Securing Agricultural Productivity by Improving the Soil Water Holding Capacity / SOWAT-IGSSE

Objectives

• Mechanistic understanding of the effects of different organic matter amendments on available water capacity in soil
• Detailed analysis of the chemical composition and structure of organic matter in soil

Method of Approach

• Raman microspectroscopy, Stable isotope Raman microspectroscopy
• Physical fractionation and isotope analysis of soil samples

Description

For an enhanced productivity and reduced economic and environmental consequences of droughts, the soil has to capture and store as much rainwater as possible and further allow the plants to retrieve the adequate amount of water. The development of drought-resistant soils therefore relies strongly on the increase of the available water capacity (AWC), which is closely linked to the soil’s organic matter (SOM) content. The SOM increases the water holding capacity through its influence on the structure and aggregation formation. Aggregates enhance the porosity of the soil through formation of pore sizes that facilitate the storage of water and infiltration of roots.

Since the soil samples consist of different minerals combined with various kinds of organic matter, the analysis of these poses a challenge for the analytical methods. Thus state-of-the-art soil application experiments and Raman microspectroscopy will be combined. Different types of organic matter amendments from established field trials are investigated. Moreover isotope labeled biochar produced from ¹³C enriched crop will be analyzed to examine the fate and transformation of the amendments. The bulk samples undergo physical fractionation and subsequent isotope analysis of to identify the sequested area of the material after decomposition.

The samples are further analyzed by means of Raman microspectroscopy, which is a non-destructive method for characterization of the amendments. Compared to other established methods, Raman spectroscopy (RS) provides characteristic fingerprint spectra of inorganic, organic and microbiological species without sample preparation and low interference of water. The combination of RS with a microscope (RM) enables a high spatial resolution analysis and comparison of optical and spectroscopic images. By means of RM an observation of the soil structural compartments and their temporal changes down to the sub-micrometer range is possible. Due to a red shift of ¹³C compound bands compared to ¹²C compounds, the fate and transformation of the labeled organic matter in the bulk and the fractions obtained by physical fractionation will be investigated (Stable isotope RM, StabI-RM). By combination of RM and StabI-RM with surface-enhanced Raman scattering (SERS) an increased sensitivity of RM analysis can be achieved. Obtained spectroscopic data will be compared with the soil properties. With this strategy we will get information on the effect of different organic matter amendments on the formation of soil structure and aggregation, and thus on the ability of soils to capture plant available water over periods of drought.