Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure

The effect of different tillage-fertilization practices on the mycoflora of wheat grains

A two-factor field experiment was carried out at the Lithuanian Institute of Agriculture during the period 2005-2008. The influence of different tillage and fertilization practices on wheat grain fungal contamination was evaluated. Grain surface contamination and internal grain infection with fungi were quantified using agar tests. Purified colonies were identified using different manuals. A total of 16 fungal genera were identified in spring and winter wheat grains. Alternaria infected 46.3% - 99.9%, Cladosporium 26.9% - 77.8%, Fusarium 0.9% - 37.1%, Penicillium 1.3% - 2.5% of grains tested. Winter wheat grain surface contamination by fungi ranged from 7.2 × 103 to 24.8 × 103 of colony forming units per g of grain (cfu g-1), spring wheat from 14.8 × 103 to 80.3 × 103 cfu g-1. No-tillage increased winter wheat grain infection by Alternaria, Aspergillus and Cladosporium species and total count of cfu g-1 on spring wheat grain surface. High fertilizer rates resulted in an increase in spring wheat grain infection by Fusarium and Penicillium species and total count of cfu g-1 on both spring and winter wheat grain surface.