THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS II. EFFECT OF AGRONOMIC FACTORS AND SOIL CONDITIONS ON THE DEVELOPMENT OF VESICULAR-ARBUSCULAR MYCORRHIZAL INFECTION IN BARLEY AND ON THE ENDOPHYTE SPORE DENSITY

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Summary

The percentage of roots with vesicular-arbuscular mycorrhizal fungi and numbers of spores were measured over 2 years in a field experiment with different crop rotations of barley, kale and fallow. Spore numbers, and subsequent infections of barley crops, were largest following barley; both kale and fallow breaks reduced spore population and infection similarly. With all crop rotations there was a long delay before appreciable percentage infection of roots developed, followed by a rapid increase, and then a constant value. Such late infections appear unlikely to improve crop nutrition, and final yield was negatively related to per cent infection.

A survey of barley crops in 2 years on commercial fields following at least 3 years barley showed that infection was rather similar in most fields. There was a very slight correlation between infection percentage, clay content and pH, but no other soil factor had any influence. Early-sown crops tended to have low infection.

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