DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS .2. EFFECT OF AGRONOMIC FACTORS AND SOIL-CONDITIONS ON THE DEVELOPMENT OF VESICULAR-ARBUSCULAR MYCORRHIZAL INFECTION IN BARLEY AND ON THE ENDOPHYTE SPORE DENSITY

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. Copyright © 1979, Wiley Blackwell. All rights reserved