C stocks and subsoil management in agroecosystems: application of hyperspectral imaging to study organic matter dynamics in the top one metre of soil

While the demographic pressure for food demand is continuously rising, global environmental changes are threatening the productivity of agroecosystems. Climatic events like floods or droughts, and long-term decrease in soil organic matter stocks due to intensive agriculture are examples pointing to the necessity to find solutions for sustainable performance of agroecosystems.

Significant amounts of water and nutrients are stored in deep soil horizons, and thus subsoil management is being considered as an alternative to sustain high demand in crop productivity.

We used samples from an ongoing field experiment in Germany where the agricultural management was adapted to investigate the potential benefits of deep ploughing with OM incorporation. We recorded hyperspectral images of soil cores (depth = 1 m) using Vis-NIR reflectance spectroscopy and the C distribution within the soil was modeled at a very high spatial resolution (53×53 μm). The SOC mapping revealed an increase in SOC stocks resulting from deep ploughing, and the high resolution images generated allows the observation of OM distribution in the subsoil and the response in SOM stocks to different types of organic matter incorporation (compost vs green manure). The same imaging technique was also combined with solid-state ¹³C NMR measurements to track the molecular composition of the organic amendment during decomposition.

Hyperspectral imaging of soil cores allows the quantification of OM stocks and changes at the pedon scale, and fine scale resolution of heterogeneity in the spatial distribution of soil organic matter is helping to understand and quantify the processes related to changes in soil C stocks in subsoils.