ICOM1 Abstract

BEARDEN, BIRGITTE NEERGAARD. The Royal Veterinary and Agricultural University, Department of Chemistry, 40,Thorvaldsensvej, DK-1871 Frederiksberg C, Denmark. - Influence of arbuscular mycorrhiza on aggregate stability of Vertisols. Low infiltration, leading to runoff and loss of sparse precipitation, is a problem in many semiarid tropical areas. Where the soil contains swelling clay minerals, as in semiarid India where this work was conducted, water stable aggregates are essential for infiltration and hence availability of water for plants. The influence of arbuscular mycorrhiza (AM) on aggregate stability of vertisols was studied in a pot experiment in which sorghum was grown in sterilized soil inoculated with mycorrhizal inoculum as well as in sterilized and unsterilized control soils. Part of the soil in the pots was separated from the roots by a nylon mesh bag. Aggregate stability of the soil inside and outside the mesh bags was studied at harvest, after 10 weeks of plant growth. Water stability of aggregates was determined by wet sieving and turbidimetric measurements, and AM was quantified as colonized root length and hyphal length. Wet sieving of soil from outside the mesh bags showed greater "mean diameter weight" (MDW) in the soil inoculated with mycorrhiza than in non-inoculated soil. However, unsterilized soil showed equally high MDW despite the fact that the sterilization process itself had been proven to increase the MDW before the experiment. Inside the mesh bags there was no significant effect of the inoculation, but the unsterilized soil showed a higher MDW. The turbidimetric measurements of the bulk soil showed the highest aggregate stability in the sterilized and inoculated soil. Although the unsterilized soil had the lowest stability, it showed the largest increase in stability. These results show that mycorrhiza affects the aggregate stability and that both increased root growth and mycorrhizal hypha is involved.