Impact of cropping system on mycorrhiza

Summary

The impact of cropping system on field communities of mycorrhizal fungi was studied utilising a long-term experiment on a loamy soil. Two contrasting crop rotations each with two fertilisation regimes were compared. The conventional crop rotation (barley-barley-rye-oat-potato-oat) was fertilised at either full or half the normal recommended rate. In the low-input crop rotation, one year with barley was replaced by clover, and oat was cultivated in mixture with pea. For this rotation biotite and raw phosphate was used to compensate for the K and P of the harvested yield; animal manure was used at the beginning only. Clover and straw were returned to the soil either directly or after composting. Mycorrhizal infectivity and effectiveness were studied in bioassays in the growth chamber, and the spore densities of mycorrhizal fungi as well as their species composition in the field were determined. Only the low-input system with application of compost conclusively favoured mycorrhiza, in comparison to some or all of the other systems depending on time and function. The low-input system with no compost was more favourable than the conventional systems in terms of growth effect in 1996, but in 1997, clover incorporation markedly inhibited mycorrhiza in comparison to the other systems. Inhibition of mycorrhizal functions may indicate general mismanagement and imbalance in the soil ecosystem. This stresses the need for further studies on the importance of composting easily decomposable organic matter prior to soil incorporation for management of soil quality.