Root-soil contact of field-grown winter wheat

Roots following existing macropores and voids normally have only partial root-soil contact. Roots penetrating the soil matrix (creating new macropores) initially have complete root-soil contact. Partial root-soil contact may decrease the roots effectivity in taking up water and nutrients. If all roots have complete root-soil contact, however, aeration may be problematic unless roots have a high airfilled porosity. For field-grown winter wheat, root-soil contact was quantified from horizontally oriented thin sections at three depths, 15, 25 and 45 cm, respectively. One day prior to sampling, surface-connected pores were stained by infiltrating a methylene blue solution. Roots were observed microscopically using polarized light, and their diameter, roundness (indicating orientation) and degree of soil contact were measured with a Quantimet 970 image analyzer.No relation was found between root-soil contact and root diameter or roundness. At 45 cm depth root-soil contact was less. For two fields, differing in soil organic matter content and current crop management, a different frequency distribution of root-soil contact was found in the plough layer. The percentage of roots with 100% root-soil contact was 65 and 37, that with 0% root-soil contact 5 and 14, respectively. For roots with partial root-soil contact the average degree of contact was about 60% in both cases. Average root-soil contact for the plough layer of the two fields was 84 and 66%, respectively. Roots without direct contact with the soil were growing mostly in surface-connected (blue stained) macropores. There was no difference in blue staining of the macropores with roots with 1–49% root-soil contact and those of the whole sample. Roots with 50–99% root soil contact occurred mostly in relatively small, non-stained pores.

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DOI:

https://doi.org/10.1016/0016-7061(93)90117-4

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