Abstract
Nuclear magnetic resonance (NMR) techniques are largely employed in several fields. As an example, NMR spectroscopy is used to provide structural and conformational information on pure systems, while affording quantitative evaluation on the number of nuclei in a given chemical environment. When dealing with relaxation, NMR allows understanding of molecular dynamics, i.e., the time evolution of molecular motions. The analysis of relaxation times conducted on complex liquid–liquid and solid–liquid mixtures is directly related to the nature of the interactions among the components of the mixture. In the present review paper, the peculiarities of low resolution fast field-cycling (FFC) NMR relaxometry in soil science are reported. In particular, the general aspects of the typical FFC NMR relaxometry experiment are firstly provided. Afterwards, a discussion on the main mathematical models to be used to “read” and interpret experimental data on soils is given. Following this, an overview on the main results in soil science is supplied. Finally, new FFC NMR-based hypotheses on nutrient dynamics in soils are described
Highlights
The locution “nuclear magnetic resonance”, indicated with the acronym Nuclear magnetic resonance (NMR), refers to a multifaceted technique which can be applied to liquid [1], semisolid [2], solid [3], and gas [4] phases.It can be used to unveil the structure of pure chemical compounds [5], and the chemical complexity of mixtures [6], as well as that of living organisms [7,8].Notwithstanding the vast areas of expertise covered by the NMR techniques and their different aspects related to sample preparation, instrumentation, and targeted results, all of them share the same principles [9]
We are well aware that fast field-cycling NMR relaxometry is a technique that remains accessible to a small number of specialists
fast field-cycling (FFC) NMR results are not as readable as those from spectroscopy, thereby making the former less popular in soil science than the latter, which is very often misused in the field [3,11,12,137]
Summary
The locution “nuclear magnetic resonance”, indicated with the acronym NMR, refers to a multifaceted technique which can be applied to liquid [1], semisolid [2], solid [3], and gas [4] phases. Once the NMR experiments are set to measure relaxation times (either T1 or T2 ), the time dependent resonance signals can be handled with the inverse Laplace transform to produce relaxograms (either 1D or 2D), where distribution of relaxation times are represented [13,14,15,16,17] This technique, named time-domain (TD) NMR, is applied to obtain information on molecular dynamics either for simple systems or complex mixtures [18]. The technique, named fast field-cycling (FFC) NMR relaxometry, aims at the evaluation of the molecular motions included in the time scale ranging between 10−8 to 10−3 s [20]. FFC NMR relaxometry is intended as the technique by which the T1 values are monitored when the strength of the applied magnetic field is varied within a given proton Larmor frequency interval. In soils can influence movement of nutrients towards plant roots
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