Effect of incorporation of Brassica napus L. residues in soils on mycorrhizal fungus colonisation of roots and phosphorus uptake by maize (Zea mays L.)

Plants in the Brassicaceae family are known to contain thioglucoside compounds that produce isothiocyanates when tissues are disrupted. These chemicals have a negative effect on soil-borne fungal pathogens, and possibly on vesicular–arbuscular mycorrhizal (AM) fungi. We investigated the effect of incorporation of Brassica napus L. residues in a soil on mycorrhizal colonisation of roots, P uptake and growth of following maize (Zea mays L.) crop. A pot experiment was carried out in a glasshouse with pre-inoculation with Glomus intraradices (+I and −I), incorporation of B. napus L. residues (+R and −R) and mineral P fertilization (+P and −P) as studied factors. The soil used was a neutral loamy soil with low P availability. The pots were planted with maize (Z. mays L.). Phosphorus uptake, plant biomass, total leaf area per plant and area of individual leaves (rank 4–7) were significantly larger in +P treatments than without P addition, thus confirming that the soil used for the experiment was P deficient. Incorporation of B. napus L. residues had also a positive effect on P uptake, plant biomass, total leaf area per plant and area of individual leaves (rank 5–7). These effects were more pronounced in −P treatments than in +P treatments. There was no effect of pre-inoculation with G. intraradices on P uptake and P dependant variables. The percentage of the root length that was colonised by mycorrhizae was lower in +P treatments but it was not significantly affected by other studied factors. Altogether the results showed that B. napus L. residues have mainly acted as a source of P. There was no evidence of a negative effect of the incorporation of B. napus L. residues on the colonisation of maize roots by mycorrhizae.