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A bioassay of the availability of residual 15N fertilizer eight years after application to a forest soil in interior British Columbia (1994)

Preston, C. M. ; Mead, D. J.

Springer

Plant and soil 160 (1994), S. 281-285

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ISSN: 1573-5036

Keywords: 15N availability ; bioassay ; immobilization ; nitrification ; organic N ; Pinus contorta

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Although a high proportion of fertilizer N may be immobilized in organic forms in the soil, no studies have examined the long-term availability of residual fertilizer 15N in forestry situations. We investigated this by growing lodgepole pine (Pinus contorta) seedlings in surface (0–10 cm) soil sample eight years after application of 15N-urea, 15NH4NO3 and NH4 15NO3 to lodgepole pine in interior British Columbia. After nine months of growth in the greenhouse, seedlings took up an average of 8.5% of the 15N and 4.6% of the native N per pot. Most of the mineral N in the pots without seedlings was in the form of nitrate, while pots with seedlings had very low levels of mineral N. In contrast to the greenhouse study, there was no significantuptake of 15N by trees in the field study after the first growing season, although half of the soil organic 15N was lost between one and eight years after fertilization. This indicates the need to understand the mechanisms which limit the uptake of mineral N by trees in the field, and the possible mismatch of tree demand and mineral N availability.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00010154

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Toward a quantitative theory of the rheology of concentrated solutions of stiff polymers (1991)

Larson, R. G. ; Mead, D. W.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 1271-1285

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ISSN: 0887-6266

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Predictions of the rheological properties of concentrated isotropic solutions of stiff polymers are made that improve on those obtained with the approximate Doi theory. Predictions of the shear-rate and concentration dependence of the viscosity η and the first and second normal stress differences N1 and N2 that avoid the closure approximations of Doi are obtained by using a Galerkin numerical solution for the orientation distribution function. The predictions for η and N1, though they neglect the effects of polydispersity in molecular weight, are shown to be in quantative agreement with recent measurements on solutions of poly-γ-benzyl-L-glutamate (PBLG). The polydispersities of a series of commercial PBLG and PBDG samples are measured by gel permeation chromatography, and found to be broad. An attempt is made to account for the effects of polydispersity on the linear viscoelastic storage and loss moduli for PBLG solutions by using the Marrucci-Grizzuti extension of the Doi theory. The attempt fails. The most probable explanation for the failure is that the rotary diffusive motions of the shorter molecules in the mixture are drastically slowed by the matrix of surrounding longer molecules.

Additional Material: 15 Ill.