Abstract
Cover crops (plants grown in an agricultural rotation between cash crops) can significantly improve soil quality via sequestering carbon, retaining nutrients, decreasing soil erosion, and maintaining belowground biodiversity. However, little is known about the effects of such plants upon soil structure. The aim of the study was to assess the impact of four species typically used as cover crops and which have contrasting root architecture (viz. clover, black oat, phacelia, tillage radish) on soil structural genesis and the associated modification of microbial community structure in a clay soil. The four plant species were grown in a replicated pot experiment with sieved soil (<2 mm), with unplanted soil as control for 8 weeks. X-ray Computed Tomography was used to quantify the formation of pore networks in 3D and phospholipid fatty acid analysis was performed to characterise the microbial community phenotype. Black oats developed a greater soil-pore connectivity than the other species throughout the growth period, whereas phacelia decreased both the porosity and pore-connectivity. The microbial community phenotype under phacelia was notably different from the other species, with a greater proportion of fungal markers. Thus, different plant species have differential effects upon soil structural genesis and microbial community phenotype, which provides evidence that certain species may be more suitable as cover crops in terms of soil structural conditioning depending upon specific contexts.
Highlights
Soil structure is an important factor affecting crop production, primarily due to the influence that the soil pore network exerts on root growth, soil fauna, nutrient, water and gas exchanges[1]
We hypothesised that different root morphologies would influence soil structural genesis dependent upon the root phenotype: for example, tap root species may initiate concentric compaction surrounding the primary root, decreasing porosity and diversity of pore sizes, compared to fibrous root species which may create a greater diversity of pore sizes, increasing porosity and pore-connectivity
Re-arrangement of aggregates might be different depending on the root morphologies as black oat has generally thicker and more structured root architecture compared to phacelia which has thinner roots with less organized structure[14,23]
Summary
Soil structure is an important factor affecting crop production, primarily due to the influence that the soil pore network exerts on root growth, soil fauna, nutrient, water and gas exchanges[1]. X-ray Computed Tomography (CT) can non-destructively image the soil pore networks and plant root morphology[14,19,20] By using this technique, it was revealed that cover crops induced contrasting behaviour to changes in soil bulk density[14]. Our aim here was to assess the impact of four species of plants commonly grown as cover crops in the UK (white clover, black oat, phacelia, tillage radish) on soil structural genesis and modification of microbial community structure. These plants were selected for their contrasting root morphologies in terms of tap root formation, vigorous deep-rooting and fibrous multi-branching root systems. X-ray CT was used to quantify the formation of pore networks in 3D and phospholipid fatty acid (PLFA) analysis was performed to study the microbial community phenotype
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