There are quite a lot of things to consider from the biology as much as the analytical aspect with these experiments. There are a lot of recent papers on the topic (Hill & Jones, 2018 New Phyt is a good recent one), which also incorporate more up to date info on uptake of organic N by plants which adds further complexity. Sadly there's definitely no rule of thumb on NO3:NH4 ratio.
Whatever you decide to do, the most critical thing is having mirrored controls i.e. 15NO3-14NH4 and 14NO3-15NH4 - this way you present the same question to the plant in each treatment. A control without any addition is also useful, but the bigger issue here is presenting the 'choice' of the two N forms to provide a real understanding of preference. Otherwise, the question you're actually testing is how the plant responds to an excess of one form or another, and not whether it has a preference for the uptake of one form or the other in equal terms.
A further complication is of course matching application rates of the label to something ecologically relevant.
Dr Mark Farrell
Principal Research Scientist
Team Leader - Soil Biogeochemistry
E [log in to unmask] T +61 8 8303 8664
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On 27/9/18, 22:59, "Stable Isotope Geochemistry on behalf of Wolfram Meier-Augenstein (pals)" <[log in to unmask] on behalf of [log in to unmask]> wrote:
If memory serves, rates for N-uptake by plants as ammonia N and as nitrate N are 66 % and 34 % respectively.
Assuming plant samples (as freeze-dried, milled plant matter) are being analysed for total 15N by EA-IRMS, fertilizer with an enrichment level of 10 % APE 15N should be ample.
Assuming further your colleagues are interested in comparing N-uptake from ammonium N to N-uptake from nitrate-N, they would need to run a side-by-side study of at least three plots all but identical for fertilizer application, e.g. plot 1 has X kg of ammonium nitrate (10 % APE ammonium 15N) applied; plot 2 has X kg of ammonium nitrate (10 % APE nitrate 15N) applied; plot 3 has no fertilizer applied and serves as control (no N fertilizer; up-take of soil background 15N).
BTW, a fertilizer study on tomato plants has shown better N-uptake if fertilizer was applied in liquid form (solution) as compared to applying fertilizer is solid form (e.g. pellets).
Here are a few papers / book chapters on this subject.
D. Barraclough published a paper in Plant and Soil (1991; 131: 89-96) on 15N tracer experiments and how to interpret them.
The tomato study was published by Nakano und Uehara in Japan Agricultural Research Quarterly (2007; 41: 219-226).
Nadelhoffer, K.J. & Fry, B. contributed a chapter on "Nitrogen isotope studies in forest ecosystems" to the book Stable Isotopes in Ecology and Environmental Studies (1994; Eds K. Lajtha & R.H. Michener), pp. 22-44.
H. Dinkelmeyer et al. published a study if N-take from 15N labelled ammonium sulphate in Agroforestry Systems (2003; 57: 231-224).
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Jose Manuel Moreno Rojas
Sent: 27 September 2018 13:11
To: [log in to unmask]
Subject: [ISOGEOCHEM] Attempt to mark plants with fertilizers
Some colleagues are trying to convince to work on plants by marking them with fertilizers. They explained me that find several options in the webpage they checked:
AMMONIUM NITRATE (NITRATE-15N, 10%)
AMMONIUM NITRATE (NITRATE -15N, 98%)
AMMONIUM NITRATE (AMMONIUM-15N, 10%)
AMMONIUM NITRATE (AMMONIUM-15N, 98%)
AMMONIUM NITRATE (15N2, 10%)
AMMONIUM NITRATE (15N2, 98%)
AMMONIUM SULFATE(15N2, 99%)
AMMONIUM SULFATE(15N2, 10%)
Since they do not use to work with isotopes and I do not use to work with this type of products I am worried about how to manage that experimental work (and the later analysis). They provide me with this
Anybody out there with experience in this kind of works could help me?.
I would need which procedure is more convenient to mark the plants, formulations, etc. I do not know if there are other webs providing this kind of materials since they seems to be expensive.
Any advice would be wellcome.
José Manuel Moreno Rojas, PhD
Head of the Department of Food Science and Health IFAPA Centre "Alameda del Obispo"
Avda. Menéndez Pidal, s/n. 14071 Córdoba, Spain.
tel.: +34 671532758 (632758); fax: +34957016043
email: [log in to unmask]
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