Functional root trait‐based classification of cover crops to improve soil physical properties

Abstract

Cover crop use is a well‐established soil conservation technique and has been proven effective for erosion control and soil remediation in many arable systems. Whereas the obvious protection mechanism of cover crops occurs through the canopy, plant roots perform multiple functions. It is important to consider the soil functions delivered by different root systems in order to increase the uptake of cover crops for sustainable soil and water management. A classification of cover crop root systems up to 0.6 m deep based on functional traits will allow us to better study their potential role in soil bio‐engineering, soil structural improvements for hydrological services and soil resource protection. This was a glasshouse experiment, using large 1‐m3 containers filled with loam soil, loose topsoil and compacted subsoil, in which seven cover crop species (oat, rye, buckwheat, vetch, radish, mustard, phacelia) were grown for 90 days. Root cores were taken at the end of the experiment, washed and imaged to determine root traits (total root length density, average root diameter, root specific length and root surface area) for both the topsoil and subsoil layers. Root identity was determined from a distinctive combination of single root traits and related to three soil functional variables, representing soil structural improvement, runoff mitigation and erosion control. The results showed that total root length and root surface area correlate well with aggregate stability and soil macroporosity. Buckwheat, mustard and rye had significantly greater aggregate stability, as well as 10, 8 and 7% greater microporosity, respectively, at the interface with the compacted layer when compared to the control bare soil. Furthermore, average root diameter negatively correlated with soil macroporosity, indicating that cover crops with a fine root system are more beneficial for creating pore‐space than those with thicker taproots. Selecting cover crop species with the right root traits is therefore crucial to improve soil health. Highlights Roots of cover crops are a largely unexplored frontier for bio‐engineering of agricultural soils. Combinations of root traits were identified that most improve soil characteristics. Cover crops with finer root systems were better at enhancing porosity. Root length and surface area were most important for enhancing soil structure.

Cover crop monocultures and mixtures affect soil health indicators and crop yield in the southeast United States

“…Additionally, a greenhouse study by Hudek et al. (2021) found some species of brassica cover crops increased aggregate stability and that all brassicas tested decreased penetration resistance compared with no cover crop in the top 25 cm of soil.…”

“…However, a study in Idaho found that radish (Raphanus sativus L.) cover crops increased aggregate stability after 2 yr (Lehrsch & Gallian, 2010). Additionally, a greenhouse study by Hudek et al (2021) found some species of brassica cover crops increased aggregate stability and that all brassicas tested decreased penetration resistance compared with no cover crop in the top 25 cm of soil. Many studies have examined the effect of cover crops on soil properties in the Southeast.…”

Response of spring barley root and soil physical properties to changes under cover crop and different tillage

“…The root volume positively correlated with the soil macroporosity (r = 0.40, P < 0.05) and the total porosity (r = 0.41, P < 0.05), and the correlation with the bulk density (r = −0.41, P < 0.05) was negative. Hudek et al (2021) also reported that the total root length and root surface area had a significant effect on soil microporosity. Bodner et al (2014) found that greater root density significantly increased the micropore volume by cover crops, but in the meantime reduced the volume of larger pores.…”

“…Furthermore, Haruna et al (2018b) found that CC management increased water infiltration parameters. According to Hudek et al (2021), CC significantly increased aggregate stability and microporosity. However, the impact of CC on soil physical properties is inconsistent (Zaibon et al, 2016;Haruna et al, 2018a;Çerçioğlu et al, 2019), and some studies have shown no effect of cover crops on soil properties.…”

Legume cover crop type and termination method effects on labile soil carbon and nitrogen and aggregation

“…Other research has shown that cover crops can ameliorate the effect of tillage, but only after 10 yr of the same management and in a nonlegume cover crop (Abdollahi & Munkholm, 2014). Fine roots of cover crops and microbial secondary metabolites are known to facilitate the formation and stability of soil aggregates (Hudek et al., 2021; Jastrow et al., 1998). Our data demonstrates that even in the 1st year, CT decreases aggregate MWD relative to FM when cover crops are not planted.…”