Root Distribution of Brassica napus and Vicia faba within the Sheath of Root or Earthworm Biopore

Lisa Petzoldt,Timo Kautz

doi:10.3390/agriculture11010061

Abstract

Root growth through biopores is facilitated by low mechanical impedance and nutrient enrichment due to the deposition of organic material at the biopore sheath. Plant roots and earthworms impact biopore sheath properties differently. However, the literature lacks a quantitative study of the root distribution within the sheath of pores, which were originated by taproots or earthworms. According to previous literature on pore connectivity, it can be hypothesized that precrops encourage root growth into the biopore sheath in comparison to an earthworm characterized sheath. A pot experiment was performed to compare the root distribution of spring oilseed rape (Brassica napus L.) and faba bean (Vicia faba L.) within the biopore sheath of two different biopore types. The biopore sheath was characterized by taprooted chicory (Cichorium intybus L.) or anecic earthworm (Lumbricus terrestris L.). Roots were sampled at the biopore lumen and at lateral distances of 0–2, 2–4, 4–8 (sheath) and 20–36 mm (bulk soil) from the biopore wall surface. In both pore types >50% of the root length (cm) and >70% fine roots of oilseed rape were found in a comparatively small soil area (Lumen + 2 mm). On the contrary, faba bean grew primarily through the bulk soil with >75% root length and rarely into the biopore sheath in both pore types. In both species there was a lateral decrease of the total nitrogen (Nt)-content from biopore wall (Mean ± SE: 0.061% ± 0.002%) to bulk soil (0.053% ± 0.002%), but no significant difference between the pore types. The results of the current study illustrate that the root growth of spring oilseed rape and faba bean was not encouraged by the precrop in comparison to the earthworm characterized sheath.

Highlights

Biopores are predominantly formed by earthworms and plant roots
This study focuses on root and worm type biopore sheaths and their effects on the root distribution of two allorhizous crops by investigating the following hypotheses: (i) The RLD and the share of fine roots is higher in the biopore sheath (0–8 mm) of root type than of worm type biopore, (ii) there is a higher RLD of oilseed rape in the biopore sheath than of faba bean, and (iii) the decrease of the Nt- and Ct-content is sharper in the worm type than in the root type biopore sheath from biopore surface until 8 mm distance from macropore
Tvheerraellw, tahsenRoLdDiffoefrfeanbcae beatwnewenasthleesRs LthDanintthheeRshLeDatohfaonildsebeudlkrape and the soil of both tvyapreisa.nOceveorfatlhl,ethReLRDLwDaosfhfiagbhaebrefaonr fwabaas lbeesasnth. an the RLD of oilseed rape and the variance of the RLD was higher for faba bean

Summary

Introduction

Biopores are predominantly formed by earthworms and plant roots. Large-sized biopores (diameter >5 mm) are cylindrical shaped continuous macropores found in untilled soil layers. Roots and earthworms may interact when forming those pathways, or they may occupy them alternately, but both influence the properties [1,2]. In studies on large-sized biopores the effect on root growth within the sheath has not been considered. Based on the characteristics of the sheath, root-soil contact can be encouraged or diminished. This can be important for nutrient acquisition

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Discussion

Conclusion