Mapping molecular information of organic amendments during their decomposition in soil derived from hyperspectral imaging
Authors: Guigue Julien , Just Christopher , Luo Siwei , Fogt Marta , Schloter Michael , Kögel-Knabner Ingrid , Hobley Eleanor 
Published: March 2021

&lt;p&gt;&lt;span&gt;O&lt;/span&gt;&lt;span&gt;rganic matter added to agricultural soil &lt;/span&gt;&lt;span&gt;determines&lt;/span&gt;&lt;span&gt; the C balance and the nutrient cycling in these ecosystems. Organic fertilisation can result &lt;/span&gt;&lt;span&gt;in&lt;/span&gt;&lt;span&gt; the accumulation of &lt;/span&gt;&lt;span&gt;C in soil but can also stimulate the decomposition of the existing &lt;/span&gt;&lt;span&gt;soil &lt;/span&gt;&lt;span&gt;C pool, as the incorporation of an easily accessible energy-rich substrate often trigger the growth and activity of decomposer. We monitor&lt;/span&gt;&lt;span&gt;ed&lt;/span&gt;&lt;span&gt; the fate of two types of organic material (wheat straw and green manure) during &lt;/span&gt;&lt;span&gt;the first stages of &lt;/span&gt;&lt;span&gt;their decomposition in&lt;/span&gt;&lt;span&gt;to&lt;/span&gt;&lt;span&gt; the soil. For this, we incubated 1-m soil columns &lt;/span&gt;&lt;span&gt;amended&lt;/span&gt; &lt;span&gt;with the two &lt;/span&gt;&lt;span&gt;organic fertilisers either into the topsoil or into the subsoil. We &lt;/span&gt;&lt;span&gt;measured changes&lt;/span&gt;&lt;span&gt; in C and N contents, and &lt;/span&gt;&lt;span&gt;used &lt;sup&gt;13&lt;/sup&gt;C-NMR to resolve the &lt;/span&gt;&lt;span&gt;structural group composition of the added organic material. We also &lt;/span&gt;&lt;span&gt;scanned &lt;/span&gt;&lt;span&gt;the incubated samples &lt;/span&gt;&lt;span&gt;with a hyperspectral camera &lt;/span&gt;&lt;span&gt;and developed predictive models for C to N and for alkyl to O-alkyl ratios at a very fine spatial resolution (53 x 53 &lt;/span&gt;&lt;span&gt;&amp;#181;m&lt;/span&gt;&lt;sup&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sup&gt;&lt;span&gt; per pixel&lt;/span&gt;&lt;span&gt;) for &lt;/span&gt;&lt;span&gt;organic particles in &lt;/span&gt;&lt;span&gt;the whole soil cores.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;he approach based on hyperspectral imaging&lt;/span&gt;&lt;span&gt; was &lt;/span&gt;&lt;span&gt;successful&lt;/span&gt;&lt;span&gt; to follow the decomposition dynamics of POM &lt;/span&gt;&lt;span&gt;during&lt;/span&gt;&lt;span&gt; the incubation, and the associated d&lt;/span&gt;&lt;span&gt;ecreases&lt;/span&gt;&lt;span&gt; in C to N and in&lt;/span&gt;&lt;span&gt;creases in&lt;/span&gt;&lt;span&gt; alkyl to O-alkyl ratios &lt;/span&gt;&lt;span&gt;at a very fine spatial resolution, showing how different part&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; of the organic particles underwent distinct decomposition. &lt;/span&gt;&lt;span&gt;We also observed &lt;/span&gt;&lt;span&gt;contrasting&lt;/span&gt;&lt;span&gt; decomposition dynamics between the wheat straw and the green manure. &lt;/span&gt;&lt;span&gt;This method can bring new information about the first steps of fresh organic matter decomposition in soils and develop our general understanding of the soil organic matter decomposition continuum.&lt;/span&gt;&lt;/p&gt;