COLONIZATION OF WHEAT BY VA-MYCORRHIZAL FUNGI WAS FOUND TO BE HIGHER ON A FARM MANAGED IN AN ORGANIC MANNER THAN ON A CONVENTIONAL NEIGHBOR

Levels of colonisation by vesicular-arbuscular (VA)-mycorrhizal fungi were compared between adjacent farms, one operated in a conventional m anner and the other run according to organic farming principles. Wheat grown on the organic farm was found to have VA-mycorrhizal colonisati on levels consistently 2 to 3 times higher than wheat on the conventio nal farm. Glasshouse and field trials indicated that the lower colonis ation levels on the conventional farm were due to continual use of fer tiliser containing soluble phosphorus (P). The fertiliser appeared to have an immediate negative effect on the rate of colonisation, and als o appeared to have a long term negative effect through maintaining hig her levels of soluble P in the soil, and by decreasing inoculum levels . Use of the relatively insoluble reactive rock phosphate fertiliser o n the organic farm did not decrease levels of VA-mycorrhizas. Colonisa tion levels did not vary between wheat varieties, and herbicides and s eed dressings were also not found to be having any significant effect on levels of colonisation.