Dissolved Organic Matter (DOM) distribution in soil

Dissolved Organic Matter (DOM) plays an important role in the growth of plants. DOM provides numerous benefits to plant growth due to its molecular structure. It helps to break up clay and compacted soils, assists in transferring nutrients from the soil to the plant and enhances water retention. To understand the dynamics of plant growth it is important to know how DOM is distributed throughout the soil.

Two of the major components of DOM are humic materials, degradation of plant material and proteins. Both fractions can be measured by fluorescence. Most fluorescence studies that have been carried out in the past measured only at single excitation and emission wavelengths (λex=330 nm; λem=450 nm). These wavelengths would only represent the humic materials and provide no information about the composition and properties of the DOM.

The Skalar Fluo-Imager, based on the unique Spectral Fluorescence Signatures (SFS) technique, uses 3-dimensional fluorescence excitation-emission spectroscopy. With this technique, a three-dimensional graph is measured of fluorescence intensity as a function of the excitation and emission wavelength. Applying the SFS technique provides more detailed information on the DOM, including the proteins. Occurrence of specific fluorescence characteristics will give information on the composition and sources of the DOM.

An example of a Spectral Fluorescence Signature (SFS) of DOM in a soil extract is given in the figure below. This graph shows clearly the different components of DOM, humic materials and proteins.

To measure the distribution of DOM, humic material and proteins in soil, samples were taken and sliced into parts of one centimeter. These slices were extracted with water and the extract was measured with the Skalar Fluo-Imager. The graphs below show some of the measurements of the different slices.

When the fluorescence of the proteins and the humic material are plotted against the depth of the soil sample, the distribution of the different components of the DOM throughout the soil is obtained.

It shows clearly that almost all of the proteins are present in the first 10 cm of the soil, where the amount of humic material increases with the depth, even as deep as 25 cm.

The combination of less intensive sample pre-treatment, information about all the different aspects of the DOM and the fast analysis time of less than two minutes, makes the Skalar Fluo-Imager a very powerful tool in the investigation of the DOM distribution in different soils.

For more information on the Skalar Fluo-Imager or other Skalar products, please contact Skalar Analytical BV