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Seetha Ananth

Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

Diane H. Rickerl


Vesicular-arbuscular mycorrhizal (VAM) fungi have been shown to promote crop growth by several authors, mainly by improving phosphorus uptake. Agricultural management practices such as crop rotation, tillage, fertilization etc. can considerably change the environment which the VAM fungi inhabit. Several studies have shown that mycorrhizal infection in roots is reduced by soil disturbance. A two year study was conducted in 1989 and 1990 at three sites located in eastern South Dakota to investigate the effects of different management practices on mycorrhizal infection in roots and spore distribution in the soil. The two studies at the northeast location were designed to compare three rotation systems: conventional, alternate and ridge-till (study one) or minimum-till (study two). study one emphasized row-crops, corn [Zea mays L.] and soybean [Glycine max (L.) Merr.], while study two emphasized small grains, spring wheat (Triticum aestivum L.], barley [Hordeum vulgare L.] and oat (Avena sativa L.]). The study at the southeast location was designed to compare mycorrhizal infection in rotated or non-rotated corn at two phosphorus rates (0 and 582 kg P2O5 ha-1). Crop sequences of corn/soybean, corn/oat, corn/fallow and corn/corn were grown under two tillage systems, moldboard plow and ridgeplant. Ridging adversely affected mycorrhizal infection in soybean roots more than in corn in study one. However, at the southeast location similar reductions were noticed in corn also. Farming system did not significantly affect mycorrhizal infection in study two. The typical three-phase infection pattern was seen only in soybean roots. The other crops did not exhibit the initial lag phase. Considerable infection occurred as early as three weeks after planting in all the studies. Spore numbers were not significantly different with cropping system in all the three studies, but were significantly different with depth. Spore populations were significantly higher in the 45-60 cm depth at all locations. Soil phosphorus concentration was correlated with spore accumulation at these depths only in the southeast location. At the southeast location spores of the genus Gigaspora dominated, while members of the genus Glomus were abundant in the northeast location.

Library of Congress Subject Headings

Vesicular-arbuscular mycorrhizas
Roots (Botany) -- Diseases and pests
Cropping systems




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