The effect of cover crops on soil structure is mainly driven by root architecture

Cover crops are known to increase macroporosity and pore connectivity, thus having a beneficial effect on soil hydraulic properties such as saturated hydraulic conductivity, However, cover crop species typically used encompass a variety of contrasting root architectures and their effects on small-scale pore properties are difficult to quantify.

Here we explore the influence of five different cover crops (annual ryegrass, Austrian winter pea, dwarf essex rapeseed, oats, and oilseed radish) on soil structure with X-ray µCT. Undisturbed samples were taken from an experiment with these cover crops on Kellogg Biological Station (Michigan, USA) in October 2019. Two soil columns with a diameter of 5 cm were taken in 5 - 10 cm depth from each of three replicated plots per plant species and scanned with X-ray µCT at a resolution of 18 µm.

These images will be used to characterize pore structure in terms of pore size distribution, pore connectivity. In addition, a new imaging protocol will be used, which combines existing ones with a random forest classifier to segment image features such as pores, biopores and roots simultaneously.

First, the results reveal that different cover crops indeed result in different pore characteristics.  The fibrous root system of oats leads to the highest volume of narrow macropores and increased their connectivity, while the tap root system of dwarf essex rapeseed mainly effected wide macropores.  The highly diverse root system of Australian winter pea increased a wide range of pore sizes and thus resulted in the highest visible porosity.

The current study is funded by a grant from USDA Organic Transition program