The effect of arbuscular mycorrhiza on biomass production and phosphorus uptake from sparingly soluble sources by leek (Allium porrum L.) in Finnish field soils

The effect of inoculation by arbuscular mycorrhizal fungi (AMF) and indigenous AMF populations on biomass production and phosphorus (P) uptake by leek and on its utilization of P in Kola apatite and bone meal was studied in field soils. Arbuscular mycorrhiza (AM) did not enhance P uptake from KoIa apatite, which had no clear effect on P uptake by leek within one growing season, either in the field or in pots. AM increased P uptake from bone meal by 62% in a pot experiment. Inoculation did not increase the effect in unsterile soil as compared with the indigenous AMF populations. The results demonstrate a key role for AM in utilization of organic P. On conventionally managed soil monocropped with cereal, inoculation increased growth and P uptake by leek by 62 and 73%, respectively, in contrast to organically cultivated soil where it had a slight negative effect. The difference in the inoculation effect was concluded to be due to the more abundant and effective indigenous AMF populations in the organically cultivated soil. This was suggested by the fourfold higher spore density at the start of the trials and larger root colonization in the organic cropping system as well as by the fact that the inoculation effect was not dependent on fertilization. Superphosphate application in the conventional system resulted in soil P availability comparable to that in the organic system. Management history was the only important factor influencing AM effectiveness which was different on the two experimental sites. The results suggested that regular inoculation is not an appropriate AM utilization strategy in a sustainable farming system. The hypothesis for further study is that utilization of the indigenous AMF by system management would have more potential in sustainable agricultural practices.