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  • 1
    Electronic Resource
    Electronic Resource
    Changes in 15N abundance and amounts of biologically active soil nitrogen (1999)
    Springer
    Biology and fertility of soils 30 (1999), S. 69-74 
    Details
    ISSN: 1432-0789
    Keywords: Key words 15N-microbial biomass C ; Microbial biomass N ; Mineral-N ; Texture ; Active soil N
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Estimation of the capacity of soils to supply N for crop growth requires estimates of the complex interactions among organic and inorganic N components as a function of soil properties. Identification and measurement of active soil N forms could help to quantify estimates of N supply to crops. Isotopic dilution during incubation of soils with added 15NH4 + compounds could identify active N components. Dilution of 15N in KCl extracts of mineral and total N, non-exchangeable NH44 +, and N in K2SO4 extracts of fumigated and non-fumigated soil was measured during 7-week incubation. Samples from four soils varying in clay content from 60 to 710 g kg–1 were used. A constant level of 15N enrichment within KCl and K2SO4 extracted components was found at the end of the incubation period. Total N, microbial biomass C and non-exchangeable NH4 + contents of the soils were positively related to the clay contents. The mineralized N was positively related to the silt plus clay contents. The active soil N (ASN) contained 28–36% mineral N, 29–44% microbial biomass N, 0.3–5% non-exchangeable NH4 + with approximately one third of the ASN unidentified. Assuming that absolute amounts of active N are related to N availability, increasing clay content was related to increased N reserve for crop production but a slower turnover.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050589
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  • 2
    Electronic Resource
    Electronic Resource
    Interaction of urea with triple superphosphate in a simulated fertilizer band (1993)
    Springer
    Nutrient cycling in agroecosystems 36 (1993), S. 35-44 
    Details
    ISSN: 1573-0867
    Keywords: acid soils ; P diffusion ; pH ; triple superphosphate ; urea ; urea hydrolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Fertilizer nutrient diffusion from fertilizer bands and transformations in soil can affect fertilizer nutrient availability to crops and knowledge of the transformations is necessary for proper management. The interaction of urea and triple superphosphate (TSP) on urea hydrolysis and P transformations during diffusion processes from a fertilizer band was evaluated in a laboratory incubation experiment with two eastern Canadian soils (Ste Rosalie clay, Modifiers Typic Humaquept, pH 5.0; Ormstown silty clay loam, Modifiers Typic Humaquept, pH 6.0). Two fertilizer sources (urea and TSP) and three N and P rates (0, 100 and 200 kg ha−1) were combined in a factorial arrangement. Fertilizer combinations were placed on segmented soil columns, incubated and segments were analyzed for N and P content. Acidification from dissolution of TSP retarded urea hydrolysis, and curtailed the rise in soil pH surrounding the fertilizer band. Urea hydrolysis caused dissolution of organic matter in soils, which might inhibit precipitation of insoluble phosphates. Banding urea with TSP increased 1M KCl extractable soil P, soil solution P, sorbed P concentration and total P diffused away from the band. Urea decreased 0.01M CaCl2 extractable P, indicating probable precipitation of calcium phosphates with CaCl2 extraction. Banding urea with TSP could benefit P diffusion to plant roots in low Ca soils and increase fertilizer P availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00749946
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  • 3
    Electronic Resource
    Electronic Resource
    Availability of banded triple superphosphate with urea and phosphorus use efficiency by corn (1999)
    Springer
    Nutrient cycling in agroecosystems 53 (1999), S. 237-248 
    Details
    ISSN: 1573-0867
    Keywords: corn ; phosphorus efficiency ; triple superphosphate ; urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus fixation results in low P use efficiency in acid soils. Increase in soil pH through urea hydrolysis may improve P availability and use efficiency. Growth chamber and field experiments were conducted to evaluate effects of urea on triple superphosphate (TSP) transformation and P use efficiency. A Ste. Rosalie clay (Typic Humaquept), an Ormstown silty clay loam (Typic Humaquept) and a Chicot sandy clay loam (Typic Hapludalf) were used in the growth chamber experiment with three rates of N (0, 200 and 400 mg N kg-1), two N sources, either urea or NH4 NO3, based on 87 mg P kg-1 soil. In the field, three rates of urea (0, 60 and 120 kg N ha-1) and two rates of TSP (26 and 52 kg P ha-1) were compared on a Ste. Rosalie clay and an Ormstown silty clay loam. Compacted or blended mixtures of urea-TSP with different ratios of N:P were used in the field experiment. In the growth chamber experiment, soil pH and dissolved organic carbon (DOC) concentration was increased by added urea, and Mehlich (3) and water extractable P thus increased with increased urea. Soil pH, DOC and available P levels were not significantly affected by added NH4 NO3. Phosphorus uptake increased with added N, either urea or NH4 NO3, but P concentration increased only with addition of urea. In the field, soil Mehlich (3)-P at day 20, P uptake and use efficiency, corn yields increased when urea was applied with TSP. Compacted mixtures of urea-TSP increased P uptake and use efficiency, corn yields in comparison with blended mixtures. The beneficial effects of banded urea with TSP on P availability and P use efficiency were primarily attributed to urea hydrolysis, subsequent pH increase and organic matter dissolution as well as synergistic effect of N and P. These results indicate that compaction of urea plus TSP may offer a significant advantage over blended mixtures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009776706425
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