all the treatments, judged by nonsignificant mean difference (MD) values and highly significant correlation coefficients (r). Prediction of seasonal soil nitrate concentration was less accurate compared to total available N and corn growth variables. Potential improvements in the model's simulation of a no-till system as well as for predicting corn harvest yield and seasonal soil nitrate concentration where N deficiency occurs were discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 81 (1984), S. 165-176 
    ISSN: 1573-5036
    Keywords: Avocado ; Ca ; Mn ; Oxisol ; P ; pH ; Phytophthora root rot ; Soil water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This experiment employed a factorial design combining 4 soil pH levels, 3 soil moisture levels, with and without the addition ofPhytophthora cinnamomi to the soil to evaluate the conditions that lead to Phytophthora root rot of avocado. An inverse relation between soil pH and leaf production (and root-weight) was observed in nondiseased plants. In soil infested withP. cinnamomi, plant growth and root weights were much depressed by low soil pH, and especially by low soil pH coupled with high soil moisture contents. These interactions were statistically highly significant. Root weights in pots withP. cinnamomi were closely related to the incidence of disease. A disease index was used to visually assess the conditions of roots. Isolation of the pathogen from diseased plant roots confirmed the accuracy of the disease index. A process of elimination suggsts that favorable soil Ca level and not high pHper se was responsible for disease suppression and that the devastating effects of low soil pH was produced by high Mn (and possibly Al) and associated low levels of Ca and P in soil solutions, which led to breakdown of biological control mechanisms.
    Type of Medium: Electronic Resource
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