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  • 1
    Electronic Resource
    Electronic Resource
    Effect of temperature and time of storage of dry soil samples on a chemical index of N availability (1982)
    Springer
    Plant and soil 66 (1982), S. 81-89 
    Details
    ISSN: 1573-5036
    Keywords: Extractable organic matter ; N availability index ; Organic matter ; Organic N ; Soil storage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effect was studied of storage temperature on the index of available soil N wich uses U.V. absorbance of a 0.01M NaHCO3 extract as an indicator. The U.V. absorbance was found to increase at a non-linear rate for four soils stored at temperatures of 50, 75, and 150°C. The change in extract absorbance due to extended soil storage at each of these temperatures was positively correlated to the percent organic matter, percent N, C/N value and concentration of humic substances in soils, but not to the extract absorbance prior to soil storage. These findings were not consistent with room temperature storage data which showed a linear increase in extract absorbance with soil storage time. The change in absorbance for the room temperature case was not related to any of the soil parameters mentioned above. Analysis of a soil stored at 105°C showed an increase in ninhydrin-detectable N, protein N and Kjeldahl N of the NaHCO3 extract, while the apparent molecular weight distribution of extracted organic matter (as determined by gel filtration) showed only a slight change. As a comparison to the NaHCO3 extract, a boiling CaCl2 extract of the same soil was also analyzed; and the absorbance at 260 nm was found to increase in a curvilinear fashion with starage time at 75°C but to less of an extent than was noted with the NaHCO3 extract. Nitrogen availability indexes based on the U.V. absorbance of these extracts, particularly those utilizing the NaHCO3 extract, would be significantly affected by soil storage at elevated temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02203405
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  • 2
    Electronic Resource
    Electronic Resource
    Using NCSWAP to simulate seasonal nitrogen dynamics in soil and corn (1995)
    Springer
    Plant and soil 177 (1995), S. 235-247 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00010130
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  • 3
    Electronic Resource
    Electronic Resource
    Chemical characterization of two extracts used in the determination of available soil nitrogen (1982)
    Springer
    Plant and soil 64 (1982), S. 331-341 
    Details
    ISSN: 1573-5036
    Keywords: Humic substances ; Molecular weight distribution ; N availability index ; Ninhydrindetectable N ; Relative N uptake ; Soil proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two soil extracts used for chemical indexes for N availability, 0.01M NaHCO3 and boiling 0.01M CaCl2, were analyzed in effort to learn more about the nature of the extracted organic matter (O.M.). The two extracts appeared to remove different fractions of the soil O.M. A study of five soils showed that the C/N value of the NaHCO3 extract (following decarbonation) was significantly higher than that of the total soil O.M.; while the C/N value in the boiling CaCl2 extract was not significantly different from that in the soil O.M. There was also significant variation in C/N values among soils for the boiling CaCl2 extract. The extracts of three soils were analyzed for apparent molecular weight distribution using gel filtration and the results compared to those for base-extracted humic substances. Almost all the molecules in the extracts had apparent molecular weights less than 21,000 daltons while 21 to 47% of the humic substances from the same soils (extracted with 0.5M NaOH) had molecular weights greater than 21,000 daltons. In the boiling CaCl2 extract, 78 to 87% of the humic substances had apparent molecular weights less than 1,000 daltons, whereas with the NaHCO3 extract, 42 to 83% of the humic substances were in the 1,000 to 21,000 dalton range. Forty-three to 92% of the N extracted by the NaHCO3 was in protein form, and 8 to 30% was ninhydrin-detectable. In the boiling CaCl2 extract 25 to 30% of the extracted N was ninhydrin-detectable. For the same 10 soils, ninhydrin-detectable N values of the boiling CaCl2 extract appeared closely related to greenhouse and field relative N uptake, while the ninhydrin-detectable N values of the NaHCO3 extract appeared unrelated to both. The protein N and protein in plus ninhydrin-detectable N values of the NaHCO3 extract were closely related to greenhouse relative N uptake only. The results of this study indicated that specific fractions of the soil O.M. were being extracted by the two solutions and that significant differences existed in the chemical nature of the two extracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02372516
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  • 4
    Electronic Resource
    Electronic Resource
    Tillage effect on seasonal nitrogen availability in corn supplied with legume green manures (1994)
    Springer
    Plant and soil 162 (1994), S. 203-210 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01347707
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